High prevalence of antibodies against circumsporozoite antigen of Plasmodium falciparum without development of symptomatic malaria in travelers returning from sub-Saharan Africa.

Circumsporozoite (CS) antibodies, indicating that falciparum malaria infection has occurred, have been shown to be reliable indicators of transmission in malaria-endemic areas. In order to estimate the actual rate of malaria infection, the prevalence of CS antibodies in serum was investigated by ELISA in a selected population of travelers returning from sub-Saharan Africa without any clinical sign of malaria. Sera from 39 (48.8%) of 80 individual travelers were positive, while this was only true for 8 (5.6%) of 142 travelers who took package tours. The risk of malaria infection was therefore 8.7 times greater for individual tourists than for package-tour travelers. These data demonstrate the importance of adequate malaria chemoprophylaxis in nonimmune travelers to areas with highly endemic disease.