Abstract:
Naturally acquired human infections with Plasmodium knowlesi are endemic in Southeast Asia. Our previous survey in 2006-2007 has shown a wide-spread and low prevalence of this simian malaria in Thai patients. This follow-up study in the same endemic areas in 2008-2009 has revealed a stable prevalence of P. knowlesi among malaria patients whereas a significance difference in the prevalence of 4 human malaria species occurred. Retrospective analysis of blood samples from malaria patients collected in 1996 in one of these endemic areas has reaffirmed a stable prevalence of P.knowlesi when compared to those in 2006-2007 and 2008-2009, indicating that this simian malaria is not newly emergent human malaria in Thailand. Importantly, identical merozoite surface protein-1 sequences were observed between isolates from a patient and a pig-tailed macaque living in vicinity, suggesting potential cross-transmission of P.knowlesi from naturally infected macaques to humans.
