These strategies have produced striking reductions in the reported number of human malaria cases in Thailand over the past 30 years, although there have been regional differences with respect to the extent of the reduction. Epidemiological evidence of declining numbers of cases suggest that control measures may be able to produce substantial reductions GSK J4 cell line in local parasite effective population sizes of malaria parasite species, which in turn might cause reduction in the level of parasite

polymorphism. Thus, after extensive mobilization of non-vaccine control measures, a local population may have sufficiently reduced polymorphism that a location-specific vaccine might be feasible and effective. We tested the hypothesis that control measures can induce a loss of polymorphism at antigen-encoding loci by examining data on numbers of P. falciparum and P. vivax infections and nucleotide sequence polymorphism at selected antigen-encoding loci in two areas of Thailand. We compared data from

two different regions: (1) Tak Province, in northwestern Thailand, along the border of Myanmar (henceforth NW); and (2) from Yala and Narathiwat Provinces in southern Thailand (henceforth South; Fig. 1). Reported cases of malaria have declined sharply in the South over the mTOR inhibitor past three decades, but less sharply in the NW [19] and [21]. By comparing sequence polymorphism at antigen-encoding loci, we tested the hypothesis that the more severe decline in malaria cases in the South has been accompanied by a reduction in polymorphism at these vaccine-candidate loci. We randomly recruited blood samples from symptomatic malaria patients from northwestern (Tak Province) and southern Thailand (Yala and Narathiwat Provinces) collected during 1996–1997 for P. falciparum samples and 2006–2007 for both P. falciparum and P. vivax samples. The ethical aspects of this study have been approved by the Institutional Review Board of Faculty of Medicine, Chulalongkorn University. DNA was extracted from either venous blood samples using QIAamp kit (Qiagen, Hilden, Germany) or finger-pricked blood spotted onto filter

paper. We excluded multiple clone infections of P. falciparum isolates by genotyping of polymorphic block 2 of the merozoite surface protein-1 Metalloexopeptidase (Pfmsp-1) and the central repeat region of the merozoite surface protein-2 (Pfmsp-2) genes as described by others [22]. Likewise, genotyping of P. vivax isolates was performed using the highly polymorphic block 6 of the merozoite surface protein-1 (Pvmsp1) [23]. Further, samples showing superimposed eletropherogram signals during DNA sequencing were also excluded from analysis. The complete nucleotide sequences of P. falciparum csp and msp-2 and of P. vivax msp-1, ama-1 and msp-4 were obtained by using respective forward and reverse primers for each gene as described previously [10], [12], [19], [23] and [24]. Sequences of P.