Bites and Stings: An Overview of Close Encounters with Nature. Part I

Bites and Stings: An Overview of Close Encounters with Nature. Part I

Authors: Gary D. Hals MD, PhD, Attending Physician, Department of Emergency Medicine. Palmetto Richland Memorial Hospital, Columbia, SC; and Eric Brittain, MD, Resident Physician, Department of Emergency Medicine, Palmetto Richland Memorial Hospital, Columbia, SC.

Peer Reviewers: J. Stephan Stapczynski, MD, Chair, Emergency Medicine, Department, Maricopa Medical Center, Phoenix, AZ; and Steven M. Winograd, MD, FACEP, Attending Physician, Emergency Department, Adena Regional Medical Center, Chillicothe, OH.

Often unseen, nature surrounds people in their daily lives, not only outside but even in homes, offices, and hospitals. With exceptions of high mountain tops and deep oceans, there is nowhere people can go on earth to completely avoid contact with bugs and other critters. Consequently, there is a wide variety of animals, insects, and reptiles that can bite or sting humans. From dogs to black widow spiders to venomous snakes, the results of these encounters can vary from inconsequential to deadly. In most cases animals attack only in defense of their habitat or lives, but in some situations they actively seek out humans as a food source. The precise numbers of patients bitten and stung cannot be known, as most people do not seek treatment, but millions of people are victims every year.

Some encounters are mundane and go unnoticed, but often contact with the myriad of creatures with which people share the globe with cause them harm. The effects they produce vary widely from life-threatening to simply annoying. Some insects that normally would produce only a mildly irritating sting in most people can cause unexpected anaphylactic reactions in others. The exact path each envenomation will take unfortunately is not always clear from the initial assessment. With such variable and unpredictable results, bites and stings can be vexing for the ED physician to assess and treat. The purpose of this paper is to provide an overview for treatment of the most important bites and stings encountered in the United States. Due to the popularity of the exotic pet trade, some non-native species now commonly held in captivity in private homes in the United States also will be discussed, especially when specific anti-venom is available. — The Editor

Animal Bites

Domestic Animals. Bites from domestic animals are all too common, and in part injuries are due to large numbers of dogs and cats in the United States. In a 1998 survey of pet owners, 39 million households owned at least one dog, and 32 million owned at least one cat.¹ Current numbers probably exceed 50 million each. Of course, these estimates do not include stray animals. An estimated 4-5 million people (1.8% of the U.S. population) are bitten each year by dogs alone.¹ Thus, dogs account for 60-90 % of all bite injuries treated in the ED. Exact numbers are impossible to obtain as roughly only 1 in 775 people bitten seeks medical treatment.² Cats are responsible for up to another 5-10 % of animal bites or at least 500,000 patients. Altogether, it is estimated that cat and dog bites account for 1% of all ED visits, about 10,000 admissions and roughly 20 deaths annually.³ Fewer than 2% of other bite injuries are from less common or wild animals (i.e., ferrets, raccoons, foxes, livestock, bats, monkeys, minks, and other wild animals).⁴ One author estimates that 50% of all Americans will suffer a mammalian bite wound in their lifetime.⁵

Children are much more likely to be bitten by dogs than are adults, with 51% of bites occurring in patients younger than 12 years of age.⁶ The peak incidence for dog bites is in children ages 5-9 years.² When bitten, children are 3.2 times more likely to present to the ED for treatment than adults.⁷ Boys are injured more commonly than girls, and a member of the family usually owns the dog. Children typically are bitten while playing with the animal. In contrast, females are more likely to be bitten by cats, and the animals more often are strays. Dog bites tend to occur most frequently on the lower extremity in adults while cat bites are most common on the upper extremity. However, in children younger than 2 years, bites more frequently occur on the head and face, as a large dog’s mouth is at head level for a small child. Dog canine teeth can puncture the skull, placing small children at higher risk for depressed skull fractures, brain laceration, intracranial abscess, and meningitis.⁸

Certain breeds of dog, such as chow, pit bull, Rottweiler, German shepherd, and other large guard dogs, are responsible for the majority of serious bites. One survey of 356 dog bites found that German shepherd and chow breeds were responsible for the majority of injuries.⁶ Other than breed, the highest risks were with unneutered, male dogs housed with young children and chained in their own yard.⁶ Bites to the hand can be especially problematic and prone to infection (see next section on treatment). Amputations and deaths from dog bites, fortunately, are rare, and most deaths are due to exsanguination rather than severity of bites. Approximately 20 people die each year from dog bites, 55% of which are caused by pit bull or Rottweiler breeds.⁹ Most states have reporting laws for animal bites, and require reporting of animal bites to the appropriate agency prior to discharge.

Treatment of Dog Bites. Dog bites tend to cause more widespread damage than cat bites, and 4% of dog bite victims will be admitted.² Dog’s canine teeth are wider, and their strong jaws can exert considerable pressure (up to 200 psi) causing large areas of soft-tissue damage. Although injury from most dog bites is limited to skin and muscle, significant damage to deep structures (i.e., vessels, tendons, nerves, and bones) can occur. Deep structure injury can be occult, and sometimes small external wounds may be misleading as to the true nature of the injury. Especially with bites to the hand, complete clinical examination should be performed to exclude occult deep structure injury. X-rays may be required to evaluate for possible fracture and/or retained animal teeth fragments. After adequate local anesthesia, wounds should be explored in a sterile field to assess for tendon injury, joint penetration, or other injury that may require repair. Though rare, any bites to the neck should be evaluated for injury to the carotid artery or jugular vein. A bruit at the area of the bite wound can be a clue that an intimal flap may be present, and angiography may be needed to diagnose this injury.

Though dog bites can become infected, it is surprising that the overall incidence of infection is not much higher than non-bite wounds sutured in the ED: 5-10% for dog bites vs. 3-7% for all other sutured wounds.¹⁰ One study identified the extent and depth of the injury as well as patient age as risk factors that increased the rate of infection. Deep, full thickness wounds or those requiring surgical debridement increased risk of infection seven times, and patients older than 50 years of age were six times as likely to develop infection compared to younger patients.¹¹ The location of the bite also plays a role in the risk of subsequent infection. Dog bites to the hand have a notoriously higher rate of infection, from 12-30%, while bites to the face have a much lower rate of 0-5%.¹² Care is needed to examine closely for signs of infection when treating patients with delayed presentations. A delay of only 10-24 hours substantially can increase the risk of infection.¹³

Pasteurella multocida usually receives the lion’s share of attention when discussing microbiology of infected dog bites, but most infected wounds are polymicrobial infections with greater than 100 different organisms identified as causing infected dog bites.¹⁴ Infected wounds are truly polymicrobial with no single organism responsible for more than 30% of infections.¹⁵ Infected dog bite wounds usually have both aerobic and anaerobic organisms present; one prospective study found an average of five isolates per wound.¹⁶ Aerobic organisms typically do not produce beta-lactamase, and common examples include: Staphylococcus aureus, alpha-hemolytic and beta-hemolytic streptococci, Capnocytophaga canimorsus, Klebsiella, Bacillus subtilis, Pseudomonas, and Enterobacteriaceae. Anaerobic organisms typically found include: Bacteroides, Fusobacterium, Peptostreptococcus, and Actinomyces species. P. multocida species are a very common isolate from cat mouths (77%—see next section), but are only found in 13% of dog mouths.¹⁷ A variety of Pasteurella species are found in infected dog bites and usually are less potent than P. multocida, whereas P. multocida isolated from infected cat bites can be the sole pathogen.¹⁸

Cultures may not always reflect the full spectrum of pathogens present in the wound. Several authors have noted that local laboratories may not always recognize more unusual organisms, in part because these species are much harder to culture than normal bacteria. Further, infected bites may have atypical species that often are not associated with human infection present.¹⁶ An example is the gram-negative rod Capnocytophaga canimorsus, often part of the normal flora of dog mouths. C. canimorsus requires special media and growth conditions, but even then only grows slowly, taking up to 14 days to become evident.¹⁹ It has been responsible for infection and sepsis in more than 100 cases since discovered in 1976²⁰, and 90% of the cases have been related to dog bites.²¹ Cutaneous gangrene in the bite wound is highly suspicious for C. canimorsus infection, and immunocompromised patients (asplenia, chronic steroid use, alcoholics, end-stage renal disease, HIV/AIDS) are at much higher risk.²¹

Multiple studies have shown that prophylactic antibiotics are not recommended routinely for all dog bite wounds,¹⁴ and meta-analyses have confirmed this recommendation.²² However, it consistently has been shown that prophylactic antibiotics do help prevent infection in a subset of high-risk wounds.²³ Most authors recommend prophylaxis for deep dog bite wounds, for any bites to the hand,²³ or in immunocompromised patients.¹² The choice of antibiotic to use is less clear as no single drug can cover all possible pathogens known to infect dog bite wounds. General recommendations are summarized in Table 1. Amoxicillin/clavulanic acid (Augmentin) is the first choice (as for most bite wounds) if the patient is not penicillin-allergic, with azithromycin (Zithromax) as the alternative. Community-acquired multi-resistant Staphylococcus aureus (CA-MRSA) has, to date, not been isolated from infected dog bite wounds, so specific antimicrobial therapy directed against this pathogen does not need to be considered.

Finally, although a subject of much debate in the past, most authors now agree that facial dog bite wounds may be closed safely with sutures to reduce scarring.^10,14,24 (See Table 2.) This should be done only after cleaning the wound with diluted povidone iodine (Betadine), examination under local anesthesia to exclude deep structure injury, irrigation with saline, and debridement of any devitalized tissue. (See Table 2).

