The study was led by Professor Balbir Singh at the Malaria Research Centre, University Malaysia Sarawak, collaborating with Sarawak State Health Department, St George’s University of London and the London School of Hygiene and Tropical Medicine. Blood samples from 108 wild macaque monkeys, selected from 17 different locations, were examined for malaria parasites resulting in 5 species of Plasmodium being detected, with 78% of infection being P. knowlesi. By analyzing the circumsporozoite protein (csp) gene and the mitochondrial (mt) genome of P. knowlesi isolates from the macaque samples and human samples, some diverse alleles of the P. knowlesi csp gene and some mtDNA haplotypes are found to be present in both hosts.
The paper concludes that knowlesi malaria is primarily a zoonosis where the macaques are the preferred host acting as a reservoir.
Lee et al. Plasmodium knowlesi: Reservoir Hosts and Tracking the Emergence in Humans and Macaques. PLoS Pathog. 2011 Apr;7(4):e1002015. doi: 10.1371/journal.ppat.1002015. Epub 2011 Apr 7.