Meeting Update: Annual Meeting of the American Society of Tropical Medicine and Hygiene (ASTMH) 2008

By Lin H. Chen, MD

Dr. Chen is Assistant Clinical Professor, Harvard Medical School Director, Travel Medicine Center, Mt. Auburn Hospital, Cambridge, MA.

Dr. Chen reports no financial relationships relevant to this field of study.

At the 57th Annual Meeting of the American Society of Tropical Medicine and Hygiene in New Orleans, Louisiana, held from December 7-11, 2008, the Centers for Disease Control and Prevention presented malaria and travel vaccine updates. Dr. Paul Arguin from the Domestic Malaria Unit presented "Malaria Update: Surveillance, Prevention, Treatment." In 2007, 1505 cases of malaria were reported to the National Malaria Surveillance System, including 1 death. The most common species identified was Plasmodium falciparum (43.4%), followed by P. vivax (20.3%). The species in 30% of cases was unknown. Among the patients for whom information was available, 47% were U.S. civilians, 17% were foreign civilians, 2% were military, and 34% were of unknown status. Heading the list of countries where infection occurred were Nigeria (20.3%), India (13.1%), Ghana (10.4%), Tanzania (4.2%), Liberia (4%), and Uganda (3.3%). Among the foreign residents, 19.7% were from India.

Among the U.S. residents, the main countries that were associated with malaria acquisition were Nigeria (24.7%), Ghana (11.6%), India (11.2%), Uganda (4.0%), Honduras (3.6%), and Haiti (3.8%). Estimated relative risk showed West and Central Africa and Oceania to be the regions of highest risk, whereas Central and South Central Asia were the regions of lowest risk. The most common reasons for travel were, once again, visiting friends and relatives (VFR) at about 50%, followed by tourism for about 10% of travelers.

Of interest, one U.S. traveler from New York was documented with P. knowlesi acquired in 2008 in Palawan in the Philippines, with species identification confirmed by PCR at the CDC. P. knowlesi is a simian malaria species that naturally infects macaques in Southeast Asia. It became recognized as a human pathogen in a number of reports.1-5 On microscopy, it resembles human species. P. knowlesi has a 24-hour replication cycle and can cause severe and fatal infections. Large numbers of human cases were reported initially from Malaysian Borneo. Subsequently, human cases were reported from Peninsular Malaysia, Singapore, and the Philippines. One case previously was reported in a Finnish traveler.6

Treatment updates highlighted the artemisinins. Artemether-lumefantrine gained recommendation for approval by the FDA advisory panel on December 3, 2008. In addition to atovaquone-proguanil, artemether-lumefantrine may become the second drug approved for treatment of malaria for travelers going to areas where reliable supplies of the drug may not be available. A second artemisinin drug, artesunate, has become available through WRAIR via the CDC malaria hotline in the past 2 years. Criteria for the release of artesunate are: the patient has malaria; parenteral treatment is required; artesunate is preferred (quinidine not available, has failed, the patient is intolerant, or the drug is contraindicated). Thus far, 37 patients have been treated in the United States through this protocol. Mean age was 35 years, 60% were male; 90% P. falciparum malaria, 7% P. vivax malaria; 84% had exposure in Africa, 10% in Asia, 6% in the Americas. Measures of delays in treatment showed the time from request of drug to shipping was 2.7 hours, and the time to arrival was 2.9 hours. Time from request to treatment was approximately 7.2 hours.

Prevention emphasized individual risk assessment based on destination country (transmission intensity, focal areas with transmission even when, within a country, the overall risk is low), type of traveler (especially VFRs), accommodations, etc. Major upcoming changes are: new country-specific guidance table that is separate from yellow fever; malaria risk categories updated to include five groups (limited malaria, P. vivax-predominant, chloroquine-sensitive, chloroquine-resistant, and mefloquine-resistant areas); and inclusion of primaquine as a first-line drug. The updated recommendations emphasize personal protective measures for areas considered as having limited malaria. For areas with mainly P. vivax, use primaquine as the first-line preventive agent.

Nina Marano, DVM, MPH, Dipl ACVPM, from the Division of Quarantine and Global Migration, presented "Travelers' Vaccine Update from the CDC." She reviewed the prevention of rabies, Japanese encephalitis, yellow fever (YF), and gave a preview of the 2010 Yellow Book.