The location of the bite clearly affects the risk of infection, with hand wounds at significantly higher risk than facial wounds. As a result, many practitioners would probably feel comfortable suturing facial dog bite wounds and less comfortable closing similar wounds on the hand. Interestingly, a controlled study found no difference in rate of infection with sutured vs. unsutured dog bite wounds even though no prophylactic antibiotics were given.²⁵ The authors examined 169 wounds and found the same rate of infection when bite wounds were sutured or left to heal by secondary intention (7.7%). They did observe a higher rate of infection in hand wounds (12%) regardless of closure method. This would suggest that hand wounds may be closed without increasing risk of infection. A conservative approach might be to close larger hand wounds only loosely, and be sure that any exposed tendon or bone is covered. Using prophylactic antibiotics for bites to the hand would likely further reduce the risk of infection. Any significant injury (tissue defect, deep structure injury, cosmetic concern) should have surgical consultation to best determine care while the patient is in the ED. Rabies and tetanus prophylaxis recommendations are summarized in Table 3, Table 4, and Table 5.

Treatment of Cat Bites. Cat teeth typically produce puncture wounds as opposed to the larger skin damage dog’s teeth cause. The long, thin nature of cat’s teeth predispose patients to deep structure injury, as joint spaces, tendons, and even bones can be punctured. Thus cat bites cause higher incidence of osteomyelitis and septic arthritis than do dog bites.²⁶ Puncture wounds also inoculate bacteria deep into the wound, giving cat bites a much higher risk of cellulitis than dog bites (30-50% for cat bites vs 5-10% for dog bites).^10,27 It is difficult, if not impossible, to adequately irrigate and clean puncture wounds in the ED. The fact that 63% of cat bites occur on the hand,¹⁶ a high-risk location with dog bites, probably also increases the incidence. Cat bite infections also more often are present upon initial presentation, and up to 24% of patients will require hospitalization.²⁷

Pasteurella multocida and P. septica are common pathogens in infected cat bites, accounting for 75% of isolates in one series.¹⁶ Like dog bites, though, most are mixed polymicrobial infections with aerobic (e.g., alpha-hemolytic streptococci and S. aureus) and anaerobic (e.g., Bacteroides and Prevotella species) bacteria present. One series found a median of five isolates per infected cat bite wound, with a maximum of 16.¹⁶ P. multocida wound infections are aggressive with early onset of symptoms (fewer than 6 hours) and rapid progression. Infections usually are evident in fewer than 24 hours, whereas other non-Pasteurella bacteria may take 2-3 days to become visible.¹⁴ Further, P. multocida can produce abscesses and septic arthritis by seeding distant sites from the bite. Endocarditis and meningitis also have been documented.²⁸ As with any infection, patients with underlying disease (i.e., diabetes, liver disease, renal disease, cancer, HIV/AIDS) are at higher risk for serious complications.

Unlike dog bites, prophylactic antibiotics are recommended by many authors for cat bite wounds, especially to the hand.²⁹ Though most practitioners prescribe them, a meta-analysis of randomized controlled studies suggests that prophylactic antibiotics are not indicated for every cat bite, but do show that they reduce infection for bites to the hand.²² Prophylactic antibiotics also are recommended by standard texts in emergency medicine.¹⁴ Antibiotics should be used that specifically cover P. multocida, S. aureus, and Streptococcus species. Amoxicillin-clavulanate is a good first choice, with levofloxacin (Levaquin) or azithromycin for penicillin-allergic patients. (See Table 1.)

The majority of cat bite wounds will not require suturing as they are small puncture wounds. (See Table 2.) Although studies find that primary closure of bite wounds is safe, and infection rates vary from 0%²⁷ to 6%³⁰, most authors still recommend that these small puncture wounds be left open.¹⁴ The risk of infection generally is higher than the benefit from wound closure. This is especially true for bites to the hand, where primary closure of small wounds should be avoided. Large wounds are less common from cat bites; any cosmetically disfiguring wounds to the face should be referred for consultation or closed primarily in the ED.²⁴

Wild or Unknown Animal Bites. Just as the actual incidence of bite wounds from domestic animals is difficult to quantify, the incidence of wild animal bites is even harder to calculate. While a large number of humans are attacked by mammals and die worldwide (several thousand deaths from tigers and lions in Africa and Asia), those dying from other animal encounters is much greater. The estimated number of human deaths from reptile bites is around 60,000, and the number from insect-borne illnesses is in the millions.³¹ In terms of the United States, of the estimated 200 people killed in animal encounters each year, 131 of these are in automobile accidents involving deer on the roadways.³¹ Just as the exotic reptile trade is expanding every year, so is the exotic mammal trade, and it is now possible for previously unheard-of animal attacks (i.e., lion, tiger, etc.) to occur in nearly every state.

General treatment of a wild animal bite should proceed much like evaluation of any other trauma patient. Trauma is largely defined by mechanism of injury, therefore it is important to know what kind of animal attacked the patient. This data may not be directly available, but the size of the animal will be most useful in determining what types of injuries to look for. Any large animal easily can produce internal injuries besides obvious external damage, and the evaluation should proceed similarly to any evaluation of a blunt or penetrating trauma patient. Realize that a 100-lb animal may not be very large for an adult, but can severely injure a small child. Bites to the head should be evaluated for penetration of the skull. Bites wounds from large animals are a combination crush injury and penetrating injury, and devitalized tissue should be debrided carefully. This will serve to prevent infection more effectively than irrigation alone. Routine wound cultures are not useful, as they do not accurately predict future wound infection or the pathogens that produces it.³¹ Choice of primary wound closure will depend on cosmetic concerns, function, and infection risk. Facial bite wounds can be closed safely when presenting early (fewer than 24 hours) without signs of infection, although large wounds should be referred to the consultant. Bites to the hand and foot have the highest risk of altered function, and also are high risk for infection; these wounds generally should be left open for delayed or secondary closure. Bite wounds of certain species seem more prone to infection than others, but have not been well-studied. Bite wounds from large cats, primates, pigs or alligators/crocodiles are considered high risk for infection. These wounds should be left open and treated with prophylactic antibiotics. (See below and Table 1.)

Rabies. Rabies is one of the oldest described diseases and has been described as early as the 23rd century BC.³² Rabies is caused by an RNA virus and typically is transmitted through the bite of an infected animal. Non-bite related (i.e., scratches, licking of skin) transmission of rabies is rare. Since rabies transmission in animals often occurs from eating infected prey, only the bites of carnivores normally are considered at risk for rabies. Thus bites from rabbits or small rodents (i.e., mice, rats, hamsters, squirrels, guinea pigs, gerbils, chipmunks) almost never require rabies prophylaxis. The major wild animal reservoirs in the United States are in bats, raccoons, skunks, and foxes but any carnivore potentially can transmit the disease (i.e, dogs, cats, coyotes, wolves). Fortunately, cases of rabies are rare in the United States, with roughly five or fewer cases each year since 1960³³ and one-third of these cases originated from animal bites received in foreign countries. Of the 37 cases diagnosed in the United States since 1980, 88% have been caused by bats.³⁴

The rate of symptom onset depends on the location of the bite as the virus spreads to the central nervous system (CNS) via the peripheral nerves. Thus bites to the face may produce symptoms in as few as 14 days, but bites to the foot may take 60 days or longer. Often there are no immediate signs of infection. Fewer than half of patients will note itching or paresthesias at the wound site.³⁵ Most clinical symptoms develop between 2 and 16 weeks.³⁵ Symptoms begin with non-specific viral complaints of fever, headache, nausea, vomiting, sore throat, abdominal pain, fatigue, anxiety, and ultimately progress to encephalitis and death. Since after it develops rabies is (almost) 100% fatal, prevention is essential. Only five previously vaccinated people were known to survive rabies infection, and until recently unvaccinated patients have never survived once symptoms began. In December 2004, the first known exception to this occurred when an unvaccinated teenage girl in Wisconsin survived rabies contracted from a bat. Doctors apparently used novel treatment (medical coma) that will require further study to verify efficacy.³⁶

General recommendations for prophylaxis are to consider the species of the biting animal and the conditions under which the bite occurred. (See Table 3.)

Small rodents (i.e., mice, rats, etc.) are very low risk for rabies transmission, while small carnivores (i.e., raccoons, skunks, foxes, and bats) are higher risk. The preponderance of human rabies in the United States is associated with bats, and special consideration is given to this animal. (See Section on Bats.) All witnessed bat bites require rabies prophylaxis, and prophylaxis also is recommended even cases of questioned contact (i.e., a bat found in room with non-verbal or sleeping individual). One should attempt to determine if the biting animal displayed any symptoms consistent with rabies infection. Examples are previously friendly dogs or cats that salivate excessively and become unusually aggressive. Wild animals that approach humans without fear and are active during the day if nocturnal also are clues for possible rabies infection. Being bitten while separating fighting animals, feeding a wild animal, or provoking the animal (i.e., approaching a mother with babies) is an expected result of such encounters, and should not be considered a high risk bite. Infected animals will display signs of rabies that become more evident as the disease progresses. Signs to note are: staggering gait, being sensitive and hyperresponsive to external stimuli (sound, touch), restlessness, uncomfortable, unusually frequent vocalization, and seizures. Unusual itching or paresthesias at the bite wound site are the only early sign of rabies infection, and occur in fewer than 50% of cases, but patients should be asked about these symptoms. When present, one should strongly consider prophylaxis.

