Insecticide-treated nets may still prevent malaria

Insecticide-treated nets may continue to remain partly effective in preventing malaria despite the mosquitoes developing resistance to the substances used on the nets, according to a study that for the first time observed effects of chemicals on malaria parasite inside a mosquito.
Researchers from London School of Hygiene & Tropical Medicine and Malaria Consortium have indicated that although resistant mosquitoes are surviving contact with the insecticide sprayed on the net, the malaria parasites inside those mosquitoes are affected by the chemicals.
"This is a significant result. It suggests that the use of insecticide-treated nets might continue to reduce malaria even in areas where the mosquitoes have become resistant. If so, that would give us more time to develop alternatives," said Tarekegn Abeku from Malaria Consortium.

"Our findings could help to explain why, so far, insecticide-treated nets seem to remain partly effective despite increasing resistance," said Jo Lines from London School of Hygiene & Tropical Medicine.
Researchers found that doses of the insecticide deltamethrin that are tolerated by resistant mosquitoes can interfere with development of the malaria parasite in the stomach of the mosquito.
"This is the first time that effects of pyrethroids on the parasite have been observed in a malaria endemic setting, with wild-caught mosquitoes and parasites," said Mojca Kristan from London School of Hygiene & Tropical Medicine.

"The next step is to show that the same thing happens not only when mosquitoes are forced into contact with the treated net, but also when they make contact naturally, as they attempt to feed on someone inside a net," Kristan said.

The Insecticide-treated nets have contributed to the prevention of millions of deaths due to malaria, but in recent years there has been a growing concern that mosquitoes are becoming resistant to the pyrethroid insecticides used on the nets, making them less effective.
The study was carried out in Uganda, focusing on one of the main malaria carrying mosquitoes in Africa - Anopheles gambiae ss.
They fed the mosquitoes on malaria infected blood, exposed some of them to the insecticide, and checked for parasite development a week later.
The proportion of infected mosquitoes was significantly lower in the group that had been exposed to the insecticide, and those that were infected developed fewer parasites than the unexposed group.

Insecticide resistance remains a major threat to malaria control, researchers said.
The findings were published in the journal Parasites & Vectors.