A two-year study involving 10,700 people in Ratanakkiri province concluded that insecticide-sprayed bednets play a considerable role in reducing malaria cases, but that they are less effective at certain times of the year.
This is due to the fact that species of malaria-carrying mosquitoes vary in their biting habits, said Tho Sochantha, head of operational research at the National Malaria Center.
An dirus mosquitoes are at their most active late at night when people have slipped under their bednets, while An minimus mosquitoes attack around 7 pm, catching people before bedtime, he said.
As a result, the effect of bednets was more pronounced in June and July, during which An dirus mosquitoes are at their most numerous, and goes down in April and May, when An minimus abound, Tho Sochantha said.
The study compared villages using bednets to villages not using them.
In spite of seasonal fluctuations, researchers concluded that 520 cases were prevented because of bednets among the 6,100 people using them.
Comparing data for September 2001, when people were checked for malaria before net distribution, with September 2002, they noted a 44 percent decrease in malaria cases. During that same period, malaria cases had jumped 28 percent in the rest of the province.
The study, which was supported by the European Commission Malaria Control project in Cambodia that ended in December, included 36 hill tribe villages living in or near the forest. The study took place in that province because of the large number of malaria cases in that area. Mosquitoes thrive in that forest environment, Tho Sochantha said.
Malaria workers were put in every village to make sure that, in villages not using bednets, the disease would be detected and treated early if people were infected, Tho Sochantha said. Those volunteers received diagnostic dipsticks and pre-packaged combination treatments.
After dividing villages based on their vulnerability to the disease, the ones to receive bednets were selected at random.
The nets were distributed in November 2001. By June 2002, malaria cases had dropped 59 percent, and in July 54 percent compared to the same months the year before.
Studies on bednets had previously been conducted in Southeast Asia. However, they had been inconclusive due to their small scale or inappropriate study design, which prompted the National Malaria Center to launch this research in cooperation with the EC Malaria Project, the researchers said.
Malaria still kills hundreds of Cambodians each year, and millions worldwide are afflicted with the illness, which remains one of the world’s top killers.
Experts consider bednets the most effective measures against the disease.