Rabies prophylaxis is outlined in Table 4. Several specific points about prophylaxis should be understood. Cleaning the wound well with soap and water, followed by povidone-iodine (if available) as soon as possible is an easy and very effective way to reduce the risk of rabies transmission. Prophylaxis doses listed are the same for children or adults. Pregnant or nursing mothers also are treated the same as other adults. The incidence of side effects to human rabies immune globulin (HRIG) is low (1-5%) and consist mostly of local reaction at the injection site. Serum sickness was associated with early forms of HRIG but is not found with current forms. Anaphylaxis or transmission of HIV/hepatitis has not been reported with HRIG use.³⁵ Side effects with human diploid cell vaccine (HDCV) and purified chick embryo cell vaccine (PCEC) are more common (5-40% of patients) and vary from more common local reactions to rare systemic allergic reaction. Beware not to use the same syringe or injection site for HRIG and HDCV or PCEC as the antibodies in HRIG may reduce effectiveness of the vaccination. HDCV and PCEC should be given in the deltoid in adults and in the thigh in children, and should not be given as a gluteal injection secondary to reduced efficacy.³⁷

Any immunocompromised patient should have their antibody titers checked 2-4 weeks after the vaccination series is completed. Specifically, HIV infection in the bitten patient has not been shown to reduce the effectiveness of prophylaxis. The target range for viral neutralizing antibody is at least 0.5 IU/mL 2-4 weeks after immunization series.³⁵ Additional booster doses are given weekly until antibody levels are acceptable. As abnormally long incubation periods of six years have been documented,³⁸ one should not use passage of time as a reason to withhold postexposure prophylaxis for a true exposure to rabies.

Tetanus. Tetanus is caused by infection of a wound with Clostridium tetani. These bacteria grow in an anaerobic environment. They produce a very potent toxin that interferes with neuromuscular transmission resulting in unopposed muscle spasm (e.g., lockjaw) as well as autonomic dysfunction. All bites are considered tetanus prone wounds, although there are only 25-100 cases of tetanus each year in the United States. Nearly all cases occur in those who never have been vaccinated, did not complete the primary series of three doses, or have not had a booster in more than 10 years. While some people obtain life-long immunity from their childhood immunization series, most individuals’ antibody levels fall after about 10 years. Puncture wounds are associated with more cases of tetanus than lacerations (50% vs 33% for cases reported between 1998 and 2000).³⁹ Although animal bites are a risk for tetanus, puncture wounds from stepping on a nail are still much higher risk for tetanus than are animal bites. Unlike rabies, clinical tetanus is treatable and 90% of patients will survive³⁹ although complete recovery may take several months. See Table 5 for recommendations of tetanus prophylaxis.

Rats, Mice, and Small Rodents. Bites from small rodents as a rule do not normally require medical attention, primarily due to their relatively small size. However, small children can receive significant injuries from larger rats, and rodent bites account for between 2% and 10% of all ED visits for bite wounds.⁴⁰ Rat bites become infected only 2-5% of the time, which is similar to the overall infection rate for traumatic wounds treated in the ED.⁴⁰ Any serious injury from a rodent bite is confined to small infants or disabled adults bitten on the face while sleeping, and reports exist of penetrating globe injuries.⁴¹ Rabies transmission is rare with wild rodents, and patients likely only need prophylaxis if the animal tests positive or if a known local outbreak of rabies in rodents occurs. Wild plague still is a problem though, with 362 cases documented in the western United States in the past 50 years.³¹ Rats carry the bacteria Yersinia pestis, and transmission occurs when fleas become infected biting the rat and then bite humans.

Bats. Bats basically can be thought of as mice with wings, and also cause very little damage from their small teeth. Most bat bites do not even penetrate skin and easily are overlooked. However, all bat bites should be considered high risk for rabies. Bats remain the most common cause of all rabies transmission in the United States and even contact with a bat where a bite cannot be excluded (i.e., small child in room with bat, non-verbal adult) should prompt postexposure prophylaxis. Observation of the bat is not recommended as they have been documented to shed virus for up to two weeks before becoming ill.³⁵

Primates. Monkeys and other primate bites are even higher risk than human bites for infection. Unfortunately. most bites become infected even when prophylactic antibiotics are given.⁴² No monkeys or primates are native to the United States, but animal trade has led to the presence of smaller primates in private homes. Larger primates such as chimpanzees and especially baboons (up to 90 lbs.) can inflict severe bites sometimes causing serious injury. Finger amputation or even death can occur as evidenced by the recent severe mauling of a couple in Bakersfield, CA in February 2005. Infections from primate bite wounds have similar characteristics to human bite wounds; multiple pathogens with mixed aerobic and anaerobic infections, and are treated as human bites. (See Table 1.)

Coyotes and Wolves. Coyote populations are continuing to rise in the United States, and documented attacks have occurred even in larger cities (e.g., Los Angeles).⁴³ Bites are similar to and treated as dog bites except that rabies prophylaxis is recommended unless the animal can be tested immediately after the attack. Wolves were reintroduced in Yellowstone and Idaho in 1995, but no attacks have been documented. If populations rise, though, a pattern similar to Europe where wolf attacks occur yearly may begin.

Skunks, Foxes, and Raccoons. Skunks often are found to be rabid when captured, but do not often bite as they tend to rely on spraying for defense. The liquid sprayed can cause significant eye irritation, but has not been documented to transmit rabies. Foxes do not usually bite humans due to the fact they are nocturnal and normally avoid human contact. Consequently, most fox bites are from rabid animals and should be considered high risk for rabies. Raccoons account for more than 50% of rabies documented in wild animal populations,⁴⁴ and bites are high risk for rabies for the same reasons as fox bites are. Data on other wound infections are not available, but prophylactic antibiotics should be considered for these bite wounds.

Swine. Wild populations of pigs are not very widespread in the United States, but pigs are a common source of bite wounds for certain high-risk occupations (i.e., veterinarians, farmers). Boars (male pigs) also have tusks that can cause large lacerations and penetrating injuries. Pig bites or goring injuries are high risk for infection. Bite wound infections yield multiple pathogens, including aerobic and anaerobic bacteria. Pigs also carry Pasteurella multocida. Any patient with a moderate or severe injury from pig bite or goring should be treated aggressively and considered for admission. Close follow-up is indicated if the patient is discharged.

Bears. Bears found in the United States include the black, brown, grizzly, and polar bears. Contrary to popular fears, bear attacks in the United States are rare, and the chances of being killed by lightning are five times higher than for a bear attack. When attacking, though, bears are capable of both severe blunt and penetrating trauma. Their paws are large and can contuse internal organs, and their teeth and claws can cause deep lacerations and puncture wounds. Their bite wounds are not significantly infectious and can be treated in a similar fashion to dog bites. General recommendations to avoid bear attack include remaining submissive in the presence of a mother with cubs, but to be threatening and aggressive to predatory bear behavior.⁴⁵ Apparently, playing dead is an effective response to a bear attack and seems to minimize injury.⁴⁴ The best advice is to avoid bear encounters by staying away from known bear habitats.

Big Cats. The cougar or mountain lion is the only big cat native to the United States that still is present here. Attacks by this animal are rare, with only 31 attacks (and five deaths) documented between 1970 and 1990.⁴⁵ Unfortunately, as the very public attack on Roy Horn of Seigfried and Roy shows, there are a number of non-native big cats in the United States, including lions, tigers, and leopards. Many of these are in the United States as a result of the exotic animal trade and attacks on people occur rarely but with regular frequency. Their large teeth can inflict deep puncture wounds, and they often attack at the neck or head to rapidly paralyze their prey. Besides crushing the larynx to asphyxiate (the favored technique of lions), they also shake their victims by the neck and quickly can sever the spinal cord. They also have the strength to kill instantly with one blow from their paws. Any victim of an attack by a big cat should be evaluated for penetrating as well as potential blunt trauma. Any penetrating wound to the neck should be evaluated fully for deep structure injury, even if small in appearance.³¹ Claws also can produce deep lacerations resulting in large vessel injury and/or nerve injury.

Large Herbivores. While horses and donkeys are found in large numbers on farms, and bites are not rare, but their teeth typically produce only soft-tissue contusions. Wound infections occur, but can be treated similar to dog or cat bites. Many other large herbivores are present across the United States, including deer, cows, bison, elk, and moose. Bison naturally are more aggressive than deer, moose, or elk, but male deer/elk/moose can be very aggressive during mating season. Domesticated cows usually are very calm, but bulls can produce serious injuries. All of these animals can gore a person with their horns, producing dangerous penetrating injuries. The larger the animal, the higher the risk of associated blunt trauma from being butted by their heads. Goring injuries seem to do well with debridement and prophylactic antibiotics.⁴⁴ In actuality, deer and moose cause large numbers of human injuries and deaths from collisions with cars. According to the National Highway Traffic Safety Administration, deer alone kill more than 200 people a year and injure thousands more. Older data from 1994 showed 56,000 collisions with deer in Michigan alone, with 1500 injuries and five deaths. Moose collisions are less common, but their larger size (more than 1000 lbs.) makes each accident more dangerous.

Exotic Animals. A few non-native species recently have begun to be raised on farms in the United States, notably ostrich and emu. Likewise, other non-native species, such as ferrets, have become popular as pets. Ostrich and emu are large birds that defend themselves by kicking and severely can injure people. They can kick only in a forward direction, but their sharp toes actually can disembowel or produce severe head injuries. As birds have no teeth, bites usually are more of a peck and do not cause significant injuries in adults.

