Bionomics of Anopheles latens in Kapit, Sarawak, Malaysian Borneo in relation to the transmission of zoonotic simian malaria parasite Plasmodium knowlesi

Abstract

Background: A large focus of human infections with Plasmodium knowlesi, a simian parasite naturally found in long-tailed and pig-tailed macaques was discovered in the Kapit Division of Sarawak, Malaysian Borneo. A study was initiated to identify the vectors of malaria, to elucidate where transmission is taking place and to understand the bionomics of the vectors in Kapit.

Imported Plasmodium knowlesi Malaria in a French Tourist Returning from Thailand

“…Usually human P. knowlesi infections occur during stays in forest areas 3,5,9,12,13,16 as the four vector species suspected to be responsible for the transmission of P. knowlesi ( Anopheles hackeri , Anopheles balabacensis , Anopheles cracens , Anopheles latens ), are rather arboreal species. [21][22][23] Indeed, these anopheles from the Leucosphyrus group, are found preferentially in the canopy of the rain forest as is the natural monkey host. In this case, as in that described from the Philippines, 15 the subjects stayed on the seaside right next to the forest fringe and the malaria transmissions most likely happened directly on the beach.…”

Human Infections and Detection of Plasmodium knowlesi

“…Human-to-human, monkey-to-human, and human-to-monkey transmission of P. knowlesi was demonstrated by using A. balabacensis, with incubation periods in the vector of 12 to 13 days. In Kapit, Malaysian Borneo, where most of the human knowlesi malaria cases have been described, A. latens has been incriminated as the vector (82,83). This mosquito species feeds mainly between 7 and 10 p.m. in the forest, is attracted to both long-tailed macaques and humans, and prefers to feed on macaques at higher elevations.…”

“…This species is highly zoophilic and was previously found to feed on macaques at the canopy level and on humans at the ground level. None of these vectors of P. knowlesi were found to be infected with the human malaria parasites P. falciparum, P. vivax, P. malariae, and P. ovale during recent entomological surveys in Sarawak (82,83) and Peninsular Malaysia (44). Interestingly, at 4 collection sites in the forest and forest fringe areas near a village in south central Vietnam, A. dirus mosquitoes were found to harbor sporozoites of P. knowlesi alone and mixed with P. vivax or P. falciparum and also mixed with both P. falciparum and P. vivax (62,85).…”

Natural Plasmodium knowlesi malaria infections in humans

“…La búsqueda de huéspedes y vectores para determinar el potencial zoonótico de esta infección, se inició en Malasia (34,36). Anopheles hackeri se identificó como el vector más importante de P. knowlesi (37), A. balabacencis introlatus, como el vector de P. cynomolgi (38), y A. leucosphyrus como el de P. inui (39), plasmodios causantes de malaria en simios.…”

“…Posteriormente, se determinó que A. leucosphyrus actúa como vector de P. knowlesi, alimentándose tanto de humanos como de simios, y que la mayor tasa de picaduras ocurre en la periferia de la selva (6,74 %) y es menor en la selva (1,85%) o dentro de las viviendas (0,28 %) (34), lo que permite suponer que los humanos adquieren la infección cuando se movilizan para trabajar en la selva (36). Se piensa que la restricción del grupo leucosphyrus al hábitat selvático, la falta de oportunidades para infectar a humanos y la competencia evolutiva entre las distintas especies de plasmodios, son condiciones que han limitado las infecciones de P. knowlesi en la población humana (41).…”