A malaria parasite normally found in Southeast Asian macaques is now infecting people, causing severe and sometimes fatal disease. Until 2004, scientists believed only four malaria species naturally infected humans. *Plasmodium knowlesi* has since emerged as a fifth, but its true burden and the reasons for its jump to humans remain unknown. Early cases were linked to forest work, but recent infections in Malaysian Borneo occur where little forest remains. This project assembles a UK, Philippine, Malaysian, and Australian research network to identify the environmental, social, and biological factors driving human infection. Teams will compare high-risk Sabah (Malaysian Borneo) with lower-risk Palawan island (Philippines), studying macaques, mosquitoes, human behaviour, and landscape. They will produce risk maps and treatment guidelines for clinicians. If successful, the work will give health ministries in affected regions the data needed to target control measures—such as mosquito management or land-use planning—and prevent further outbreaks of this primate-origin malaria. The research is fundamentally about understanding a newly emerged zoonotic threat, with direct practical application for disease surveillance and public health policy.
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Malaria is caused by a single celled parasite found predominantly in the blood of its host, and is transmitted between hosts by the bite of a mosquito. Greater than 100 species of malaria exist, infecting many different animals. Until recently, humans were thought to be the natural hosts for 4 malaria species. However, since 2004 reports appeared of malaria infections in humans that are caused by a parasite species found previously in certain types of macaque in Southeast Asia. This species is Plasmodium knowlesi and, although benign in its natural monkey host, it has caused severe and even fatal disease in a proportion of human sufferers. Currently, we know little about the true burden of disease caused by this macaque parasite, or why it has emerged as a human pathogen. Initial descriptions of humans with Plasmodium knowlesi malaria suggested that they had been bitten and infected while working in forested areas, common in many countries of Southeast Asia. However, a more recent study in Malaysian Borneo shows that communities there are also being infected, even though there is little forest in existence. There may be a number of factors related to the environment, the types of mosquito in the area, people?s behaviour or movement and their proximity to troops of macaques that will have an effect on how at risk they are to being infected with Plasmodium knowlesi. We have built a network of researchers with different skills and expertise from the UK, the Philippines, Malaysia and Australia to tackle the various knowledge gaps by working together in a concerted approach. We plan to conduct studies in both the Philippines (on Palawan island) and in Sabah, a region of Malaysian Borneo. A larger number of cases of human Plasmodium knowlesi infection have been found in Sabah, compared to Palawan, and we will attempt to find out why communities here seem at higher risk. In treating their infections we can produce guidelines to help other clinicians faced with this disease. We also want to study the macaques, the mosquitoes that transmit the parasite, and the environment in which the infections occur to give us the whole picture and to produce maps that describe the risk factors existing in the different areas. We hope this will provide important information to ministries of health trying to control malaria disease in the affected regions and prevent further outbreaks of malaria originating from primates.
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