Seroconversion to circumsporozoite antigen of Plasmodium falciparum demonstrates a high risk of malaria transmission in travelers to East Africa.

Circumsporozoite (CS) antibodies have been shown to be reliable indicators of malaria transmission in endemic areas. Their prevalence in travelers can indicate the degree of exposure to plasmodial infection. Two hundred sixty-two short-term travelers to Kenya were recruited to a prospective study to determine the incidence of CS antibody conversion. All travelers were receiving malaria chemoprophylaxis. Serum samples were drawn before departure and 4-6 weeks after their return to Germany. Sera from 310 volunteers who did not leave Germany served as controls. Serum specimens from 13 (4.96%) of the 262 travelers were found to be positive after return. None of the travelers developed symptoms of clinical malaria or antibodies against the blood stages of Plasmodium falciparum. All 310 control samples tested negative. These data demonstrate a considerable risk of malaria transmission for short-term travelers to East Africa.