LONDON (Reuters) - Deforestation in Malaysia and the changes it causes to the environment are highly likely to be to blame for a steep rise in human cases of a type of malaria usually found in monkeys, scientists said on Thursday.
The mosquito-borne disease, known as Plasmodium knowlesi malaria, is common in forest-dwelling macaque monkeys and was only recently found for the first time in people, the scientists said in a study of the issue.
Yet with widespread deforestation alongside rapid oil palm and other agricultural expansion, the disease has now become the most common form of human malaria in many areas of Malaysia, they said, and has been reported across southeast Asia.
In research published in the Emerging Infectious Diseases journal, scientists led by Kimberly Fornace of the London School of Hygiene and Tropical Medicine said their analysis showed that changes in the way land is used is a key driver in the emergence of P. knowlesi in people.
“The dramatic rise in the number of P. knowlesi malaria cases in humans in Malaysia in the past ten years has been most common in areas with deforestation, as well as areas that are close to patches of forest where humans, macaques and mosquitoes are coming into closer and more frequent contact,” said Fornace.
She said this suggests there is a higher risk of P. knowlesi transmission in areas where land use is changing.
“This knowledge will help focus efforts on these areas and also predict and respond to future outbreaks,” she added. “We view deforestation as having distinct public health consequences which need to be urgently addressed.”
The study focused on Malaysia’s Kudat and Kota Marudu districts, covering an area of more than 3,000 square kilometres with a population of approximately 120,000 people.
Fornace’s team used hospital records for 2008-2012 to collect data on the number of P. knowlesi cases from villages in the districts.
Satellite data helped the team to map the local forest, land use and environmental changes around 450 villages to correlate how these changes might affect human infection.
They found the number of P. knowlesi cases was strongly linked to deforestation around the villages.
This could be explained by a number of factors, they said, including people working in tree clearance and agriculture having closer contact with forest areas where macaques and mosquitoes live. Macaque populations are also becoming more densely concentrated in forests where people work.
Reporting by Kate Kelland; Editing by Tom Heneghan