Despite mosquito resistance, anti-malarial bed nets offer hope

Washington: A team of researchers has found that insecticide-treated bed nets may still help prevent malaria, despite mosquitoes developing resistance towards it.

These nets have contributed to the prevention of millions of deaths due to malaria, but in recent years, there has been growing concern that mosquitoes are becoming resistant to the pyrethroid insecticides used on the nets, making them less effective. However, the impact of this resistance on malaria as a public health problem has been harder to demonstrate, for reasons that remain unclear.

One possible reason is suggested by the London School of Hygiene & Tropical Medicine and Malaria Consortium study that although resistant mosquitoes are surviving contact with the insecticide, the malaria parasites inside those mosquitoes are affected by the chemicals.

The study was funded by UK Aid and carried out in Uganda, focusing on one of the main malaria carrying mosquitoes in Africa – Anopheles gambiae s.s. The 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.

The team 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.

Co-author Tarekegn Abeku said that 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.

Lead author Mojca Kristan said that 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. 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.

The study appears in Parasites & Vectors. (ANI)