Ferrets are very fast and have small sharp teeth, but most bites to adults are not serious. One study found that ferrets inflicted some severe injuries on unattended sleeping children and infants, where ferrets tended to bite the face and neck.⁴⁶ Ferret bites are not considered high risk for rabies or other infection and can be managed similarly to dog bites.

Human Bites

Exact statistics on the number of human bite victims are not readily available. Human bite wounds come in a variety of forms, and can be thought of as minor or major injuries in terms of their risk of complications.

Minor Human Bites. Minor human bite wounds occur commonly in young children, with one study of day care centers finding that 46% of children were bitten at least once during a one-year period.⁴⁷ These wounds often are just abrasions that have a relatively low risk of infection, similar to the average 6% level for any laceration treated in the ED. Prophylactic antibiotics may be given for these wounds, but often close follow-up for wound re-check is sufficient.

Human bite wounds occurring in the sense of an animal bite are called occlusional bites, and most often result from fights. One always should keep the possibility of child abuse or domestic abuse in mind when evaluating these injuries. These human bites are much more common in urban areas, accounting for anywhere from 3% to 23% of all bite wounds treated in the ED.⁴⁸ They typically are less serious than fight bites, but treatment can be controversial. (See Section on Treatment of Human Bites.) Prophylactic antibiotics should be considered in any patient with any laceration or puncture wound resulting from a human bite. (See Table 1.)

Fight Bites. The most serious is the bite wound equivalent, also called the fight bite or clenched fist injury. These injuries are not rare, and unfortunately complications are common and serious. Up to 62% of fight bite wounds will have penetration of the joint, and 58% will have bony injury.⁴⁹ Laceration of the extensor tendon is a surrogate marker for joint penetration. These wounds are at very high risk for infection, and one series found a 50% infection rate of seemingly innocuous fight bites in patients who presented in fewer than 24 hours and had no early signs of infection or deep structure injury.⁵⁰ Patients presenting late (within more than 24 hours) usually are brought to the ED by symptoms of an established infection and are at the highest risk for complications, including joint stiffness, arthritis, osteomyelitis, amputation, sepsis, and even death.⁵⁰ Joint space infections are common, progress rapidly, and are quite destructive. Once destroyed, few surgical options exist for repair or replacement of the metacarpal-phalangeal (MCP) joint. Permanent hand disability results, often in young patients in the prime of their working lives. To make matters worse, patients with fight bite injuries notoriously are non-compliant and often under the influence of alcohol or drugs, making accurate histories problematic. Consequently, many patients with fight bites present late in the course (more than 24 hours). Those presenting late with established infections should be referred to a hand surgeon for admission, intravenous antibiotics, and surgical debridement. Those presenting in fewer than 24 hours from injury without signs of infection should have X-rays and their wounds explored under sterile conditions to exclude deep structure injury. Those with tendon injury, joint penetration, retained foreign body, or fracture should be referred to the consultant. Prophylactic antibiotics are indicated for any fight bite, and standard choices are amoxicillin/clavulanate or clindamycin plus ciprofloxacin for penicillin-allergic patients. (See Table 1.)

Treatment of Human Bites. Risk of infection from human bite wounds generally is more common than in animal bites, with high rates of infection (38%) quoted in the literature.⁵¹ However, at least one recent paper suggested not all human bites are more prone to infection than other animal bites.⁵² Their study of low-risk human bites (abrasions or lack of epidermal injury) found no decrease in infection when prophylactic antibiotics were given, however the rate of infection with placebo also was low (less than 1%).⁵² The authors excluded any human bites resulting in lacerations and/or puncture wounds, as these still are considered high risk for infection.⁵³ Further, these authors also admit that infection from human bites to the hand (fight bites) are very common. One prospective randomized trial that tried to debunk the idea that hand infections are not as common as perceived found that 47% of hand bite wounds became infected without prophylactic antibiotics, compared to fewer than 1% rates for prophylactic treatment.⁵⁰

Human saliva has at least 42 different species of bacteria. As with animal bites, infections from human bites are polymicrobial in nature, with an average of five pathogens isolated from each wound.⁵⁴ Most of the data comes from analysis of fight bites where S. aureus and Streptococci are the most common aerobic organisms, but anaerobes are found in up to 50% of the same wounds.⁴² Oral flora also are common isolates, with anaerobes such as Eikenella corrodens, which normally is found in dental plaque. Antibiotic recommendations are given in Table 1.

Another consideration in human bites is the transmission of contagious diseases. Unfortunately, many disease have been documented to be transmitted via human bites, such as HIV, herpes, syphilis, tuberculosis, herpes, hepatitis C, and hepatitis B.⁵⁵ Fortunately, the cases of HIV transmission are rare and have involved a significant mixing of blood along with saliva.¹⁴ Although HIV virus is present in the saliva of 44% of patients with HIV, the amounts are very low, and the CDC does not consider human bites to carry a risk of HIV transmission unless significant exposure to blood occurs at the same time. One should discuss the case with local infectious disease consultants (or the CDC’s postexposure prophylaxis hotline: 1-888-448-4911) for any question of treatment with post-exposure prophylaxis.

Primary closure of occlusional human bite wounds in the majority of cases is not a concern as most bites to the trunk or limbs are crush injuries, or produce only superficial abrasions. (See Table 2.) All puncture wounds should be left open. Bites to the hand or fight bites should be left open as well (although a recent case report exists of a primary tendon repair that was closed successfully.⁵⁶ As mentioned previously, any fight bite should be examined under sterile conditions to exclude deep structure injury. Any extensor tendon injury highly correlates with joint penetration. The detection of any deep structure injury should prompt consultation with the hand consultant for possible admission. Likewise, any patient with an infected fight bite should be admitted for further treatment.

Occasionally bites to smaller areas such as the nose, ears, or fingers can result in lacerations, avulsions, or amputations. True tissue defects or amputations require specialty consultation for definitive management, but the question of whether to close lacerations from human bite wounds can be controversial. In general, most recent emergency medicine texts agree that primary closure of deforming facial bite wounds can be performed safely.^57,58 This is supported by a recent study of facial bites that found primary closure after debridement (if necessary) followed by a one-week course of antibiotics yielded complete healing at time of suture removal in 90% of cases.⁵⁹ These results are impressive considering the age of the wounds ranged from 1-4 days. If any signs of infection already are present, or the physician is not comfortable with primary closure, careful debridement followed by delayed closure (2-3 days) is a good alternative.⁶⁰

Insects

Insects are the largest group of the Arthropod phylum, which includes animals with segmented bodies and jointed appendages, and comprises 80% of all known animals in the world. Though actual numbers are not possible to obtain, insect envenomations occur in the millions every year. Venomous insects also account for more deaths annually than do snake envenomations. In contrast to venomous reptiles where the toxicity of the venom is responsible for deaths, the majority of deaths from insect encounters come as a result of anaphylactic reactions to the venom. As humans are not prey for any carnivorous insect, envenomation by the insect is strictly defensive, accidental, or reflexive. Though a large number of insects can sting or bite people, this discussion will focus only on those that are medically significant. As with all bites and stings, tetanus prophylaxis is recommended if not already current, but bites and stings from insects are not particularly associated with tetanus infection.

Spiders. Fear of spiders (arachnophobia) is a very common fear and dates back to the Middle Ages when spiders were thought to be carriers of the plague, and many diseases were thought to be a result of spider bites. The truth is that spiders are small carnivores that likely prevent disease by preying on insects that do carry disease (i.e., ticks, flies, etc.). There are roughly 34,000 species of spiders found in the world and they have managed to colonize all habitats except the open ocean. All spiders have eight legs attached to the thorax and the unique ability to produce silk from the spinneretes on their abdomens. Venom is produced by glands near the jaws located under the eyes. Like venomous snakes, the toxins in the venom vary widely among species and even in geographically isolated populations of the same species. The primary purpose of venom is prey capture, and spiders only bite in self-defense when provoked or threatened. The vast majority of spiders are incapable of causing humans harm because their venom is ineffective against mammals, they cannot inject sufficient quantity of venom, or their fangs are unable to penetrate human skin.

Making the diagnosis of spider bite is complicated by the fact that spiders seldom are seen following a bite. Few patients (12%) bring the spider in for identification, and only 20% report even seeing a spider when presenting to the ED with the complaint of spider bite.⁶¹ Spider bites do not have pathognomic clinical signs; therefore, other diagnoses should be considered strongly when evaluating a possible spider bite. Differential diagnoses that must be considered in the treatment of a suspected local reaction to a spider bite include fungal, bacterial, and viral infections; vesiculobullous diseases; other bites and stings; foreign body reactions; and systemic conditions that lead to focal skin lesions.⁶¹ When treating a patient with a suspected systemic reaction to a spider bite one should consider snakebite, scorpion bites, pesticide toxicity, sepsis, meningitis, encephalitis, or disorders that produce an acute abdomen (in the case of a black widow spider bite).⁶¹ Anatomic location of a bite is helpful as spiders tend to bite in areas where clothing binds. Spider bites occur more commonly in thin skin versus calloused skin secondary to the spider’s decreased ability to penetrate the skin.⁶² Of the relatively few spiders found in the United States that are considered medically important, only the black widow spider and the brown recluse spider are dangerous to humans. Tarantulas can cause harm, but are not life- or limb-threatening.

