A panel of 30 monoclonal antibodies was established against asexual erythrocytic stages of Plasmodium vivax and used to investigate the antigenic composition of the parasite. At least 38 different antigenic polypeptides of P. vivax were characterized by the Western blot technique. The possible location of these antigens, as well as their stage and species specificity, was determined on the basis of the staining patterns produced by these antibodies on air-dried parasites in the indirect immunofluorescence test. Immunofluorescence performed with 30 different monoclonal antibodies on 50 different isolates of P. vivax obtained from patients showed that a high level of antigenic polymorphism prevailed in P. vivax. Only six monoclonal antibodies reacted with epitopes that were represented in more than 80% of parasite isolates, and therefore, appeared to be relatively conserved among different isolates. The other 24 monoclonal antibodies reacted with only 20 to 70% of parasite isolates.

An enzyme-linked immunosorbent assay (ELISA) based on the svnthetic Deutide (NANP)m was used to characterize the sporo;oGe an&bodies 'in an unusual Plasmodium falciparum outbreak in a non-malarious area in Sri Lanka. A positive antibody response was seen in 62% of patients with their first P. falciparum illness. There was no correlation between sporozoite antibodies and the antibody against blood stages, determined by immunofluorescence assay. The majority (91%) of the patients lost the antibodies to circumsporozoite (CS) protein within one year (in the absence of re-exposure). Three patients had high levels of CS antibodies even after one year, and this persistence was related to the level of the initial antibody response. In the area of the outbreak 10% of schoolchildren had antibodies to the (NANP)a peptide. 21% of the 42 children with present or past overt malaria were antibody positive. Of the children with no such background, 8% were antibody positive. The corresponding seropositivity rates for asexual blood stages were 31% and 1% for the 2 groups respectively. It is concluded that (NANP)@ ELISA is potentially a valuable tool in sero-epidemiology, particularly in situations of seasonal transmission and recurrences due to drug resistance.