Insecticide 'wallpaper' lethal to malaria mosquitoes

Rows of experimental huts in Benin

Armel DJENONTIN CREC/IRD 2008

[COTONOU] 'Wallpapering' huts with sheeting made from insecticide-treated plastic could be a new tool for malaria control, research in Benin shows.

When used in combination with insecticide-treated bednets (ITNs) in hut trials, the sheeting killed all mosquitoes, and completely prevented bites. Results were published last week (20 October) in the Malaria Journal.

Researchers investigated the effectiveness of the sheeting in an attempt to counter the growing problem of resistance shown by Anopheles gambiae — Africa's main malaria mosquito — to the insecticide pyrethroid, which is used in bednets. Resistance is particularly strong in West Africa.

Indoor residual spraying (IRS) of home walls with insecticides — the other main control method — brings its own set of problems.

"Spraying requires frequent applications, which is costly, and it also threatens children's health due to toxic emanations," Vincent Corbel, study co-author and entomologist at France's Institute for Development Research (IRD), told SciDev.Net.

Corbel and his team turned their attention to plastic sheeting because it gives a coverage similar to spraying and can be impregnated with the insecticide carbamate.

In the laboratory, the researchers found that rice sacks woven from polypropylene fibres killed all mosquitoes and the insecticide persisted after the sheeting was washed.

In subsequent field trials, volunteers slept overnight in experimental huts in southern Benin, using various combinations of control methods. The mosquitoes they were exposed to were all pyrethroid-resistant.

In huts with plastic sheeting combined with mosquito nets, all mosquitoes died and none took a blood meal. Moreover, mosquitoes were seen to rest on the walls, indicating little irritation despite their body's absorption of the lethal insecticide.

Even in huts where only the top third of walls was covered by carbamate — to prevent contact with children — 80 per cent of mosquitoes were killed.

"Carbamate and pyrethroid interact [to kill] both resistant and non-resistant mosquitoes," says Corbel.

Armel Djenontin, a research student with the IRD, believes rural communities will find wallpapering a more practical malaria tool than wall-spraying. "Plastic sheeting won't need to be treated again for at least two years," he says.

Dorothée Kindé-Gazard, a parasitologist at Benin's University of Abomey-Calavi, is enthusiastic about the study's results but warns that funding availability and feasibility will need to be assessed before the technique can be implemented.

Link to full article in the Malaria Journal