Parasite’s jump from monkeys to people seems aided by deforestation
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NEW ORLEANS — A form of malaria found in wild monkeys has begun to infect people so often in parts of Southeast Asia that it has become the leading cause of malaria in Malaysia.
The Malaysian states of Sarawak and Sabah on the island of Borneo have shown a surge in infections with the parasite Plasmodium knowlesi, which is carried by long-tailed and pig-tailed macaques. P. knowlesi now accounts for nearly 70 percent of malaria cases in people there, Balbir Singh, director of the Malaria Research Center at the University of Malaysia in Sarawak, reported November 3 at a meeting of the American Society of Tropical Medicine and Hygiene.
Recent years’ surge in P. knowlesi infections has coincided with a stark increase in deforestation. Malaysia now ranks high among countries worldwide in the percentage of forest cover lost from 2000 to 2012, according to a 2013 study in Science. Singh said deforestation to convert forest land into oil palm plantations might be driving macaques into other habitat that’s closer to settlements. The mode of malaria transmission between monkeys and humans is unclear, he said.
Meanwhile, 101 of 108 wild macaques examined by his team harbored P. knowlesi. The parasite does not make macaques seriously ill, but the malaria it causes in humans can be severe and is more likely to be fatal than cases caused by other malaria parasites, Singh said.
Infection rates of P. knowlesi in mainland Malaysia are rising as well, Singh reported, and recent studies show P. knowlesi showing up sporadically across several Southeast Asian countries. One bit of good news: P. knowlesi is such a recent arrival in humans that it largely hasn’t developed resistance to antimalarial drugs, Singh said.
B. Singh. Origin and extent of zoonotic Plasmodium knowlesi infections. Annual Meeting of the American Society of Tropical Medicine and Hygiene. New Orleans, November 3, 2014.
M.C. Hansen et al. High-resolution global maps of 21st century forest cover change. Science. Vol. 342, November 15, 2013, p. 850. doi: 10.1126/science.1244693.
C.L. Moyes et al. Defining the geographical range of the Plasmodium knowlesi reservoir. PLOS Neglected Tropical Diseases. Vol. 8, March 2014, p. e2780. doi:10.1371/journal.pntd.0002780.