The Turgid Tale of the Tried and True Mosquito Den Net

By Michelle Vachon
The Cambodia Daily

Twenty years ago this month, a team of researchers introduced the insecticide-treated bed net for malaria control. This is the first of a three-part series on changes that its use brought to the fight against the disease.

Medical entomologist Pierre Carnevale and his research team suggested using insecticide-treated bed nets for malaria control in July 1984, based on successful results in keeping disease-carrying mosquitoes away from people, he said. 

But this new approach had to actually reduce malaria cases in order to become part of malaria-control programs, Carnevale said.

The researchers began testing treated bed nets in rice fields and swamp areas of Burkina Faso, where they were based. "We obtained results that were absolutely remarkable, showing a reduction in malaria transmission," Carnevale said. 

Such research presented a great deal of difficulties, said Jo Lines, an entomologist with the London School of Hygiene and Tropical Medecine, and the head of a British government's malaria research program. This meant following about 1,000 people over that area's peak malaria season to compare the number of malaria cases, he said. 

"Plus what we really wanted to know was whether or not it would protect children from severe malaria and fatal malaria." 

A series of small studies were followed by a large-scale one in Gambia, Lines said.

"The first Gambian [research] group was one of the strongest groups at the time in malaria field methodology in the world, " he said. That group had just completed an extensive study to find out how many children under the age of five died of malaria. 

So in the early 1990s, the Gambian group monitored about 20,000 people over two peak seasons to test treated nets. Their use reduced child mortality by more than half, even though the earlier study demonstrated that malaria was responsible for only a quarter of children's death under five, Lines said.

"This showed that a lot of the deaths that we would attribute, from the state of the child, to pneumonia, diarrhea or other conditions, that those conditions would not have been fatal if there had not been malaria as well," he said.

The Gambian tests were followed by four large-scale trials on treated nets in Africa supported by the World Health Organization's Tropical Disease Research Program. Results showed on average a 20-percent drop in child death, Lines said. 

Since then, treated bed nets have been widely used in Southeast Asia, and have been part of the National Malaria Center's strategy since the mid-1990s. 
Researchers in Cambodia and around the world continue to test mosquitoes' resistance to insecticides on bed nets. Experiments are being made with combination insecticides, Carnevale said.