The majority of malaria hospitalisations in Malaysia are now caused by a dangerous and potentially deadly monkey-borne parasite once rarely seen in humans, an Indian-origin researcher has found.
The study also found that deforestation is the potential culprit in a growing number of infections that could allow this virulent malaria strain to jump from macaque monkeys to human hosts.
An analysis of malaria patients hospitalised in Malaysian Borneo in 2013 showed that 68 per cent had been sickened by Plasmodium knowlesi, said 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 that 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.
That puts knowlesi malaria in the company of a growing list of dangerous emerging and re-emerging diseases - including Ebola and AIDS - that are being passed from animals to humans as development peels back more and more layers of tropical forest previously uninhabited by humans, researchers said.
"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 said.
"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," he said.
Evidence to date has strongly suggested 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 suggests that 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.
P knowlesi is the fifth species of malaria known to infect humans in nature. The parasite causes only mild malaria in macaques, Singh said, but in people it is the fastest replicating malaria parasite, multiplying every 24 hours in the blood.
The research was presented at the American Society of Tropical Medicine and Hygiene (ASTMH) Annual Meeting.
