Abstract. The genetic characteristics of Plasmodium falciparum isolates collected in French Guiana, where malaria transmission is low and occurs in isolated foci, were studied. Blood samples were collected from 142 patients with symptomatic malaria and typed using a polymerase chain reaction-based strategy for merozoite surface protein-1 (MSP-1) block 2, the MSP-2 central domain, and glutamate-rich protein (GLURP) repeat domain polymorphism. This showed that the parasite population circulating in French Guiana presented a limited number of allelic forms (4, 2, and 3 for MSP-1 block 2, MSP-1, and GLURP, respectively) and a small number of mixed infections, contrasting with the large genetic diversity of parasite populations and infection complexity reported for Africa, Asia, and other parts of South America. Two groups of isolates displaying identical 3 loci allele combinations were further studied for the Pf332 antigen, histidine-rich protein-1, thrombospondin-related anonymous protein, and Pf60 multigene family polymorphism. Within each group, most isolates were identical for all markers tested. This suggests a high rate of self-fertilization of P. falciparum parasites in French Guiana, resulting in homogenization of the population. The implications of these findings for malaria control in areas of low endemicity are discussed.Malaria parasites show extensive genetic diversity for a number of markers, including enzymes, antigens, and drug resistance.

Abstract. Variant-and strain-specific immunity to malaria in Saimiri monkeys infected with homologous O and R variants of the Palo Alto strain (FUPSP) of Plasmodium falciparum or by various heterologous divergent strains were studied. Following homologous reinfections, the primary immune response in monkeys was effective only against the same variant type but not against the other variant, which differed only by antigens exposed at the surface of the infected red blood cell. In contrast, after two successive inoculations with a single variant type, a variant transcending immunity developed to both O and R parasite populations. The immunity against FUPSP in monkeys repeatedly infected with various combinations of heterologous strains, including Sal I, Tanzania, Camp, FUPCP, FCH4, FVO, and FUPCDC parasites was less effective, resulting at best in protecting the monkey against fulminating infection. However, in several cases, previous or concomitant heterologous infections modified the course of virulent infection by FUPSP parasites, indicating a significant degree of cross-protection between the strains. Therefore, in this model, while variant-and strain-specific antigens are important components of acquired immunity to malaria, the monkey immune response to infection transcends phenotypic antigenic variation and strain diversity.Immunity to malaria in humans is poorly protective and only acquired slowly after several years of exposure to intense transmission. It is a nonsterile immunity and requires frequent boosting if it is to last. 1 Malaria parasites exhibit an extensive antigenic polymorphism as a result of two major factors, allelic diversity and antigenic variation. While antigenic diversity and host adaptation to it are likely to be important parameters to naturally acquired immunity to malaria, little is known about the relationship between antigenic diversity and the protective immune response against infection. 2 It has been suggested that the various allelic forms of genes interfere with and hinder the development of an efficient immune response such that protection is only achieved after exposure to a large number of antigenically distinct parasite strains. 3,4 However, epidemiologic studies are not conclusive on this issue because of the complexity of natural parasite populations, host genetic diversity, and the possible presence of other immune evasion mechanisms such as antigenic variation. [5][6][7][8] It is important to determine the effect of phenotypic variation and antigenic diversity on the development of immunity. This question should be easier to address in experimental models in which the infection is well characterized and controlled. By using different approaches (parasitologic, immunologic, and molecular), we studied the relative importance of conserved and polymorphic antigenic determinants in inducing an effective immunity against Plasmodium falciparum in a monkey model. In this communication, we report the pattern of infections of Saimiri monkeys successively injected with various c...

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