Naturally acquired infections with Plasmodium knowlesi, the fifth human malaria, are growing [1]. Since 2004 increasing numbers of cases have been reported from residents and returned travelers predominantly from Malaysia and other countries in South-East Asia including Thailand, Vietnam, Myanmar, Singapore, Indonesia and the Philippines [2-8]. Cases coincide with the geographic distribution of its natural simian hosts (long-tailed and pig-tailed macaques) and Anopheles leucosphyrus group mosquito vector [9, 10], with potential human-to-human transmission unknown. Eastern Malaysia appears to be the epicentre, with around 1400 PCR-confirmed P. knowlesi human mono-infections reported in 2009, comprising 41% of 2,189 total malaria cases in Sarawak [11] and 343 cases from selected samples sent to Sabah's State Reference Laboratory [12]. P. knowlesi is also now the most common cause of malaria in different contrasting regions, including 70% of malaria admissions in the heavily forested area of Kapit in Sarawak [1, 13], 63% of samples from the interior division of Sabah [14], and in 87% of malaria admissions in the deforested coastal area of Kudat in Sabah, where it is also the major cause of malaria in children [15].