Seroepidemiology of malaria in northern Thailand.

The seroepidemiology of malaria in two areas of Northern Thailand was studied by means of the indirect immunofluorescent antibody tests (IFAT). In one transmission has been interrupted completely for over 30 years, but in the other area transmission still occurs at a low level. Results of the survey for antibodies confirm existing parasitological findings and reflect both the recent and past history of malaria in both areas. The IFAT is less sensitive to recent malaria infection in very young people in an area of low endemicity than is the number of reported slide proven cases, but as age and cumulative exposure increase the IFAT reflects period prevalence in adults of ages 20--40. Thus, the serological data are complementary to other available information. This study also confirms the observation that malaria antibodies may last for over 30 years in people who formerly lived in hyperendemic areas and had multiple infections with the malaria parasite.