Black Widow (Latrodectus mactans). With its red hourglass marking, the black widow spider is one of the most widely recognized insects in the United States, and is found throughout the world. In the United States, it is found in every state except Alaska. There actually are several species of black widow in this country, but envenomations are treated similarly. The name is a bit misleading as not all widow spiders are black; some species are brown as adults, immature females are brown before they turn black, and yet others have red legs. Black widow spiders easily are identified. They are large, with a body approximately 2 cm in length, and a leg span approximately 4-5 cm. They are shiny black in color with the distinctive red/orange hourglass on the ventral abdomen. In some cases, the center of the hourglass may be absent, giving the appearance of two red dots instead. The hourglass on immature spiders also will not be as well developed as the adults. Only the female is harmful as the male is too small to bite humans effectively. These spiders are shy and nocturnal by nature, but females are known to be aggressive when guarding webs containing an egg case. Webs are small and disorganized in appearance (cob webs) compared to the highly organized orb spider webs designed to catch flying insects. They tend to be found under rocks, in wood piles, in barns, stables, and outhouses.

Bites tend to occur between April and October and are not rare. More than 2700 were reported to the American Association of Poison Control Centers (AAPCC) in 2002, with more than one-third treated in hospitals.⁶³ Although an average of four deaths per year occurred in the past, no deaths have been reported since 1983. Bites are defensive except in the case of a female guarding her egg case. Bites most often occur on extremities (lower more often than upper), but used to occur frequently on and around the genitals when spiders commonly were encountered in outhouses. The bite itself typically produces little immediate pain. Most people describe a pricking sensation similar to a needle or thorn which quickly fades. Black widow spider venom varies little between species and is the most potent neurotoxic venom of any spider.⁶⁴ The active component is alpha-latrotoxin, which opens cation channels on presynaptic nerve membranes causing transmitter release. When systemic symptoms occur, the neurotransmitter release produces muscle cramping and involuntary spasm, which can be severe. However these muscle spasms do not appear to increase serum creatine kinase. This cramping and pain develops in as few as 30 minutes or as long as two hours. Pain may involve the entire extremity or may center in the back, chest, or abdomen depending on the location of the bite. This pain can be severe and colicky, mimicking an acute abdomen.⁶⁵ Latrodectus facies refers to a spasm of facial muscles, edematous eyelids, and lacrimation that can be seen in some patients, and has been mistaken as an allergic reaction. With the onset of pain, a target or halo lesion may appear at the bite site; a flat erythematous ring extending 5-15 mm away from a central pale area. This target lesion is not dramatic, only lasts up to 12 hours, and may be overlooked. Other systemic effects include regional lymph node tenderness, and autonomic symptoms (nausea, vomiting, sweating, fever, salvation, hypertension, tachycardia, and, rarely, priapism). Not every patient will develop systemic effects,⁶⁶ but 60% of patients develop hypertension after a bite.⁶⁷ Envenomations are graded as mild for local signs only, moderate for muscle cramping of the extremities, and severe when vital signs (blood pressure) are abnormal or cramps involve the trunk. Deaths, fortunately, are rare and arise from respiratory muscle weakness. In most cases, the patient’s symptoms spontaneously resolve in several days, although pain has been reported to last for 1-3 weeks. When it does persist, the worst pain still only lasts 8-12 hours after the bite and usually is cyclic in nature.

Treatment of black widow spider envenomations varies from symptomatic treatment to admission for control of hypertension and pain, to use of antivenom for some patients. Most patients are managed without antivenom, and pain is controlled with IV opiates and/or benzodiazepines. Calcium gluconate infusion was recommended in the past, but is not effective and is no longer suggested as treatment.⁶⁷ Significant hypertension may require nitroprusside or nifedipine to control. Antivenom (Antivenin Latrodectus mactans) is available in the United States, but is recommended only for cases with severe systemic symptoms, such as significant hypertension, seizures, or respiratory arrest. Some authors recommend antivenom in pregnant patients, as premature labor has been reported. The decision to use antivenom should not be taken lightly, as a death from anaphylaxis in the United States has been documented.⁶⁷ However, it should be pointed out that in that case antivenom was not diluted and was given as a rapid IV push in a patient with known multiple allergies. Slow administration (over 20-30 minutes) of diluted antivenom is considered safe by most authors.⁶⁸ Antivenom does provide an advantage in that it is so effective even patients with severe reactions can be discharged from the ED after symptoms clearly have resolved. Typical antivenom dose is 1-3 vials. Most authors recommend admission for patients with intractable pain, a history of hypertension or heart disease, pregnant women, or children with moderate to severe symptoms.

Brown Recluse (Loxosceles recluse). The brown recluse (or fiddle back) is the other well-known spider found in the United States that is dangerous to humans. While there are 13 species of recluse in this country, only five have been documented to cause the notorious necrotic lesions (loxoscelism). Brown recluse spiders are found primarily in south-central United States, but sometimes can be found outside this range. They are named accurately, as they tend to live in warm, dry areas away from disturbances. When they live in houses, they more often are found in out of the way places like attics, basements, unused closets, under porches, etc. Outside they tend to be found under wood piles or rocks. They are identified less easily compared to the black widow spider. A brown recluse is a small brown spider with a body length about 1 cm and a leg span of fewer than 2 cm. It has a characteristic violin-shaped dark area on the dorsal thorax (as opposed to a red hourglass on the ventral abdomen in black widow spiders). While most people will not make a close enough examination to appreciate this fact, brown recluse spiders also have only three pairs of eyes compared to the usual four pairs seen in other spiders.

Although the brown recluse venom is not significantly different from other spiders, it does contain several enzymes, with sphingomyelinase D thought to be a primary cause of the necrotic lesions associated with their bites. The initial bite may or may not be noticed at first as many patients report no pain, and others only report a pinprick. The lack of pain during the bite often makes definitive identification of the spider impossible. Pain eventually develops in 3-4 hours along with a white area of vasoconstriction surrounding the bite. Induration usually also is present, and itching can occur. The lesions progress rather quickly to a central bleb surrounded by erythema, and eventually the bleb necroses and turns black. The necrotic center can retract below the skin surface, and usually is oblong in appearance. Necrotic areas have been reported to vary from 1-30 cm in size.⁶⁹ As tissue damage results from ischemia, the pain can be intense during the first 24 hours. During the next few days, the necrotic area gradually enlarges and forms an eschar, although the lesion may continue to grow in size over several weeks in some unlucky cases. When the eschar falls off, a large ulceration is left behind that can take weeks to months to heal. Bites over fatty tissue (i.e., buttocks, thighs, or abdomen) tend to have larger lesions as the venom produces pronounced ischemia there due to the relative lack of blood supply found in fatty tissue. Fortunately, muscle is spared but scarring can be extensive. Accurate identification of a brown recluse bite can be problematic if the spider is not identified, as more common conditions such as pyroderma gangrenosum, foreign body reactions, and Staphylococcal skin infections can produce similar lesions. Given the difficulty in accurate diagnosis, it is highly likely that the label of recluse spider bite is incorrectly applied to a large number of wounds.

Though large necrotic lesions tend to gather most of the attention, brown recluse bites can give systemic symptoms as well. Surprisingly, the systemic symptoms may be delayed and only appear in the first 24-72 hours. These symptoms include generalized complaints of chills, fever, vomiting, malaise, as well as hemolysis, thrombocytopenia, shock, jaundice, renal failure, hemorrhage, and pulmonary edema. Fortunately, systemic reactions are rare, but when they occur more often are seen in children. Deaths have been documented, but they are very unusual. While there is antivenom produced in Brazil, there is no antivenom available in the United States, and treatment of systemic symptoms is supportive. Obviously patients with systemic symptoms require admission for observation and supportive care. No laboratory tests are diagnostic of brown recluse bite, and recommended tests are aimed at identifying complications such as renal failure or hemolysis.

Treatment of brown recluse bites is based on the severity of the reaction, though no single method is accepted widely as providing proven benefit. Mild bites are treated with rest, ice, and elevation. Though somewhat counterintuitive as skin damage is produced by ischemia, heat application to the bites is reported to increase severity of the lesions.⁷⁰ As expected, hyperbaric oxygen recently has been shown to decrease lesion size in animal studies.⁷¹ Patients with suspicious or identified bites should be observed in the ED for 4-6 hours and, if no necrosis or pain is present by that time, they can be discharged safely. Small children may benefit from admission for observation as systemic symptoms are seen more often in children. For patients with active necrosis, dapsone 50-100 mg BID is recommended, though not proven effective by controlled studies. Further, dapsone use is associated with hypersensitivity reactions, methemoglobinemia, and hemolysis in the presence of G6PD deficiency.⁶⁹ Though wounds may look infected in appearance early on, antibiotics are not useful if wounds are not infected secondarily. As is the case with frostbite, early surgery is not advised by most authors, and delayed excision is the preferred approach. Steroids (e.g., prednisone) have not been shown to be helpful for local necrosis, but may be useful in treating systemic symptoms. Patients must be followed with frequent rechecks as open wounds are prone to infection in some cases. Any patient with active necrosis should have consultation with a plastic surgeon or dermatologist while in the ED, and admission may be useful although this must be decided on a case-by-case basis.

