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Late-Onset Malaria, Despite Chemoprophylaxis

Chemoprophylaxis doesn't guarantee protection against malaria

Many malaria chemoprophylactic agents affect only the parasite's blood stage and therefore do not protect against relapses due to Plasmodium vivax or P. ovale. Investigators recently examined malaria surveillance data from the U.S. and Israel during the 1990s to determine the frequency and timing of late-onset (>2 months after return) malaria in travelers. They included only cases (300 from Israel, 2822 from the U.S.) in which a single species was identified as the cause.

With P. falciparum malaria, symptoms began 2 months after return in >95% of cases; with P. vivax or P. ovale malaria, symptoms began >2 months after return in 64%. Approximately two thirds of patients reported taking antimalarials active against the parasite's blood stages. Overall, nearly 25% of all cases of malaria were late-onset infections in persons who had taken recommended drugs.

Comment: Clinicians should be alert to late-onset malaria in travelers, even those who have taken chemoprophylaxis. This study underscores the deficiencies in antimalarial regimens. Chloroquine, mefloquine, and doxycycline, which suppress the parasite's blood stage, were the agents generally used during the study period. Since then, the atovaquone-proguanil combination (Malarone), which acts against both blood and liver stages, has become available, but data on its efficacy against P. vivax malaria are still limited. Primaquine, which acts against the liver stage and is employed for radical cure of P. vivax and P. ovale infections, is also effective in preventing malaria. However, blood testing for G6PD deficiency is necessary before considering its use. The editorialists note the vast differences between travelers and residents of endemic areas in burden of malaria and preventive approaches.

— Mary E. Wilson, MD

Published in Journal Watch Infectious Diseases November 7, 2003

Citation(s):

Schwartz E et al. Delayed onset of malaria -- Implications for chemoprophylaxis in travelers. N Engl J Med 2003 Oct 16; 349:1510-6.

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• Medline abstract (Free)

Wellems TE and Miller LH. Two worlds of malaria. N Engl J Med 2003 Oct 16; 349:1496-8.

• Original article (Subscription may be required)
• Medline abstract (Free)