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Scientists: Malaysian Deforestation Driving Spike in Malaria Strain

  • Henry Ridgwell

Deforestation in Malaysia is driving a sharp rise in human cases of a type of malaria normally only found in animals, scientists from the London School of Hygiene and Tropical Medicine say.

Researchers focused on a 3,000-square-kilometer area of Sabah state in Malaysia, with a population of 120,000 people. Much of the forest is being cleared to produce palm oil and other commodities.

Using hospital data and satellite mapping, scientists found the changes in land use were closely associated with a rise in the number of human cases of a type of malaria called Plasmodium knowlesi.

Professor Chris Drakeley, who was part of the research team, said the malaria's normal host, "the thing that it normally grows in, is long- and pig-tailed macaques. And in recent years in that part of Malaysia, northern Borneo, they have shown an increase in the number of cases in individuals with this malaria, presenting themselves to hospitals.”

Researchers said this was most likely explained by humans coming in close contact with the forest inhabited by the macaques, and the mosquitoes that transmit malaria. Many local villagers are employed in tree clearance and agricultural expansion.

The Plasmodium knowlesi strain is now the most common form of human malaria in many areas of Malaysia, and it has been reported across Southeast Asia.

“It can rapidly reproduce in your blood, and that means you get very high levels of infection," Drakeley said. "The case fatality rate, the number of people that die per infection, is quite high. We don’t think there’s going to be a very big expansion of it, but we’re very concerned as a general public health problem.”

So far there is no evidence of this strain of malaria being transmitted from human to human. But the report authors said their research suggested that deforestation has distinct public health consequences, which need to be urgently addressed.