Hobo Spider (Tegenaria agrestis). Envenomation by hobo spiders also produce a clinical picture similar to that of the brown recluse spider, but they are not found in the same geographic areas of the United States. The hobo spider is a species originating in Europe, that was introduced to the Seattle area, and now is found throughout the Pacific Northwest from central Utah to southern Alaska.⁷² Hobo spiders are brown with gray markings, and are relatively large with a 7- to 14-mm body length and 27- to 45-mm leg span. They live in moist dark areas such as woodpiles or basements, but unlike the brown recluse tend to be aggressive and bite with minimal provocation. The hobo spider builds funnel webs in which they ambush prey and drag them into the funnel. Funnel webs are long-lasting because the spider continues to add on daily. Hobo spiders prefer disturbed darkened habitats close to the ground, i.e., wood lots, train tracks, and basements.⁶¹ Male bites have more pronounced effects on mammals than female bites, and for unknown reasons bites tend to be more severe during the winter months.⁶¹ The venom of the hobo spider is not well characterized, and no necrotoxic agent has been identified. Like brown recluse bites, hobo spider bites usually are painless, with the site becoming indurated followed by expanding erythema and blister formation. The blisters rupture, forming encrusted cratered wounds that heal gradually leaving a large, permanent scar. Healing typical occurs within 45 days.⁶⁴ Again as with bites from the recluse, rare patients may develop systemic reactions with severe headache, nausea, vomiting, diarrhea, lethargy, and aplastic anemia. Treatment again is supportive, and no single therapy is of proven benefit. Corticosteroids may aide in preventing aplastic anemia.⁶⁴ Resultant wounds may require excision and grafting after borders are well established.

Tarantulas. Several species of tarantula are found in the southern United States and easily are identified by their larger size and hairy body. Envenomation by a tarantula is not dangerous and only requires symptomatic treatment. The only systemic symptom reported from tarantula bite is fever. Tarantula bites produce pain, swelling, and redness, but necrosis is not usually a feature of their bites. A tarantula provides a warning before it bites because it must first raise up, lifting its front legs and resting back on its abdomen. If it does not, its fangs cannot be exposed effectively to bite. Besides envenomation, tarantulas possess urticating hairs on their abdomens that they effectively use for defense. These small hairs are located on their abdomens, and are released by flicking their hind legs on the underside of their abdomens in the direction of their attacker. The hairs are propelled airborne in the thousands and travel several meters. The hairs have small barbs and actually can penetrate human skin up to 2 mm, producing edematous, pruritic papules that can last for weeks. They are especially irritating if they enter the cornea.⁷³ Hairs on the skin can be removed with sticky tape and generous irrigation. Topical steroids also are useful to treat the reaction produced, and ocular steroids have been reported used for hairs in the cornea.⁷³

Scorpions. Scorpions are in the class Arachnid and are related to spiders and ticks. They are crab-shaped with two front claws and four sets of legs. The tail ends in a segment called the telson that contains a venom gland and a stinger. Scorpions contain very little in the way of jaws and only suck up the juices of their prey similar to spiders. Thus the bite of a scorpion is no consequence, but the stinger that delivers venom. Scorpions are nocturnal and hunt by grasping prey in the front claws and arching the stinger over to stab the prey. They can sting several times in rapid succession, but most of their venom is used in the first sting. An interesting side note is that scorpions will fluoresce when exposed to a black light (Wood’s lamp).

While there are more than 1300 scorpion species found throughout the world, the majority of them are innocuous. Their sting only produces mild local symptoms that can be treated with antihistamines (i.e., diphenhydramine) and NSAIDs (i.e., ibuprofen). There are approximately 30 species of scorpion found in the United States. There are several species found around the world that can produce systemic symptoms and can be considered deadly, but the only dangerous species native to this country is the Centruroides species (or bark scorpion). The other species of deadly scorpions are found in Africa, Central and South America, the Caribbean, the Middle East, and Asia. While perhaps not as popular in the pet trade as exotic venomous snakes, these species sometimes can be found in the United States kept as pets or, in rare cases, as stowaways in luggage. Together, it is estimated that scorpions kill about 5000 people worldwide, second only to venomous snakes.⁷⁴

Native U.S. Scorpions. Centruroides exilicauda is not widespread in the United States and is native only to Arizona, Texas, Southern California, and Mexico. Though only found in a few states, these scorpions constitute a relatively significant health problem. Nearly 10% of calls to the Banner Poison Control Center in Phoenix are for scorpion stings.⁷⁴ It may surprise the reader to note there were 15,687 scorpion envenomations reported to the AAPCC in 2002, compared to a total of 2325 bites reported from venomous snakes native to the United States.⁶³ Though only four deaths have been reported in the United States during an 11-year period,⁷⁵ there were two deaths in 2002 from Centruroides scorpion stings; one from the sting and one from complications of antivenom use, both in young children.⁶³ These scorpions hide during the day under wood or in any crack or crevice. Most encounters occur accidentally where the scorpion has hidden inside shoes or other clothes left on the floor or ground.

Centruroides exilicauda venom primarily is neurotoxic and produces few local symptoms. It acts by binding to sodium channels and causing prolonged depolarization of nerve cells. Both somatic and autonomic nerves are affected. Stings do cause immediate local pain, and tapping the sting site dramatically worsens pain. Systemic symptoms of various cranial nerve dysfunction (i.e., double vision, speech problems, etc.) can be seen. Difficulty with secretions can lead to respiratory problems, and motor nerve dysfunction can give focal seizure-like activity. At times, bronchospasm can be seen and confused with asthma. Unfortunately, diagnosis of a scorpion sting is purely along clinical lines. When young children are stung, accurate diagnosis can be challenging. Scorpions are common in areas where black widow spiders are found and, while some symptoms (i.e., pain, adrenergic excess—See section on black widow spiders) can overlap, only scorpion stings will display nervous system dysfunction. Tapping the sting site will not produce pain with black widow spider bites, but does with scorpion stings.

A grading scale for Centruroides exilicauda envenomations similar to that for North American pit viper envenomations has been developed. Grade I denotes only local symptoms, Grade II mild remote symptoms, Grade III adds cranial nerve or somatic skeletal neuromuscular dysfunction, and Grade IV occurs with both cranial nerve and somatic nerve dysfunction. Examples of common cranial nerve symptoms include slurred speech, fasiculations of the tongue, hypersalivation, and abnormal eye movements. Somatic muscle jerking may appear seizure-like, but patients will remain conscious during the events. The most severe cases also may have hyperthermia (up to 40°C /104°F), rhabdomyolysis, metabolic acidosis, pancreatitis, and coagulopathies.⁷⁶ Symptoms usually begin rapidly after envenomation and take roughly 30 minutes to five hours to peak. Most symptoms abate within 9-30 hours, but pain and paresthesias may be present for up to two weeks. Adults are stung more often than children, but Grade IV symptoms are more common in younger children.

Antivenom derived from goats was produced in the past by Arizona State University, but no longer is in production. Limited supplies exist, but only for use in Arizona, and these supplies likely will soon be consumed. The Banner Poison Control Center in Phoenix should be contacted (602-253-3334 or 800-222-1222) concerning use of this antivenom. Although generally given by some practitioners for Grade III and IV envenomations, it is neither FDA approved nor widely recommended. While antivenom will reduce systemic symptoms, it does not appear to reduce pain or paresthesias. When treating with supportive care, realize that some authors suggest avoiding use of opiates with scorpion stings in patients who are not intubated as respiratory depression from opiates can exacerbate the effects of venom on respiratory status. Risks of antivenom use are the same as for other antivenoms: immediate allergic reaction (anaphylaxis) and delayed allergic reaction (serum sickness). A new Centruroides scorpion antivenom (Alarcraryn, produced by Laboratorios Silanes, Mexico City) is undergoing clinical trial in the United States. Those wishing details on Centruroides exilicauda antivenom use are referred to the Arizona Poison and Drug Information Center at (520) 626-6016 or (800) 222-1222, or the Banner Poison Control Center in Phoenix.

Ticks. Ticks are a blood-sucking member of the arachnid family and can be classed as hard or soft based on the type of body covering they possess. Although both types are found in the United States, the hard ticks are they type commonly encountered. Soft ticks are nocturnal and only attach to feed for a few minutes, while hard ticks are active during the day and attach and feed for several days. Ticks climb up on vegetation and wait for animals or people to brush by so they can grab onto a host. Most people only will encounter ticks when they are outside, but theoretically pet animals such as dogs and cats can bring ticks into the house that may release later and then attach to a human.

Tick removal can be difficult and should be performed in the proper way to avoid further contamination. Ticks may be found on the body before they bite. If so, the tick simply can be picked up by forceps. Attached ticks easily can be identified as they have their heads inserted into the patient’s skin. There often is a small inflammatory reaction around the bite. Attached ticks should be grasped as close to the skin surface as possible with a blunt forceps and pulled out with gentle steady pressure. Try to avoid crushing or squeezing the body as it may inject potentially contaminated fluid into the wound. The bite site can be cleaned with soapy water or diluted povidone-iodine after removal. In general, most authors do not recommend prophylactic antibiotics for tick bites, citing meta-analyses that do not support treatment for all tick bites.⁷⁷ Even risk of Rocky Mountain spotted fever (RMSF) or Lyme disease is very low. However, one study of Ixodes scapularis bites did find a lower incidence of Lyme disease (5% untreated vs 0% in treated) in patients treated with one 200-mg oral dose of doxycycline within 72 hours after tick removal.⁷⁷ Such treatment should be considered in Lyme epidemic areas after tick removal.

