Abstract
Population genetic analysis revealed that Plasmodium knowlesi infections in Malaysian Borneo are caused by 2 divergent parasites associated with long-tailed (cluster 1) and pig-tailed (cluster 2) macaques. Because the transmission ecology is likely to differ for each macaque species, we developed a simple genotyping PCR to efficiently distinguish between and survey the 2 parasite subpopulations. This assay confirmed differences in the relative proportions in areas of Kapit division of Sarawak state, consistent with multilocus microsatellite analyses. Analyses of 1,204 human infections at Kapit Hospital showed that cluster 1 caused approximately two thirds of cases with no significant temporal changes from 2000 to 2018. We observed an apparent increase in overall numbers in the most recent 2 years studied, driven mainly by increased cluster 1 parasite infections. Continued monitoring of the frequency of different parasite subpopulations and correlation with environmental alterations are necessary to determine whether the epidemiology will change substantially.
Highlights
Population genetic analysis revealed that Plasmodium knowlesi infections in Malaysian Borneo are caused by 2 divergent parasites associated with long-tailed and pig-tailed macaques
P. knowlesi malaria has been described across Southeast Asia, but most clinical cases are still reported in Malaysian Borneo [3,5,6,7,8]
To determine the frequency of the 2 P. knowlesi subpopulations over time, we investigated samples derived from Kapit division, Sarawak state, Malaysian Borneo, where high incidence of cases has been reported [7]
Summary
Population genetic analysis revealed that Plasmodium knowlesi infections in Malaysian Borneo are caused by 2 divergent parasites associated with long-tailed (cluster 1) and pig-tailed (cluster 2) macaques. Population genetic surveys of P. knowlesi infections in humans across Malaysia have revealed 2 divergent subpopulations of the parasite in Malaysian Borneo that are associated with the 2 macaque species locally, suggesting 2 independent zoonoses [12,13]. Limited WGS [14,15] and microsatellite [13] genotyping of P. knowlesi isolates derived from human and only long-tailed macaque hosts from peninsular Malaysia showed allopatric divergence for this subpopulation cluster from those of Malaysian Borneo because of geographic separation by the South China Sea. Increasing numbers of P. knowlesi malaria cases detected might be due to increased zoonotic exposure along with a reduction of endemic malaria parasite species [16].
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