WASHINGTON — Malaria rates among troops are 44 times greater for those born in seven western African countries than for those born in the United States, a study published in the September issue of Emerging Infectious Diseases found.

The study also suggested these troops were acquiring malaria infection when they were on personal travel to their birth countries in western Africa, rather than on active duty.

Study author Army Col. Mark Fakuda, MD, malaria surveillance program director for the Armed Forces Health Surveillance Center, told U.S. Medicine that the findings are “not surprising.” CDC research also has found that that the highest risk factor for malaria importation in the general U.S. population is in a group called “visiting friends and relatives (VFRs),” he said.

The researchers at the Armed Forces Health Surveillance Center used routine surveillance data from 2002 to 2010 to estimate the rates of malaria in association with the birth countries of active-duty troops in the U. S. military.

During 2002-2010, a total of 835 malaria cases were reported among active military members. Compared with the overall composition of the U.S. military, the proportions of military members with malaria were overrepresented by men (95%) and those 18–34 years of age (87%).

Among military members affected by malaria during the study period, 624 were born in the United States, 107 were born in malaria-endemic countries other than Mexico, and 33 were born in countries where malaria is not endemic or in Mexico. The birth countries of the other 71 were not documented in available records.

When it came to the western African countries, there were 24 cases of malaria in troops from Nigeria and 21 cases from Ghana. The highest malaria rates were among those born in Côte d’Ivoire (54.4/10,000 person-years), Togo (39.5/10,000 person-years), Cameroon (37.6/10,000 person-years) and Ghana (36.0/10,000 person-years). Overall, the malaria rate was 44 higher among troops born in one of the seven western Africa countries (30.5/10,000 person-years) than among those born in the United States (0.70/10,000 person-years).

The study stated that, among the 69 malaria-infected troops who were born in western Africa, the location of malaria acquisition was unknown for 27 (39%). However, “because these persons had no records of military assignments in or deployments to malaria-endemic areas, their infections were probably acquired during personal travel. If so, as many as 62 (90%) of these infections may have been acquired during visits to birth countries,” the authors wrote.

The study suggested that because those who grow up in a malaria endemic area develop partial immunity to malaria parasites. Because of that, they may not be accustomed to or feel the need for chemoprophylactic drugs. After leaving their countries of origin, their acquired immunity wanes, however.

“So there is a perception that immunity will stay with them when they leave a malaria endemic area and then go back home after living outside, perhaps in the Western world or where malaria is not endemic,” said Fakuda. “That immunity wanes and it is a high-risk group, for not only the acquisition of malaria, but some of the severe sequelae thereof.”

The study pointed out that, before deploying to malaria-endemic areas, compliance with the malaria countermeasures is mandatory, and their use is ensured by military supervisors. In contrast, before personal travel to these areas, “counseling regarding malaria prevention may not be readily available or routinely accessed, and use of countermeasures is not enforced,” so that educational measures are needed.

“At the end of the day, there is no nanny,” he said. “The military can’t enforce compliance when folks are on leave. There has to be a direct marketing and education to the soldier or DoD personnel directly.”

The study authors noted limitations to the study. For example, malaria cases were identified from diagnoses reported on administrative records of hospitalizations in U.S. military and civilian medical facilities and from reports of notifiable medical events. Records of hospitalizations in deployed medical facilities, on the other hand, were not available.

In addition, for 71 of the 835 military members with malaria, birthplaces could not be determined from records maintained for health-surveillance purposes.

Wertheimer E, et al “High rates of malaria among U.S. military members born in malaria-endemic countries, 2002-2010” Emerg Infect Dis 2011; 17(9).

CDC Emerging Infectious Diseases

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