Temporal and spatial distribution of the variants of merozoite surface protein-1 (MSP-1) in Plasmodium falciparum populations in Brazil

The polymorphic, merozoite surface protein-1 (MSP-1) of Plasmodium falcipar um, an antigen of the parasite's asexual blood-stages, is a major malaria v accine candidate. Nucleotide sequences of each variable domain or block of this antigen may be grouped into one of three possible allelic types (K1, M AD20 and RO33), and 24 major types of the msp-1 gene may be defined, as uni que combinations of allelic types in these variable blocks. Isolates collec ted from the Brazilian Amazon, over a period of 14 years, have now been inv estigated, by PCR-based typing of the msp-1 gene. Thirteen of the 24 possib le gene-types were identified, and 336 P. falciparum clones were fully type d among 239 isolates. Most parasites (87%) belonged to one of the seven mos t frequent gene-types. Marked temporal variation in the distribution of msp -1 variants was found when comparing parasites sampled in the same sites at intervals of at least 5 years. Spatial variations were also found when com paring parasites from both neighbouring and distant sites within the Amazon Basin. The between-population variance in the frequencies of msp-1 allelic types found in Brazil, as estimated by Wright's F-ST statistic, is of simi lar magnitude to that found in previous world-wide comparisons. The potenti al implications of these findings for the development of an MSP-1 based, mu ltivalent malaria vaccine are discussed.