Preventing malaria with drug-treated mosquito nets

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In areas of the world where malaria is prevalent, mosquito nets save lives, especially treated mosquito nets. Over the past few decades, the mass distribution of insecticide treated bed nets has played a critical role in reducing the spread of malaria in endemic regions.

Even so, the number of malaria cases worldwide is still considerable: around 219 million cases of malaria are reported every year and more than 430,000 people die of the disease – many of them children.

To make matters worse, the insecticide resistance increases.

“Mosquitoes are amazingly resilient organisms that have become resistant to every insecticide that has been used to kill them,” says Flaminia Catteruccia, professor of immunology and infectious diseases at Harvard TH Chan School of Public Health.

In fact, some malaria hotspots have found near complete resistance to pyrethroid insecticides, which are widely used.

But what if we didn’t try to kill mosquitoes with malaria at all?

It doesn’t sound like intuitive, but Catteruccia and her colleagues wondered what would happen if bed nets were treated with an anti-malarial drug instead of insecticides. This way, the mosquitoes would stay alive but would not be able to develop and transmit Plasmodium falciparum (P. falciparum), the parasite that causes malaria.

To find out, the researchers coated a glass surface with the malaria compound atovaquone and then covered each surface with a cup. Female Anopheles mosquitoes were then placed in the cup so that they would come into contact with the glass each time they landed.

In some cases, the mosquitoes became infected with the malaria parasite immediately before being placed in the cup, and in some cases, the mosquitoes were infected immediately after removal. The researchers also varied the length of time the mosquitoes stayed in the cup and varied the concentration of atovaquone to which they were exposed.

It was found that relatively low concentrations of atovaquone (100 μmol per m2) were absorbed through the mosquito’s legs, completely blocking the development of the malaria parasite without affecting the mosquito’s reproduction or lifespan. In addition, this anti-malarial effect also occurred when the mosquitoes were only in contact with atovaquone for 6 minutes, which is roughly the time that wild mosquitoes rest on bed nets.

“When we put this data in a mathematical model that used real-world data on insecticide resistance, bed net coverage, and malaria prevalence, it was found that adding a compound like atovaquone to conventional bed nets can significantly reduce malaria transmission among almost all of the data we have for in Africa, “says Douglas Paton, lead author of the paper that is now published in Nature.

“What really excited us is that it also demonstrated that this new intervention would have the greatest impact in areas with the highest resistance to mosquito insecticides.”

Catteruccia explains that getting rid of malaria parasites in the mosquito instead of killing the mosquito itself is a great way to prevent the transmission of disease while avoiding insecticide resistance.

“Ultimately, using antimalarials on mosquito nets could help eradicate this devastating disease,” she says. “It’s a simple but innovative idea that is safe for people, using mosquito nets, and is environmentally friendly.”

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