The CDC initiated a country-specific rabies risk assessment based on rabies endemicity in the country, availability of biological agents, and travelers' expected risk of exposure. Rabies risk assessment is used to guide pre-exposure prophylaxis recommendations for travelers. Special risk among children is noted, and mapping of the risk areas by category of risk is planned. Emphasis is placed on dog avoidance and prevention of bites and scratches. A short supply of rabies vaccines in the United States occurred in 2008 due to renovation of a manufacturing plant, and restrictions on rabies vaccines applied to pre-exposure prophylaxis that affected travel clinics in particular. Since October 2008, the supply for post-exposure vaccines has stabilized.

As many travel medicine practitioners know, the only FDA-approved Japanese encephalitis vaccine is JE-Vax, whose manufacture was discontinued around 2005, and allocations took place in 2008. The restriction limits 9 doses of the vaccine per month to previous customers only. A new, inactivated, cell-culture derived JE vaccine has been undergoing FDA review and likely will receive approval very soon. For travelers at risk (spending 1 month in endemic areas or short-term travel with itineraries that may pose increased risk, such as significant rural exposure or outdoor activities), provide advice regarding insect bite precautions and refer to providers or clinics that previously have ordered JE-Vax from Sanofi-Pasteur.

A recent publication updates yellow fever vaccine risks (Lindsey, et al. Adverse event reports following yellow fever vaccination. Vaccine 2008;26:6077-82). The revised estimates are based on 660 adverse events reported to VAERS from 2000 to 2006. The denominator is obtained from the number of doses purchased for civilians, or 200,000 doses per year. A survey of 3400 U.S. providers in 2006 obtained the age and sex of vaccine recipients. Ninety-five percent of the AEs were associated with primary vaccines, and 61% were women. Median time to occurrence was 1 day, with a range 0-50 days. There were 72 serious adverse events (SAE), including 12 neurotropic disease (YF-AND), 6 viscerotropic disease (YF-AVD), and 4 deaths. SAE rates are calculated. (See Table, below.) A new ACIP work group for YF vaccine plans to update the recommendations.

A World Health Organization YF risk mapping work group is planning to update the risk map and harmonize CDC and WHO recommendations. The work group will focus on countries that are non-holoendemic, and define areas within countries as endemic, transitional, or low risk. YF vaccine will be recommended for travel to areas that are endemic or transitional. The decision to vaccinate for travel to areas that are low risk will be based on itinerary, extent of exposure, and risk factors. Updated YF vaccine recommendations include: risk areas are updated for Brazil, Paraguay, and Argentina; vaccine is not needed for travel to Tobago; and vaccine is needed only for certain areas of Chad, Mali, Mauritania, Niger, and Sudan.

Health Information for International Travel, the CDC Yellow Book, 2010 will be available in May 2009. The editorial team includes Amanda Whatley, Gary Brunette, Phyllis Kozarsky, Alan Magill, and David Shlim. It will be in a larger size, with bulleted presentation and new tables to be easy to use in clinical settings. New items include pre-travel consultation, perspectives, and health considerations for newly arrived immigrants and refugees. A new chapter will highlight selected destinations and itineraries. Finally, new sections will focus on medical tourism, mental health, drug interactions, respiratory infections, as well as special groups (air crews, long-term travelers, and expatriates), and additional diseases. The changes promise to enrich an already valuable resource for travel medicine practitioners.

Acknowledgment: The author thanks Drs. Paul Arguin and Nina Marano for sharing their presentations and for reviewing the summary.

References

  1. Singh B, Kim Sung L, Matusop A, et al. A large focus of naturally acquired Plasmodium knowlesi infections in human beings. Lancet 2004;363(9414):1017-1024.
  2. Jongwutiwes S, Putaporntip C, Iwasaki T, et al. Naturally acquired Plasmodium knowlesi malaria in human, Thailand. Emerg Infect Dis. 2004;10(12):2211-2213.
  3. Luchavez J, Espino F, Curameng P, et al. Human infections with Plasmodium knowlesi, the Philippines. Emerg Infect Dis. 2008;14(5):811-3.
  4. Ng OT, Ooi EE, Lee CC, et al. Naturally acquired human Plasmodium knowlesi infection, Singapore. Emerg Infect Dis. 2008;14(5):814-6.
  5. Vythilingam I, Noorazian YM, Huat TC, et al. Plasmodium knowlesi in humans, macaques and mosquitoes in peninsular Malaysia. Parasit Vectors. 2008;1(1):26.
  6. Kantele A, Marti H, Felger I, et al. Monkey malaria in a European traveler returning from Malaysia. Emerg Infect Dis. 2008;14(9):1434-6.