Travel Medicine: The Latest on Pre-Travel Information

Conference Coverage

Editor’s Note: The following represents a selection of clinical papers summarized by David O. Freedman, MD, presented at the annual meeting of the American Society of Tropical Medicine and Hygiene, held in Baltimore, December 1-5, 1996. Data are abstracted both from the published program book and from the presentations themselves. For more information on the following material, contact astmh@ripco.com —scd

Malaria

Increasing information on atovaquone and proguanil (to be sold under the name Malarone) as a fixed-dose combination in a ratio of 2.5:1 for the treatment of falciparum malaria is emerging rapidly. Several trials have already been published, and at a symposium in Baltimore, composite results of seven different controlled clinical trials, one of which enrolled children, were presented. Using a regimen of 1000 mg atovaquone/400 mg proguanil once daily for three days, an overall cure rate of 98.5% in 452 evaluable patients was reported. The studies took place in Thailand, Gabon, the Phillipines, Zambia, Kenya, Brazil, and France. Adverse events were mostly gastrointestinal. Only patients with uncomplicated malaria were evaluated. Very few data on efficacy in vivax malaria are available, though one presented study showed a high rate of recurrent parasitemia at 14 days. Whether this represents relapse or recrudescence of resistant parasites was unclear. Case reports show efficacy against P. ovale and P. malariae.

The first field trial conducted to determine the efficacy and safety of Malarone as a suppressive prophylactic agent against P. falciparum was reported from a highly endemic area of Kenya. During the 10-week suppressive prophylactic period, the combination of atovaquone and proguanil (in doses as low as 250 mg/100 mg) was 100% efficacious as compared to less than 50% efficacy in the placebo group.

Malarone has recently been licensed for use in P. falciparum treatment in the United Kingdom. The manufacturer stated at the symposium that they will seek licensure in the United States only when they have enough data to apply for indications for both treatment and prophylaxis. This will likely be later in 1997. Because the efficacy against vivax malaria is unclear at the present time, I would hope that this is sorted out quickly. Clearly, a prophylactic drug that didn’t work against vivax would have much more limited utility.

A commercial dipstick test (Parasight-F) for falciparum malaria that detects P. falciparum-specific, histidine-rich protein in blood samples was the subject of much discussion at a symposium on malaria diagnosis. Several published reports from malaria-endemic areas had already reported sensitivity of 100% at all but the lowest (< 20 parasites per microlitre of blood) parasitemias. The technique appears to be equally sensitive and specific in diagnostic laboratory tests in the developed world, according to a report from the London Hospital for Tropical Diseases. The major drawback of this and several competing rapid tests, that would even be suitable for office use, is that they are non-quantitative and that they only detect P. falciparum and not other species of malaria. So a positive test is very helpful, but a negative test would still have to be followed by a conventional smear.

Gnathostomiasis in East Africa

Infection with the nematode Gnathostoma spinigerium has generally been thought to be restricted to Southeast Asia and a few foci in South America. Wolfe et al reported the first cases of gnathostomiasis from Africa. Five American tourists visiting the Selous Game Reserve in Tansania presented with migratory, painless, subcutaneous nodules a few months after eating sushi from catfish they had caught on their trip. Serology was positive in all cases and in one individual, a live larvae was isolated and identified at the Armed Forces Institute of Pathology.

Leptospirosis

In October 1995, a large outbreak (at least 2300 suspected cases) of leptospirosis associated with pulmonary hemorrhage occurred in Nicaragua. Two papers, one from the Centers for Disease Control and Prevention in Atlanta and one from a Yale medical resident who happened to be doing an elective in the affected area at the time, presented fascinating perspectives on the outbreak. Because pulmonary hemorrhage as a consequence of leptospirosis had only been reported previously from Asia, but never from the Western Hemisphere, local physicians first suspected dengue, then yellow fever, arenavirus infection, hantavirus, and even Ebola. Leptospirosis was finally identified by immunohistochemistry of lung tissue from autopsy specimens when fatalities began to occur. Human isolates were found to be of both the Canicola and Pyrogenes serogroups. Precipitation records showed four times the expected rainfall in the two preceding months. Dogs may have played a role in amplification of the epidemic. The reason why pulmonary manifestations of leptospiral infection have not previously been seen in the Western Hemisphere remains obscure. Serologic screening for leptospirosis should be considered in the workup of any undifferentiated febrile illness.

Traveler’s Diarrhea

The epidemiology of traveler’s diarrhea varies in different parts of the world and it is always helpful to keep up with current trends at popular destinations when advising travelers. In a culture survey of five hotels in Negril, Jamica, specimens from 316 subjects with traveler’s diarrhea were analyzed. An enteropathogen was identified in 112 (35%) subjects studied: enterotoxigenic E. coli in 85 (26%); Salmonella in 15 (5%); Shigella in 10 (3%); C. jejeuni in 4 (1%); Giardia in 3 (1%); and cryptosporidium, Aeromona, and Plesiomonas in one isolate each. In the hotels with the greatest number of cases, diarrhea characteristically occurred in multicase, presumably foodborne, outbreaks.