Deforestation Rids Areas of Malaria-Spreading Mosquito

When teams from the National Malaria Center and Medecins sans Frontieres Belgium traveled to Pailin’s Tiek Chenh village in July for a five-month study of the area’s mosquito population, they found a forest village swarming with disease-bearing mosquitoes.

In September and October, the height of the mosquito season, the air was so heavy with insects that villagers were averaging about 35 bites per night, Dr Tho Sochantha, a malaria center entomologist, said Tuesday.

But when the teams returned to the village for a follow-up survey this month, they found that nightly bites had dropped to near zero. The decline is partly because of the dry season, Tho Sochantha said. But the radical decline in mosquito bites is mostly due to one key change in the environment—in only four months nearly 80 percent of the forest had been stripped away.

“We were surprised,” Tho Sochan­tha said of the abrupt change in the landscape.

Deforestation in that area has proceeded at a “quite staggering rate,” said Mike Davis of the forestry watchdog Global Wit­ness, as villagers have cleared the trees to make room for farm land.

Tho Sochantha said this was the first instance that he could remember in which Cambodia’s rampant deforestation had such a profound effect on the disease.

The teams will return to Tiek Chenh, located about 20 km from Pailin city in Stung Kach commune, Sala Krao district, for one week each month until July. Biting rates will likely increase when the rainy season starts, Tho Sochan­tha said. But the altered landscape has changed the nature of the disease in Tiek Chenh.

About 700,000 people living in forested areas in the country are at risk for malaria, according to the malaria center, and the villages in and at the edges of Pailin’s forests are some of the most malaria-ridden areas in the country.

The forest is home to the Anopheles dirus mosquito, the main transmitter of malaria to hu­mans in Cambodia, said Dr Bart Janssens, medical coordinator with Medecins sans Frontieres.

“This is a mosquito that loves to breed in small stagnant waters in leaves and between trees,” Jans­sens said Wednes­day. The bug flourishes in the forest and bites at night, leading to staggeringly high infection rates among loggers, farmers, hunters and others who work in the forest.

More than 20 percent of men older than 15 tested positive for malaria in a population screening conducted by the malaria center and Medecins sans Frontieres in their visit to the municipality last year. In contrast, 11.4 percent of adult women and 6.8 percent of children under 5 were found to have malaria.

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