ASTMH Abstracts of Interest

Abstracts of the 53rd Annual Meeting of the American Society of Tropical Medicine and Hygiene, Miami Beach, Florida November 7-11, 2004. J Am Soc Trop Med Hyg. 2004; 71:Supplement. # refers to abstract number.

Malaria

#331. Duong S, et al. Current Malaria Situation in Cambodia. The number of malaria cases decreased from 170,000 in 1997 to 111,000 in 2002, but increased to 133,000 cases and 492 deaths in 2003. The mortality rate was 3.7/100,000 cases in 2003, and case the fatality rate for severe malaria was 10%. The ratio of P. falciparum to P. vivax was 7:1. Duong et al commented that the 2003 data may represent a number of factors: improvement of public health facilities in remote areas, movement of people into high-risk areas, decline of control measures, emergence of drug resistance, and inconsistencies in diagnostic criteria. The study did not suggest any major change in malaria epidemiology or drug resistance. Travelers to Cambodia should continue to be prepared for malaria transmission, according to existing guidelines that indicate malaria risk throughout the country except for Phnom Penh. Also, parasites may be resistant to mefloquine near the border with Thailand.

#586. Kasili S, et al. Field Trial of 5 Repellents Against Wild Mosquitoes in Ahero, Kenya. Twelve human volunteers tested 4 insect repellents, Avon’s SS220 spray, SS220 lotion, Bayrepel lotion, and S.C. Johnson’s Autan Bayrepel lotion against a DEET control in western Kenya. All repellents succeeded in protecting through the 12.5-hour nightly test periods conducted in May 2004. If additional studies using more subjects could confirm these findings, alternative repellents might be available as part of personal protection measures against malaria and other vector-borne diseases.

#712. Noedl H, et al. ELISA: Augmenting the Gold Standard in Malaria Diagnosis. Seven hundred blood samples were tested for P. falciparum using a commercially available ELISA antigen detection assay, based upon histidine-rich protein 2 (HRP-2). The sensitivity of the test was 98.8% and the specificity was 100%, exceeding those of expert microscopy. Possible use of this test includes complementing microscopy for epidemiological field research, confirming microscopic diagnosis, and screening for blood banking. The test may be useful in travel medicine in assessing the exposure of travelers to P. falciparum, and to supplement microscopy in the diagnosis of suspected cases.

#713. Causer LM, et al. Malaria Diagnosis and the Role of Diagnostics: Implications For Malaria Drug Policy. An assessment on the prevalence of malaria parasitemia using exit interviews and malaria smears was conducted on outpatients who visited 3 hospitals, 4 health centers, and 9 dispensaries in rural Tanzania in 2002. Data showed a parasite prevalence of 25%. Among patients with clinical diagnosis of malaria, 66% had no malaria parasites on blood smear. Modeling of the impact of microscopy and rapid diagnostic tests could reduce over-diagnosis of malaria by 91% and 99%, respectively. These results demonstrate its frequent over-diagnosis in developing countries. Travelers should be advised regarding malaria over-diagnosis in order to avoid missing other treatable causes of illness, and minimize the inclination to discontinue malaria chemoprophylaxis.

#747. Pacha L, et al. Reemergence and Persistence of Vivax Malaria in the Republic of Korea. The study identified all reported malaria cases in Korean civilians, military, and US soldiers from 1993-2003. Republic of Korea (South Korea) experienced a reemergence of P. vivax since 1993, which peaked in 1997-2000 and subsequently declined. Interviews of 68 military cases indicated that exposure occurred within 25 km of the Demilitarized Zone, but 1 case was attributed to a training site 35 km south of Seoul.

Epidemiology of Infections

#161. Cabada M, et al. Etiology and Impact of Traveler’s Diarrhea Among Tourists to Cuzco, Peru. Fifty-three travelers who consulted 3 study physicians in Cuzco, Peru, between August 2003 and April 2004 for TD, were enrolled in a study to assess the causative pathogens. The majority of the travelers were from Europe. Sixty-two percent of subjects had at least 1 pathogen present in the stool, and 27% of these had more than 1 pathogen. Blood in the stool was associated with finding a pathogen. The most common pathogens identified were enterotoxigenic E. coli (ETEC, 27.3%), enteroaggregative E. coli (EAEC, 21.2%), Cryptosporidium (12.1%), and Campylobacter jejuni (9.1%). Sixty percent of the C. jejuni were ciprofloxacin-resistant. Findings of the study are consistent with others that have shown ETEC and C. jejuni to be common causes of TD. In addition, Cryptosporidium appears to be a frequent cause, and EAEC may be an emerging pathogen.