Tick Paralysis. Ticks are responsible for a wide variety of diseases, both directly from venom some species release during feeding and from acting as vectors for other pathogens. Tick paralysis is a relatively rare, but serious disease that results directly from neurotoxic venom released into the wound during feeding. Fully 43 species of tick worldwide have been noted to cause tick paralysis,⁷⁸ but most cases are in North America and Australia. The majority of U.S. cases are seen in the Pacific Northwest and Rocky Mountain areas. As one would expect, tick paralysis is most common in the spring and summer months when ticks are most active. More cases are seen in children than in adults, with younger girls affected twice as often as boys. Symptoms of tick paralysis begin 5-6 days after the tick attaches, and develop as an ascending flaccid motor paralysis, similar to Guillain-Barré syndrome, botulism, and myasthenia gravis. Children may present with ataxia, and respiratory paralysis can develop in only two days. As in most cases of envenomation, laboratory studies (i.e., complete blood count, cerebrospinal fluid) are normal as there are no specific tests that establish the diagnosis. Finding and removing the tick is both diagnostic and curative. A thorough search of the scalp and other areas ticks tend to attach is essential when tick paralysis is suspected.

Tick as Vectors of Disease. Ticks are second only to the mosquito in terms of the number of pathogens vectored to humans. Ticks are responsible for at least six diseases they transmit as vectors. Colorado tick fever is the only viral example (in the United States). Borrelia spirochetes cause Lyme disease and relapsing fever, Rickettsia cause RMSF and Ehrlichiosis, and Babesiosis is caused by a protozoan.

Colorado tick fever occurs when the Colorado tick fever virus is injected into humans instead of its natural rodent host. Although usually self-limiting, complications of encephalitis, pericarditis, myocarditis, hepatitis, and pneumonitis with a few deaths have been described.⁷⁹ Treatment is supportive, but symptoms may take three weeks (or longer) to resolve.

Lyme disease was named for the Connecticut town where it first was diagnosed and is probably the most widely recognized tick-borne infection. Caused by infection with Borrelia burgdorferi after bite by the deer tick Ixodes scapularis, Lyme disease can be difficult to diagnose. It has been documented as far west as Wisconsin and even has similar syndromes seen in Europe, Asia, and Australia. The first clinical phase is caused by the initial injection of the spirochetes. It is characterized by the rash erythema migrans, which usually occurs at the tick bite site within 7-10 days after inoculation. The second stage occurs in days to weeks, is caused by dissemination of spirochetes into the bloodstream, and is characterized by arthritis, fevers, and lymphadenopathy. The third phase occurs a year or more after infection and is a result of sequestration of the spirochetes in the body, usually in the skin, joints, and nervous system. Chronic arthralgias occur often in the large joints (knees). Debilitating central nervous system complications (i.e., spastic paraparesis, ataxia, and cognitive impairment) are common. Cardiac complications (atrioventricular conduction block) also are seen. The only true diagnostic test is detection of antibodies to B. burgdorferi, but this may take 3-6 weeks to become detectable. Treatment can be accomplished with a variety of antibiotics, such as tetracycline (250 mg PO QID), erythromycin (30 - 50 mg/kg/day PO divided QID), doxycycline (100 mg PO BID), amoxicillin (500 mg PO TID), or cefuroxime (500 mg PO TID) for 2-4 weeks. Treatment length varies with the phase of the disease. Currently the FDA has approved a vaccine for Lyme disease, but it is recommended only for patients 15-65 years of age in highly endemic areas.

Relapsing fever is another tick-borne disease caused by Borrelia species. As the name suggests, recurrent fevers occur lasting around three days with variable duration of time between episodes. The fevers occur from cycles of bacteremia. Diagnosis is made by finding spirochetes on a peripheral blood smear stained with Wright-Giemsa stain during a febrile episode. Treatment is either erythromycin or tetracycline.

Rocky Mountain spotted fever (RMSF) remains the most common fatal tick borne disease in the United States. Although the association with the Rocky Mountains was true in the early 1930s, today most of the cases of RMSF are found in the southern and eastern United States, making the name a bit misleading. Several tick species carry and transmit Rickettsia rickettsii, the causative organism for RMSF, and currently the group with the highest incidence of the disease is 5-9 year olds living in the mid-Atlantic and southern United States. Ticks usually have to stay attached for only 6-10 hours to transmit the bacteria. Incubation times vary from 2-14 days, with the more severe cases having the shortest times. A variety of symptoms develop, but the classic presentation is fever, headache, rash, and history of tick bite. Fever usually is higher than 102.2°F (39°C), but the most characteristic feature is the rash. The rash appears as a result of capillary and small blood vessel vasculitis. It initially blanches, but after 2-3 days the lesions are petechial and may coalesce. The rash classically starts on the wrists, hands, ankles, and feet and then progresses proximally to cover the entire body. While the rash is pathognomonic, it may be absent in up to 15% of cases.⁷⁸ Meningitis, myocarditis, adult respiratory distress syndrome (ARDS), disseminated intravascular coagulation (DIC), and acute renal failure are the most serious complications. Definitive diagnosis is made by detecting rising antibody titers to the bacteria. Treatment is with tetracycline or chloramphenicol. Even with antibiotic therapy, the mortality remains at 5%. Most fatal cases can be traced to delay in diagnosis and treatment.

Ehrlichiosis is a less well-known Rickettsial disease. Most cases are seen in the summer months. Often a disease of animals (i.e., dogs, horses, sheep, goats, and deer), the human ehrlichiosis varies from mild viral-like infections to life-threatening conditions. The more severe cases occur in elderly or immunocompromised patients with respiratory failure, encephalitis, renal failure, and gastrointestinal bleed as the common causes of death. Like RMSF, ehrlichiosis is a clinical diagnosis most often made by admitting physicians. Doxycycline and tetracycline are effective treatments.

Babesiosis is another disease vectored by ticks, however the pathogen here is a protozoan. Babesiosis primarily is seen in small outbreaks in Cape Cod, New York, and Rhode Island. It is similar to Lyme disease in that it is carried by mice and white-tailed deer. The primary clinical features are fever, myalgias, and other constitutional symptoms. The disease can be severe and may last for weeks without antibiotic treatment (clindamycin and quinine). Patients with previous splenectomy are at higher risk for the severe symptoms.

Hymenoptera (Bees, Wasps, and Ants). Bees and Wasps. The number of envenomations by bees and wasps is second only to fire ants. Bees and wasps can form social colonies (hives) and act in unison to protect the hive when only one individual is threatened. Though bees and wasps sting an estimated 1 million people per year in the United States, only 30-120 people per year die as a result. Wasp venom tends to cause severe reactions in more cases than does bee venom. As the amount of venom in each sting is relatively small, most deaths occur from allergic reactions rather than by direct effects of the venom itself. It is estimated that it takes about 50 bee stings for systemic signs of envenomation, and roughly between 500-1000 stings for a fatality.⁸⁰ Research is being done on antivenom, but none is currently available. Solitary bee or wasp stings without allergic reaction are only dangerous when they occur in the mouth or pharynx, typically taking place when one drinks from an open soft drink/beer and accidentally swallows the insect. While native North American bee and wasp venom alone is not normally dangerous, Africanized bees ("killer bees") can live up to their name.

Africanized bees have larger hives, swarm more often, and fly farther distances than North American bees. Only female bees have stingers, and can sting only once as the stinger detaches from the bee during the sting eviscerating the insect. The Africanized bees’ most dangerous habit is that they attack in large numbers and chase people much farther from their hive than American bees do. Initially hybrid African and North American bees escaped from Brazil in the late 1950s and first arrived in the United States in 1990. They now are found in many of the southern states with the greatest populations in Texas, Arizona, and California. With no natural predators, it is predicted that Africanized bees eventually will inhabit all of the southern United States. While they do not have more potent or more allergenic venoms than American bees, they do sting up to 10 times more than European bees do.⁸¹ While no deaths were reported by the AAPCC in 2002,⁶³ Africanized bees have killed more than 350 people worldwide, with about 10% of these occurring in the United States. However, bees of both varieties can fly at a speed of only about 4 mph, allowing most people with normal mobility to escape.

The primary ingredient in bee venom is melittin, which comprises 50% of bee venom by dry weight. Melittin damages cell membranes through detergent-like action, and causes degranulation of basophils. Other components of bee venom cause direct histamine release from mast cells, and histamine also makes up 3% of the dry weight of bee venom.⁸¹ Serotonin and acetylcholine found in the venom are largely responsible for the immediate pain stings produce.

Wasps may look similar to bees at first glance, but they are very different insects. While bees feed on pollen they carry back to the hive, wasps are carnivorous. Thus, while bees use their sting only for defense and can sting only once, wasps use their sting to capture prey and can deliver multiple stings for defense. While several hundred stings are necessary for envenomation from bees to be dangerous, only 40-50 stings from certain wasps (white face hornet) can be lethal.⁸¹ Similar to bees, only the female wasps possess stingers. Bee stings occur throughout the summer, but wasp stings tend to occur in late summer and early fall when they become more territorial around their nests. While bees build hives in hollow trees or rock crevices, wasps often nest closer to the ground in tree stumps or in animal burrows. Wasps also defend their nests when disturbed, and attacks often occur when nests are disturbed accidentally by lawnmowers. Hornets are a type of wasp that build larger nests housing thousands of individuals and often are found in trees. Bees may be attracted to perfumes, but wasps are attracted by certain meats, fruit, and sweet drinks.

Local Reactions. Bees and wasps produce similar clinical effects when they sting, which can be divided into local and systemic effects. Both cases can have allergic components. Local effects are well known to anyone who has ever been stung: immediate pain, edema, redness, and itching in some cases (from histamine release). Most swelling and pain from local reactions usually resolves spontaneously in two days. Frequently, the bee’s stinger will be observed still attached to the site. In the past it was recommended that the stinger must be scraped off and not removed with forceps as the venom sac attached to the stinger might be squeezed and increase the amount of venom injected. A recent study showed no difference whether the stinger was removed by forceps or by scraping.⁸² It is important to remove the stinger and venom sac as quickly as possible by whatever means, as the sac will continue to pump venom into the skin for up to one minute after the rest of the bee no longer is attached.

