Indirect fluorescent and haemagglutinating antibodies to malaria in Nigerian students resident in Washington D.C., U.S.A.

Fluorescent and haemagglutinating antibody tests were performed on sera collected from fifty-two adult African students from a holoendemic region of malaria in Nigeria. Period of continuous residence in the U.S.A. among members of the group varied from 2 days to nearly 10 years. None has been diagnosed as having malaria since resident in the U.S.A. and none had taken any form of anti-malaria drug prophylaxis since departure from Nigeria. Both tests indicated that all the students had probably had a past infection with falciparium malaria. All gave a positive reaction to fluorescent antibody (FA) test and in 70% indirect haemagglutination (IHA) titres of 1:16 and above were demonstrated. Twenty-three per cent had FA titres of 1:4096. The malarial antibody titre levels decreased with increase in the interval since last exposure. Generally, the IHA titres were lower than the FA. No malaria parasite was seen in the blood of the students on the one occasion they were examined. The high titre values recorded in those who have been away from the endemic region for over three years suggests that falciparum parasites may persist in the body longer than the usually accepted limit of 3 years.