TESTING FOR ANTI-CIRCUMSPOROZOITE AND ANTI-BLOOD-STAGE ANTIBODIES FOREPIDEMIOLOGIC ASSESSMENT OF PLASMODIUM-FALCIPARUM INFECTION IN TRAVELERS

The purpose of this investigation was to assess the role of serology f or establishing incidences of Plasmodium falciparum malaria and of exp osure to P. falciparum in epidemiologic studies of travelers using che moprophylaxis. The design was a prospective cohort study involving 548 short-term Dutch travelers to areas endemic for P. falciparum malaria , Sera were collected before departure and, together with the medical history, 2-6 weeks after return. All sera were tested for anti-circums porozoite (CS) antibodies by an R32tet(32)-ELISA; sera of subjects rep orting febrile illness during travel or after return or with anti-CS r esponses were tested for anti-blood-stage antibodies by an indirect fl uorescence antibody test (IFAT), Five subjects (0.9%) reported P. falc iparum malaria confirmed by thick blood smear examination (documented cases) and six (1.0%) reported treatment for malaria without a documen ted diagnosis (presumptive cases), Conversions in the IFAT were detect ed in six subjects, including all five documented cases and one presum ptive case, Anti-CS antibodies were detected in seven subjects (1.3%), including three documented cases and four of 442 subjects with no his tory of fever or malaria treatment (0.9%). Incidence rates per 1,000 p erson-months of travel (95% confidence interval) of infection with P. falciparum, whether or not suppressed by chemoprophylaxis, were 16.9 ( 8-31) for all destinations and 91.6 (33-200) for West Africa. In epide miologic studies of P. falciparum malaria in travelers, testing for an tibodies to blood stages can increase the sensitivity and specificity of case detection; testing for antibodies to sporozoites may be useful for the assessment of exposure to P. falciparum in travelers using ch emoprophylaxis, but the sensitivity is limited.