The amount of local swelling varies significantly from person to person, and it is not unusual for local swelling to spread more than 15 cm away from the sting. These patients with larger than normal local reactions still are not considered high risk for systemic allergic reactions,⁸¹ but likely will continue to have exaggerated local reactions in the future. In some cases, these large local reactions are misdiagnosed as cellulitis.⁸³ Wasp or bee venom (or any venom for that matter) generally does not carry bacteria and thus stings and bites are not particularly high risk for cellulitis. Given that infection still can occur, there are several points that can be useful to differentiate local histamine-mediated response from cellulitis. (See Table 6.)

In most cases of cellulitis, symptoms are progressive and usually respond to antibiotic therapy. Thus the history of cellulitis would be a slowly enlarging area of redness that is more painful with time. Allergic reactions tend to rapidly develop and then stop spreading. Allergic reactions also have less pain and more itching; they are generally not tender to touch. While they appear red, they also are not very warm to touch as one would expect for cellulitis of the same size. Many patients with a large cellulitis may have fever and an elevated white blood count (WBC) but this typically is not the case for allergic reactions. Lastly, patients with a history of similar allergic reactions to bee or wasp stings in the past are more likely to have a reaction other than cellulitis.

Systemic Reactions/Anaphylaxis. Serious allergic reactions to bee and wasp stings are not that rare in the United States. It is estimated that 0.4% of the U.S. population shows signs of allergy to insect venoms,⁸¹ and that 40-50 deaths occur annually from fatal anaphylaxis.⁸⁴ Most victims of anaphylactic reaction to bee or wasp sting are adults rather than children. There is no correlation between the severity of the systemic reaction and the number of stings. Systemic symptoms from allergic reaction to bee or wasp stings include flushing, generalized itching and hives, angioedema, respiratory distress, wheezing, stridor, chest pain, anxiety, and syncope. The more rapid the reaction, the more dangerous it may become. Fully 70% of severe reactions occur within 20 minutes, 90% occur within 40 minutes, and 100% occur in fewer than five hours.⁸⁵ Though biphasic anaphylaxis is reported with other causes (foods, drugs) these reactions are rare with insect stings.⁸⁵ It is believed that anaphylaxis is an IgE meditated response; following a sting there is an increase in the IgE antibody production.⁸⁶ Fatalities usually occur in the first hour after a sting, and usually result from airway obstruction, hypotension, or both. Though fatal reactions can occur as the first reaction, most will follow a previous mild generalized reaction. The shorter the interval between stings, the more likely a severe reaction will take place. While this is true, there is no relation between risk of systemic reaction and the number of stings in the past.⁸⁷ Further history of an anaphylactic reaction does not always predict a future reaction either. In one study, only 99 of 138 patients had a second anaphylactic reaction in response to a bee/wasp sting, while 22 had more mild reactions, and 17 had more severe responses than the first case.⁸⁸ Unfortunately, there is no reliable method by which to screen the population for propensity of anaphylaxis to bee/wasp venom. Skin testing with bee/wasp venom is the most reliable method, but will not identify all patients.

Treatment for anaphylaxis is standard and not based on the source of the reaction. Epinephrine (1:1000) subcutaneously is the first line of treatment: 0.3-0.5 mL for adults, and 0.01 mL/kg (maximum dose 0.3 mL) for children younger than12 years. Massaging the injection site is reported to speed absorption of subcutaneous epinephrine. Epinephrine and albuterol nebulized treatments can be effective for respiratory distress. Hypotension can be treated with epinephrine infusion (1 mg in 250 mL or 4 mcg/mL, starting at 1 mL/min and increased to support BP). Intravenous fluids and pressors such as dopamine also can be used. The H1 blocker diphenhydramine (diphenhydramine 25 mg to 50 mg IV), the H2 blocker ranitidine 50 mg IVPB, and corticosteroids (methylprednisolone 125 mg IV or 2 mg/kg for children) also are first-line therapy. Airway obstruction from edema may not respond rapidly enough to medical treatment, and one should be prepared to perform cricothyroidotomy early for patients where standard intubation maneuvers fail. Even if rapid recovery of anaphylactic symptoms is achieved, patients still should be observed for 24 hours.

Prior to discharge, any patient treated for systemic symptoms from a bee/wasp sting should be prescribed an epinephrine self-injector (0.3 mg EpiPen) as the next sting may be more severe. Patients should carry the self-injector with them at all times, and wear medical alert tags. When confronted by flying hymenoptera, patients should try to remain calm and retreat slowly.⁶⁴ If patients are stung and use their self-injector, they still are advised to seek medical attention as one dose of epinephrine may not always stop anaphylaxis.⁸⁶ Patients also should be educated on prevention and avoidance of stings and be referred for skin testing and possible desensitization. Referral to an allergist is important as 60% of patients who experience systemic reactions continue to have future allergic reactions.⁸⁶ Immunotherapy from whole body or venom extracts has been found to desensitize patients and are 97% protective in subsequent stings.⁸⁹ Immunotherapy given over a five-year course provides lasting protection even after stopping the therapy. In children, effects have been noted 10-20 years after the discontinuation of immunotherapy.⁹⁰ Prevention and avoidance discussions should include information regarding destruction of nests; wearing shoes, tight-fitting and long-sleeved shirts and pants; avoidance of bright colors and floral patterns; use of unscented cosmetics, hair products, and detergents; use of cotton gloves for yard work; caution when in common sting locations, such as orchards, picnics areas, and outdoor restaurants; cleaning garbage cans; and avoidance of yard activities if severely allergic.⁹⁰

Fire Ants. While there are many species of ants in the United States, only the fire ant tends to be clinically significant. Fire ants probably account for more envenomations in the United States than all other envenomations combined. It is estimated that fire ants sting more than 9 million people per year. There actually are three species that are native to the United States, but it is the imported red fire ant that causes most of the damage. These ants are thought to have arrived in this country in the 1930s aboard a ship that docked in Mobile, Alabama. Since then, they have spread throughout the Southeast and continue to move northward. Fire ants make large mounds in the soil that are familiar to anyone who accidentally has stepped on one. The ants rush out of their nest when disturbed and swarm over any body part they can reach. Once one ant begins to sting, it releases a pheromone that excites the other ants, inducing all the ants to attack simultaneously. Fire ants have a stinger located in their abdomen similar to bees and wasps. They grab the skin with their mandibles, arch their bodies, and if not removed continue to circle around their mandibles stinging in a circular pattern. Their venom produces an immediate burning pain (hence the name fire ant), and also is highly allergenic. Pain from the bite eases in 30-60 minutes, as does the wheal produced. A sterile pustule forms in 1-2 days, which normally will heal without treatment. The true danger of the bite is an acute allergic reaction. Anaphylaxis is not rare after fire ant sting, and 32 cases of fatal anaphylaxis have been documented. (See previous section on anaphylaxis in bees and wasps.)

Caterpillars. Of the 140,000 species of caterpillar that are found, only 50 in the United States are capable of stinging. The pus caterpillar (or asp) is the most dangerous U.S. species, and is found primarily in the Southeast but can be found as far north as Maryland. All caterpillars only possess venom for defensive purposes. They have spines over their surface that are hollow with venom glands at their base. Many species are brightly colored to advertise their potential for harm. Caterpillars only sting when they come into contact with bare skin, and in most cases the contact is accidental. Two general patterns of caterpillar envenomation occur. Puss caterpillars are an example of the first. Immediate pain followed by redness and swelling occurs, but in some cases systemic reactions are possible. Hypotension, shock, respiratory distress, vomiting, fever, headache, and lymphadenopathy all have been reported.⁹¹ The second type of reaction is more delayed with little or no immediate pain felt. Several hours or even 1-2 days later an itching urticarial rash develops at the site and may last up to one week. Spines that have detached from the caterpillar still are capable of producing this reaction. Though usually self-limiting, serious complications have occurred when the spines lodge in a patient’s eye. Treatment is limited to symptomatic care only.

Centipedes. Centipedes and millipedes often can be confused as they have a similar body design. Both are flattened, elongated arthropods whose bodies are divided into segments. Both centipedes and millipedes possess legs on each body segment, but millipedes have two pairs of legs per segment, while centipedes have one pair. Centipede legs tend to be larger and they also have a pair of caudal appendages on the last body segment, where millipedes do not. Millipedes generally are slow-moving vegetarians that curl up in a ball when disturbed, whereas centipedes are carnivorous, fast-moving, and have fangs used both for hunting and defense.

Centipedes typically are nocturnal and spend the daytime under rocks and in crevices. Centipedes are venomous and inject venom through their bite only. Fortunately, centipede bites are only painful, and even throughout the world deaths are very rare. Several species of Scolopendra are found throughout the southern United States, and bites produce several symptoms. These include local pain, which can be severe; redness; lymphadenopathy; and lymphangitis. Systemic symptoms are mild and include headache, palpitations, nausea, or vomiting. Local necrosis can occur and usually is mild, however rare case reports exist of more serious reactions. Treatment is purely symptomatic and usually centers on pain relief. Local anesthetic blocks can be helpful to relieve pain as well. Pain can last for days, but typically does not persist longer than several weeks.

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