In addition to the importance in identifying etiologies of fever in the local population, a number of studies demonstrate the epidemiology of infectious diseases that are useful in the evaluation of febrile returning travelers:

#501. Pachas PE, et al. Spotted Fever Group Rickettsial Diseases Associated With Leptospirosis in Pomabamba, Ancash Department, and Peru. Sera from 49 subjects with petechiae or fevers of unknown origin who presented in June 2003 were tested by IFA for antibodies to spotted fever group rickettsia (SFGR), typhus group rickettsia (TGR), and IgM against Leptospira. Fourty-one percent were positive for SFGR, 2% positive for TGR, and 33% were positive for Leptospira; 33% tested positive for both SFGR and Leptospira. Although the species of Rickettsia still needs further identification, SFGR and leptospirosis appear to be emerging diseases from Peru.

#503. Jordan G, et al. Evidence of Murine Typhus Cases in Northern Peru. Sera from 115 patients with suspected dengue fever from Tumbe, in northern Peru, were tested for dengue, yellow fever, Venezuelan equine encephalitis, Oropouche, Mayaro viruses, Leptospira, Brucella, SFGR, R. typhi, and Coxiella burnetti. Fifteen (13%) were confirmed to have R. typhi, and illustrated that murine typhus causes a significant number of cases clinically, resembling dengue fever in this area.

#556. Zavaleta C, et al. Acute Febrile Illnesses in Yurimaguas, Peru 2000-2004. Three hundred twenty-four subjects with acute febrile illness were tested by serology and/or viral isolation for dengue, yellow fever, Venezuelan equine encephalitis, Mayaro, Oropouche viruses, Brucella, Leptospira, Coxiella burnetti, SFGR, and R. typhi. Virus isolation confirmed dengue in 25 patients and VEE in 1 patient; serology identified additional cases. Dengue was the leading cause of fever identified in this study (17%), followed by SFGR (7%), leptospirosis (7%), Q fever (5%), VEE (1%), R. typhi (0.9%), Oropouche (0.6%), yellow fever (0.6%), and Mayoro virus (0.3%).

#545. Punjabi NH, et al. Cholera As An Important Cause of Diarrheal Outbreaks in Indonesia: A 10 year Observation. Outbreaks of diarrhea in Indonesia were investigated between 1993 to 2002. Eighteen investigations were done, and 17 of them yielded V. cholerae 01 biotype El Tor serotype Ogawa in 214 of 1788 specimens tested. Stool specimen from a 1994 outbreak in West Kalimantan identified V. cholerae 01 biotype Inaba, which resulted in overall isolation rate of 12.3% for V. cholerae 01. The last investigation in 2002 in West Timor identified rotavirus type 1.

#649. Garcia-Rivera EJ, et al. Differential Diagnosis of Dengue-Like Illness in Puerto Rico. Sera from patients with dengue-like illness from 1999 to 2001, who were negative for dengue antibodies, were tested further for leptospirosis, measles, rubella, hepatitis A and B, influenza, rickettsial diseases, and parvovirus B19. Thirty-two percent of the patients were seropositive for another disease. The leading positive studies were influenza (seroconversion), measles, rickettsioses (seroconversion), leptospirosis, and parvovirus B19. Influenza should be considered routinely in febrile returning travelers.

Vaccines

#162. Kirkpatrick BD, et al. A Novel Oral Typhoid Vaccine is Safe and Immunogenic in 2 vaccine presentations. A new single dose of oral typhoid vaccine, called M01ZH09, was prescribed. Thirty-two human volunteers received the vaccine, and demonstrated positive IgA antibody assay (88-93%) at day 7, and IgG seroconversion of 73-81% on day 14 and 28, respectively. The vaccine appears to be well tolerated and immunogenic. The currently available oral typhoid vaccine consists of 4 capsules taken on alternate days, which is associated with lack of adherence. The single dose vaccine would greatly improve the ease of administration and compliance. The duration of protection would need to be elucidated.

#203. Nothdurft HD. Combined Vaccination Against Hepatitis A and Typhoid Fever. Seven hundred fifty subjects studied for antibody levels following a combined hepatitis A and typhoid fever vaccine showed protective levels 14 days after injection, 95.6% against hepatitis A and 86.4% against typhoid. Since the epidemiology of hepatitis A and typhoid fever are similar and associated with food and water hygiene factors, the 2 vaccines are often administered together for travelers. A combined vaccine would reduce the number of injections and would be attractive to travelers.