A Deadly Type Of Malaria From Monkeys Is Sweeping Malaysia

A Long Tailed Macaque. Chris McGrath/Getty Images

The majority of malaria cases in hospital in Malaysia are now caused by a dangerous and potentially deadly monkey-borne parasite once rarely seen in humans, researchers say.

And deforestation is the potential culprit in a growing number of infections which could allow the malaria strain to jump from macaque monkeys to human hosts, according to research presented at the American Society of Tropical Medicine and Hygiene annual meeting in New Orleans.

An analysis of malaria patients in Malaysian Borneo in 2013 showed that 68% had been sickened by Plasmodium knowlesi, says Balbir Singh, director of the Malaria Research Center at the University of Malaysia in Sarawak.

The parasite is increasingly associated with malaria deaths and is three times more frequent as a cause of severe malaria in Borneo than the more common P. falciparum parasite which is currently considered the world’s most deadly form of the disease.

The main host of knowlesi malaria has been the long-tailed and pig-tailed macaques found in the tropical forests of Malaysia and elsewhere in Southeast Asia.

The infections are concentrated in areas of Malaysia where over the last decade massive loss of native forest to timber and palm oil production has led to substantially increased human interactions with macaques.

“This is a form of malaria that was once rarely seen in people, but today, in some remote areas of the country, all of the indigenous malaria cases we are seeing are caused by the P. knowlesi parasite,” Singh says.

“If the number of cases continue to increase, human-to-human transmission by mosquitoes becomes possible. In fact, this may already have happened, which would allow P. knowlesi malaria to spread more easily throughout Southeast Asia.”

Evidence strongly suggests that victims of P. knowlesi malaria have been bitten by mosquitoes that had first bitten an infected macaque, making humans a dead-end host for the parasite.

However, recent research shows the parasite could change so that it can jump from person to person via mosquito bites, without requiring a monkey as part of its life cycle.

According to a 2013 study in the journal Science, Malaysia lost about 47,000 square kilometres of forest between 2000 and 2012, or about 14% of its total land area.

Singh said that P. knowlesi malaria is currently a major public health problem in Malaysia, as it is causing illness serious enough to require medical treatment in about 2,000 people a year.

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