8% ( Daneshvar et al., 2009). In a recent post-mortem analysis of a patient who died of P. knowlesi, some evidence for parasite sequestration CHIR-99021 chemical structure in the brain, as described for P. falciparum, was found ( Cox-Singh et al., 2010). In vivo, P. knowlesi responds to chloroquine ( Daneshvar et al., 2010). In a prospective evaluation of oral chloroquine and primaquine therapy in patients admitted in Sarawak, with PCR-confirmed single P. knowlesi infection, oral chloroquine was given for three days followed by, at 24 h, oral primaquine for two consecutive days. Of 73 patients recruited, 60 completed follow-up over 28 days. The median fever

clearance time was 26.5 h (inter-quartile range: 16–34). The mean parasite clearance time to 50% (PCT50) and 90% (PCT90) were 3.1 h (95%

confidence interval (CI): 2.8–3.4) and 10.3 h (95% CI: 9.4–11.4), respectively. These clearance times were more rapid than in a comparison group of 23 patients with vivax malaria. No P. knowlesi recrudescences or re-infections were detected by PCR. Therefore, in Sarawak chloroquine plus/minus primaqine is an inexpensive and highly effective treatment for uncomplicated P. knowlesi malaria infections. Primaquine is used as a gametocytocidal agent PFT�� to reduce transmission. However, with both chloroquine resistant P. falciparum and P. vivax in Borneo, misidentification of P. falciparum and P. vivax as P. knowlesi, or cryptic mixed infection could have dire consequences for the patient. Other antimalarials that have been used successfully in P. knowlesi malaria include mefloquine, quinine, atovaquone/proguanil and sulphadoxine-pyrimethamine ( Daneshvar et al., 2010). The artemisinin derivatives are likely to be highly effective but formal proof of this is awaited. In Peninsular Malaysia in the 1960s Anopheles hackeri was identified as the vector for P. knowlesi. As this mosquito is predominantly zoophagic and feeds mainly at the canopy level ( Cox-Singh and Singh, 2008) it was not thought to be important for transmission to humans-who rarely visit the forest canopy. However, recent work from Sarawak suggests that P. knowlesi

malaria is transmitted to humans from long-tailed (Macaca fasicularis) and pig-tailed (M. nemestrina) macaques by Anopheles latens mosquitoes when humans visit forested areas ( Vythilingam et al., 2006 and Tan Ketanserin et al., 2008). Tan et al. (2008) demonstrated that A. latens mosquitos were attracted to both humans and caged monkeys (probably Macaca fasicularis) and that forest-caught A. latens contained P. knowlesi sporozoites. Old World monkeys are conventionally divided into two subfamilies, the Colobinae and Cercopithecinae and both taxa contain diverse species in SE Asia. P. knowlesi has been found in the cercopithecine monkeys M. fasicularis and M. nemestrina and in a colobine monkey—the banded leaf monkey (Presbytis melalophos). However, there appears to be only one report of P.