Passport to Montreal— 6th Conference of the International Society of Travel Medicine
Special coverage
Nearly 2000 participants gathered in montreal, québec, for the 6th Conference of the International Society of Travel Medicine. These meetings included plenary sessions on malaria and vaccines, symposia and workshops on all aspects of travel and migration medicine, cases of the day, and the "voices of the host countries"—all amid free communication sessions and posters that were on view for most of the meeting. This rich and varied conference was attended by each of our associate editors who have collaborated to summarize some highlights of those presentations. —fjb
Opening Plenary Session—Malaria
Reviewed by Philip R. Fischer, MD, DTM&H
Chairpersons: AEC Rietveld, WHO, Geneva, Switzerland, and Mary Wilson, Mount Auburn Hospital, Cambridge, MA.
New Antimalarial Drugs for Chemoprophylaxis—Dennis Shanks, U.S. Army Medical Research Unit, Nairobi, Kenya.
The opening plenary session of the 6th Conference of the International Society of Travel Medicine focused on malaria. Participants were treated to an entertaining and scholarly review of the latest information about chemoprophylaxis, diagnostic testing, and vaccines. Dennis Shanks, an American working in Kenya, noted that adverse reactions and poor compliance with standard falciparum malaria chemoprophylaxis regimens (including mefloquine, doxycycline, and the combination of chloroquine/proguanil) make it desirable to have better chemoprophylactic options. Newer agents, not yet approved for prophylactic use in many countries, hold promise of improved usefulness.
Azithromycin, a macrolide antibiotic, has been tested during malaria prophylaxis trials in Kenya. It is more than 80% effective when taken daily and about 64% effective with weekly dosing. In Thailand and Indonesia, effectiveness is about 72%. Despite some promise, azithromycin has suboptimal efficacy (especially in nonimmune individuals) and must be taken daily.
The combination of atovaquone and proguanil (with tablets containing 250 mg of atovaquone and 100 mg of proguanil; available commercially largely in Europe and Australia) is approved in some instances as a curative treatment agent. Studies in several African countries suggest that it is also at least 95% effective in prophylaxis using a single pill daily. There appears to be a "causal" prophylactic effect on liver-phase hypnozoites, so prophylactic treatment can be stopped one week after leaving an endemic area.
Tafenoquine (WR238605) is a primaquine analog that destroys all forms of the malaria parasite. G6PD deficiency should be ruled out in any individual planning to use it, but studies in Kenya, Ghana, and Thailand suggest that twice-weekly dosing is more than 90% effective in preventing malaria. With broad action against the different forms of malaria, it can be discontinued as soon as the treated traveler leaves the malaria-endemic area. Similarly, 15-30 mg of daily primaquine are effective in prophylaxis in G6PD-normal individuals, but the dosing is less convenient than with tafenoquine. Due to its influence on cardiac conduction, halofantrine is not a good choice as a prophylactic agent nor are artemesinin derivatives due to their brief duration of activity. Ciprofloxacin is clinically ineffective against malaria.
New Diagnostics—Kevin Kain, The Toronto Hospital, Toronto, ON, Canada.
Toronto’s Kevin Kain then reviewed newer diagnostic tests for malaria. A clinical diagnosis of malaria is accurate in fewer than half of cases. Traditional malaria smear readings in "local" overseas settings were confirmed as accurate in only 25-75% of cases sent to the CDC in one recent study. Thus, there has been considerable interest in developing more accurate diagnostic tests.
One new class of malaria tests uses monoclonal antibodies against proteins released by P. falciparum parasites. Parasight F, ICT, and PATH are such examples, and these tests perform better than standard microscopy, with accuracy rates greater than 95%.
Another test strategy, including that used in the Optimal brand, uses antibody binding to test for parasite LDH. These tests are more than 90% sensitive and specific for P. falciparum and about 83% sensitive and 95% specific for P. vivax. Thus, new tests provide helpful information, but clinicians must realize that inaccurate results are still possible. The Parasight F test, for instance, can produce false-positives in the presence of rheumatoid factor and can also remain positive for up to a month following successful antimalarial treatment.
Malaria Vaccines—Progress and Prospects of Clinical Trials—Blaise Genton, Polyclinique Médicale Universitaire, Lausanne, Switzerland.
Blaise Genton, formerly working in Papua, New Guinea, but now based in Switzerland, reviewed the progress and prospects for a malaria vaccine. Currently, no effective vaccine is available, but testing continues using different forms of vaccines and different adjuvants. For the future, DNA vaccines hold the most promise. To produce these vaccines, a fragment of the parasite gene is incorporated into a plasmid vector. When this material is processed within recipient cells, parasite antigen is produced and stimulates an antibody response. Work is in progress at directing these DNA vaccines toward protection against multiple stages of the parasite’s life cycle. Nonetheless, it is not clear if vaccines will obviate the need for insect precautions and chemoprophylaxis at any time in the foreseeable future.
Which of the following holds the best promise as a potential antimalarial chemoprophylactic agent?
a. Artemesinin derivatives
b. Tafenoquine
c. Halofantrine
d. Ciprofloxacin
e. Azithromycin
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