I’ve recently become convinced that effective malaria control in sub-Saharan Africa will require more than just bed nets and effective medicine. While these interventions will surely help, environmental modification to reduce the presence or virulence of mosquitoes, is essential. This is how malaria was eliminated in most countries where it has been successfully controlled, and I suspect indoor residual spraying (IRS) efforts have been key in many of the sub-Saharan African countries where potential success stories are brewing. These efforts get less attention from donors and researchers, perhaps because they are less visible, but also because spraying has accumulated its own set of baggage.

Spraying with insecticides is believed to adversely affect the environment. Anyone who knows anything about this will immediately think of DDT and Rachel Carson. While this is clearly a dark part of malaria control history, I gather that great efforts have been made to develop new insecticides that do not have the same environmental risks as some of the earlier generation products.

But spraying has an additional problem in that mosquitoes will develop resistance to the insecticide weakening their effectiveness over time. This is just one of those things, just like it is hard to develop antibiotics that don’t promote resistance in bacteria and drugs that don’t promote resistance for viruses. Where there are millions of them, there will always be a few that will figure out how to beat whatever we throw at it. Evolution always wins.

That is why a new idea by Andrew Read, Penelope Lynch, and Matthew Thomas is so interesting. They suggest that they can develop a “evolution-proof” insecticide for malaria control by realizing that it is really only older mosquitoes that transmit disease, usually well past the time when they have reproduced, so if we can target mosquitoes with an insecticide during the last phases of their life, than we can prevent transmission without inducing evolutionary pressure on the mosquito population. Kind of like the reverse logic of why late onset diseases like Huntington are hard to weed with evolutionary pressures.

Their proposition is based mainly on a modeling exercise that has shown that such an idea is feasible rather than promoting a product actually achieves this goal. But it does change the paradigm in our thinking about resistance and could pave the way to new products.

Thanks to Jack at Amherst for making me aware of this work in the economist.

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