Abstract
Plasmodium knowlesi, a simian malaria parasite, has been in the limelight since a large focus of human P. knowlesi infection was reported from Sarawak (Malaysian Borneo) in 2004. Although this infection is transmitted across Southeast Asia, the largest number of cases has been reported from Malaysia. The increasing number of knowlesi malaria cases has been attributed to the use of molecular tools for detection, but environmental changes including deforestation likely play a major role by increasing human exposure to vector mosquitoes, which coexist with the macaque host. In addition, with the reduction in human malaria transmission in Southeast Asia, it is possible that human populations are at a greater risk of P. knowlesi infection due to diminishing cross-species immunity. Furthermore, the possibility of increasing exposure of humans to other simian Plasmodium parasites such as Plasmodium cynomolgi and Plasmodium inui should not be ignored. We here review the current status of these parasites in humans, macaques, and mosquitoes to support necessary reorientation of malaria control and elimination in the affected areas.
Highlights
For many years, it has been accepted that only 4 species of Plasmodium namely Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale cause natural malaria infection in humans
Since the focus of the review article is on Southeast Asia, other simian Plasmodium species infecting humans in other parts of the world are not discussed in detail
As P. inui and P. cynomolgi are the most prevalent simian malaria parasites in the macaque hosts and vectors in Southeast Asia, humans are exposed to these parasites by bites of infectious mosquitoes [66]
Summary
It has been accepted that only 4 species of Plasmodium namely Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale cause natural malaria infection in humans. It was postulated that human infection with simian malaria parasites is a rare event [5] This scenario was greatly challenged when a large focus of human P. knowlesi infection was reported among the local population in Sarawak, Malaysia in 2004 [6]. Plasmodium knowlesi: What’s believed that P. knowlesi infections in humans had been there much earlier but were only detected when molecular tools were adopted [7] Under experimental conditions, both P. inui [8] and P. cynomolgi [9,10] can infect humans through mosquito bites, while natural P. cynomolgi infection had been reported recently [11,12,13,14,15]. We here review the current occurrence of P. knowlesi in human, mosquito, and macaque hosts, examining the possible emergence of other simian Plasmodium species as zoonoses in Southeast Asia
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