Identification of Plasmodium infection in cynomolgus macaque and rhesus macaque monkeys in Thailand forests

Thailand is considered endemic for malaria. Recently, evidence was brought that humans can be infected by the simian Plasmodium namely P. cynomolgi and P. knowlesi. Therefore, the geographic range of positive malaria infection of non-human primates (NHPs), especially monkey species must be determined. The main objective of this study consisting of finding out how common malaria parasites are in monkey species. To achieve this, the researcher used quantitative PCR (qPCR) to detect overall Plasmodium spp., human and simian Plasmodium infection by using specific primers. A total of 472 monkey blood samples of cynomolgus macaque and rhesus macaque were collected from five different locations forests in Thailand. The analysis indicated that most of the samples were positive to different extents for Plasmodium infection regardless of the species of the parasite. As expected, the researcher did not detect any infection of monkeys by any of the human Plasmodium species. Furthermore, the researcher found many positive samples infected with P. cynomolgi and P. knowlesi. Surprisingly, mixed infection of P. cynomolgi and P. knowlesi occurred in 6 monkeys from three sampling sites. As result, the findings confirm P. cynomolgi and P. knowlesi-infected monkeys living in Thailand, suggesting high risk of zoonotic transmission of malaria.