Plasmodium knowlesi is a zoonotic malaria parasite normally residing in long-tailed and pig-tailed macaques (Macaca fascicularis and Macaca nemestrina, respectively) found throughout Southeast Asia.
The prevalence of malaria parasites, including those that are transmissible to humans, varied among all sampled regional populations of long-tailed macaques in Southeast Asia.
The emergence of resistance to artemisinin derivatives in Southeast Asia, manifested as delayed clearance of Plasmodium falciparum following treatment with artemisinins, is a major concern.
In western Cambodia, where artemisinin-based combination therapies are failing, the 6-day course of antimalarial therapy was associated with a cure rate of 97.7% (95% confidence interval, 90.9 to 99.4) at 42 days.
These threshold conditions are discussed in the context of malaria vector-parasite co-evolution as a function of anthropogenic effects.