Serological investigations in retrospective diagnosis of malaria.

Sera were obtained in 415 known cases of malaria (88 residents, 327 immigrants) at different times after diagnosis. Three antigens were used in the indirect fluorscence antibody test to detect antibodies to either Plasmodium falciparum or P vivax. Results in residents and immigrants were analysed separately. Most residents had detectable antibodies within one week after an attack, which began to wane after a month. The strongest reactions were obtained in cases of falciparum malaria with the homologous antigen and in cases of vivax malaria with P fieldi. The overall pattern of results was the same in the immigrants but the proportions positive for malaria antibodies, mean titres, persistence of antibodies, and the cross-reaction were usually greater. Testing for malaria antibodies is probably of value in the retrospective differential diagnosis of malaria in patients who have not been exposed to malaria before but must be interpreted with caution in others.