Molecular epidemiology of mosquitoes for the transmission of forest malaria in south-central Vietnam

Human infection caused by non-human primate malarial parasites, such as Plasmodium knowlesi and Plasmodium cynomolgi, occurs naturally in Southeast Asian countries, including Vietnam. Members of the Anopheles dirus species complex are known to be important vectors of human malarial parasites in the forested areas of southern and central Vietnam, including those in Khanh Phu commune and Khanh Hoa Province. Recent molecular epidemiological studies in Vietnam have reported cases of co-infection with Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and P. knowlesi in An. dirus. The commonly found macaques in the forest in the forested areas are suspected to be bitten by the same An. dirus population that bites humans. A recent epidemiological study identified six species of malarial parasites in sporozoite-infected An. dirus using polymerase chain reaction, of which P. vivax was the most common, followed by P. knowlesi, Plasmodium inui, P. cynomolgi, Plasmodium coatneyi, and P. falciparum. Based on a gametocyte analysis, the same allelic gametocyte types were observed in both humans and mosquitoes at similar frequencies. These observations suggest that people who stay overnight in the forests are frequently infected with both human and non-human primate malarial parasites, leading to the emergence of novel zoonotic malaria. Moreover, it is suggested that mosquito vector populations should be controlled and monitored closely.