Emergence of simian malaria

In the 90’s, Plasmodium falciparum and P. vivax were the dominant malaria parasites reported in Sabah. Due to the concerted efforts of the government to control malaria, malaria cases due to these species had decreased over the years. However, Plasmodium knowlesi, a simian malaria parasite from the long-tailed macaque monkey has now become the dominant species. Anopheles mosquitoes of the Leucosphyrus group are the bridge vectors between the macaques and humans. Androgenetic actions such as deforestation for agriculture and other changes in land-use have contributed to the high infection of Plasmodium knowlesi especially in areas near the forests and oil palm estates. This has affected the Malaysian national malaria elimination program. We conducted sampling of Anopheles mosquitoes using human landing catch in various sites in Kudat and other areas from 2013-2017, to study the mosquito population changes over time and in different habitat types. Anopheles mosquitoes were dissected as well as tested with PCR for presence of Plasmodium parasites. The incriminated vector, An. balabacensis, demonstrated early biting activity and feeding predominantly outdoors in the early evening between 1800-2000 hrs. This suggests that current vector control tools such as indoor residual spraying and insecticide treated bed-nets may not be as effective as we wish. However computer models suggest that these methods are sufficient to reduce the risk of transmission to humans. Our data shows that An. balabacensis is found more in peridomestic area than inside the house, and more in forested areas and oil palm estates.

Author(s): Tock H. Chua

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