Abstract
The simian malaria parasite Plasmodium knowlesi is transmitted in the forests of Southeast Asia. Symptomatic zoonotic knowlesi malaria in humans is widespread in the region and is associated with a history of spending time in the jungle. However, there are many settings where knowlesi transmission to humans would be expected but is not found. A recent report on the Ra-glai population of southern central Vietnam is taken as an example to help explain why this may be so.
Highlights
A recent study on Plasmodium knowlesi malaria in Vietnam failed to discover symptomatic P. knowlesi in the human population [1]
To screen properly this important population in Vietnam for P. knowlesi infection, PCR negative samples found during the primary screen, those that were not amplified by falciparum, vivax, malariae or ovale specific PCR primers, would have been more likely to yield positive results for P. knowlesi
Of the three P. knowlesi positives reported, one was negative by microscopy and the others were either P. vivax or P. vivax with P. falciparum by microscopy
Summary
A recent study on Plasmodium knowlesi malaria in Vietnam failed to discover symptomatic P. knowlesi in the human population [1]. The population screened was mainly of Ra-glai ethnicity, living in hilly, densely forested areas with frequent overnight stays in the jungle. There are many parallels with the population in Sarawak Malaysian Borneo, where a large number of human cases of zoonotic knowlesi malaria occur annually [2,3]. The authors report that vectors of P. knowlesi are in the area, but it is not known if there are macaques or if they carry P. knowlesi parasites [4]. All of the indicators suggest that human cases of P. knowlesi could occur in this population, which is, worthy of screening
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