Application in clinical epidemiology of new advances in immunology and molecular biology of malaria.

The first purpose was to study the sensitivity of a spot hybridization assay for P. falciparum with a DNA probe. This assay was compared with light microscopy for the detection of low-grade parasitemia. The second purpose was to study in clinically immune individuals the seroreactivity, against a newly identified P. falciparum antigen, deposited in the erythrocyte membrane during merozoite invasion (Perlmann et al., 1984). This antigen is considered to be a potential component in a future vaccine against the blood stage of the parasite. In a holoendemic village in Yekepa area, Northern Liberia, 28 adult men with a high degree of protective immunity against malaria, were shown to have repeatedly low-grade parasitemias of varying density. The spot hybridization assay with the DNA probe was highly sensitive in detecting parasitic infection. The sensitivity was comparable to that of the examination of a blood film for about 15 min by an experienced microscopist. The seroreactivity against Pf 155 antigen varied between a high positive titer to negativity in different subjects, but the reactivity was constant over a period of 15 months for each subject despite numerous new infections and comparable protective immunity against malaria infection.