Naturally acquired Plasmodium knowlesi malaria in human, Thailand

Abstract

We describe a case of naturally acquired infection with Plasmodium knowlesi in Thailand. Diagnosis was confirmed by the small subunit ribosomal RNA and the mitochondrial cytochrome b sequences. The occurrence of simian malaria in human has signified the roles of wild primate populations in disease transmission in some malaria-endemic areas.

Figure 1

Giemsa-stained thin blood films depicting A) ring stage, B) tenue form of young trophozoite, C) band-shaped growing trophozoite, D) growing trophozoite with little or no amoeboid activity, E) double growing trophozoites, F) early schizont, G) late schizont in an erythrocyte with fimbriated margins, and H) mature macrogametocyte. Discernible Sinton and Mulligan stippling is in C, D, and F.

Figure 2

Neighbor-joining tree based on the asexually transcribed SSU rRNA sequences displaying the phylogenetic position of isolate A1 in this study in relation to other Plasmodium knowlesi isolates (AY327549-AY327556 from humans, and L07560, U72542, and AY327557 from monkeys) and P. fragile (M61722). The tree was constructed with Kimura's two-parameter distance. including transitions and transversions as implemented in the MEGA version 2.1 software. Bootstrap percentages more than 50% based on 1,000 replicates are shown on the branches.