Monkey malaria

Monkey malaria is caused by a malaria parasite, the Plasmodium knowlesi. The parasite is endemic in Southeast Asia and causes primarily malaria in long-tailed macaques (Macaca fascicularis) and pig-tailed macaques (Macaca nemestrina), but increasingly infects humans. It is largely the result of continued massive deforestation, mostly for palm oil plantations.

Plasmodium knowlesi is one of the six species of malaria parasite that infect humans, the others being: Plasmodium vivax, Plasmodium malariae, Plasmodium falciparum, Plasmodium ovale curtisi and Plasmodium ovale wallikeri. Plasmidium ovale has recently been shown to consist of two subspecies[1]. Plasmodium knowlesi appears to occur in regions that are reportedly free of the other types of human malaria.

Monkey malaria is an emerging infection that was reported for the first time in humans in 1965[2]. These days it accounts for up to 70% of malaria cases in certain areas in Southeast Asia, particularly in Borneo, Cambodia, Malaysia, Myanmar, Philippines, Singapore, Thailand and neighboring areas.

The parasite is transmitted by the bite of several species Anopheles mosquitoes. These Mosquitoes are typically found in forested areas in Southeast Asia, but it is entirely possible that the mosquito might be able to adapt to environments with less trees.

The Plasmodium knowlesi parasite replicates and completes its blood stage cycle in 24-hour cycles[3]. This results in fairly high loads of parasite densities in a very short period of time. This makes it a potentially very severe disease if it remains untreated. The associated fever also occurs at 24-hour cycles. This is called a quotidian fever.

[1] Sutherland et al: Two nonrecombining sympatric forms of the human malaria parasite Plasmodium ovale occur globally in Journal of Infectious Diseases – 2010
[2] Chin et al: A naturally acquired quotidian-type malaria in man transferable to monkeys in Science – 1965
[3] Cox-Singh et al: Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening in Clinical Infectious Diseases – 2008