By Carol A. Kemper, MD, FACP
Pasteurellosis Suspected in Asian Elephant Deaths
Officials suspect hemorrhagic septicemia (HS) from pasteurellosis as the cause of the sudden and unexpected deaths of six elephants within a two-week time period at the Karlapat Wildlife Sanctuary in Odisha, India. The deaths began Feb. 1, 2021, when the carcass of a 38-year-old pregnant jumbo was found. The most recent death was a small calf. Karlapat Wildlife Sanctuary is a 68-square-mile preserve located in the Eastern Highland region of southern India and is a popular tourist destination. It also is an important agricultural area, and farmers often allow their cattle to graze in the moist deciduous forests of the preserve. Samples of water from the preserve are being examined, with plans to disinfect contaminated water sources.
Cattle and other ungulates are susceptible to Pasteurella multocida and Pasteurella haemolytica, which cause bovine respiratory disease (BRD) (sometimes referred to as shipping fever), especially when the animals are under stress. Symptoms may range from sniffles to fever, cough, and pneumonia. Occasionally, more virulent strains cause HS, a rapidly fatal infection. Generally, these organisms are nasopharyngeal commensals, and they live in the mucosa and tonsils (or elephant trunks) and can contaminate forest wetlands and water supplies.
It has been postulated that climate change may result in more of these outbreaks in grazing animals, with higher temperatures and brackish water. Several manufacturers produce vaccine for BRD, either as a single vaccine or often combined with other bacterial vaccines, such as Clostridium chauvoei. One wonders how large a BRD vaccine would be required to vaccinate an elephant (the equivalent of a “horse pill”), although elephants can receive tetanus and rabies vaccine, and there are efforts to create a vaccine for endotheliotropic herpesvirus in Asian elephants.
Of course, we know Pasteurella as zoonoses, generally caused by the bites of cats and dogs, but ungulates are considered especially vulnerable when larger numbers of bacteria are spread in oral or nasal secretions or contaminate water supplies. I was curious about why elephants are considered ungulates, since they are not hoofed but have toenails, much like humans (albeit larger). Elephants are part of a larger group of animals adapted to living on grasslands that walk on their toes (digitigrade), although other ungulates evolved a single hoof (horses and zebras) or two hooves (goats and hippopotami) from one or two toes. Like these animals, elephants walk on the tips of their toes, but they never evolved hooves. For this reason, some consider them “sub-ungulates” or “near-ungulates.”
I was surprised to learn that “ungulate” is a much disputed taxonomy — and it is argued whether the current placement of even-toed hoofed mammals (e.g., cattle, buffalo), odd-toed hoofed mammals (horses, zebras), and Proboscidea (e.g., elephants and manatees) is evolutionarily correct or a taxonomical convenience. One expert said ungulate is “the most abused term” and likely involves several independent lineages that developed similar features (evolutionary convergence). In a curious twist, dolphins are considered ungulates, having evolved from even-hoofed animals, although their toes have long ago receded.
Negative-Strand Testing for COVID-19
These authors from Stanford University in Palo Alto, CA, described the results of two-step strand-specific RNA polymerase chain reaction (PCR) testing to the envelope gene of SARS-CoV-2 in a large group of patients. As we all know, real time RT-PCR cannot distinguish between inactive molecular material and replicative-competent virus in the nasopharynx. Cycle threshold (CT) values have been used as a “down and dirty” gauge of the amount of virus present in a swab specimen, as a marker of infectivity. However, actively replicating virus produces minus-strand RNA intermediates, which can be measured.
A total of 146 patient specimens were tested, including a retrospective convenience sample of 93 clinical specimens from inpatients and outpatients collected March-April 2020, and 53 prospectively collected research specimens from patients with confirmed SARS-CoV-2 infection July-September 2020. The median age was 50 years (range, 36-63 years), and half were women; 25% were obtained from patients cared for in intensive care, and 20.5% were from immunocompromised persons. Specimens were collected a median of nine days after symptom onset (range, -1 day to 42 days).
Minus-strand RNA was detected in 41 persons (28.1%), for which information on the date of symptom onset was available in 38. The ratio of minus/positive strand RNA varied by patient, but minus-strand RNA was detected from 25 patients at 0-7 days, four patients at 8-14 days, and six patients > 14 days after symptom onset (three outliers were removed from the analysis). Minus-strand RNA was detected in seven prospectively collected specimens, including two non-immunocompromised patients at day 11 and another at day 12, one of whom had been asymptomatic for 48 hours. Three of these seven patients were immunocompromised; minus-strand RNA was detected at 18 and 30 days in one patient with persistent fever, and 26 days in another. The median cycle values were significantly lower in persons with detectable negative-strand RNA compared to those without (median CT value 20.7 vs. 33.2, P < 0.01). Interestingly, while 26/146 (17.8%) persons were considered immunocompromised, only 6/41 (14.6%) patients with detectable minus-strand RNA were immunocompromised.
Although the mandatory quarantine period for persons with SARS-CoV-2 infection initially was 14 days, this has been reduced in some states to 10 days. These data suggest that at least two persons without immunocompromise had detectable minus-strand RNA > 10 days following symptom onset. Although this guidance may be reasonable for most COVID infections in the community, whether it is similarly applicable to the acute care environment, where patients have more significant underlying disease and critical illness, is less obvious. For this reason, I have advocated our facility to apply a general 21-day rule for all hospitalized persons with persistent symptoms. While this requires added use of isolation rooms and personal protective equipment, it is easier to operationalize than having infection prevention personnel combing through charts trying to assess who may be “immunocompromised” or more ill. Strand-specific RNA testing could add a layer of confidence to removing isolation precautions and allow patients to proceed more safely with medical procedures.