Why I love science

May 7, 2009 at 2:45 pm Leave a comment

Malaria infects hundreds of millions of people every year, and kills millions. It’s caused by a parasite that infects two hosts during its life-cycle: mosquitoes and humans. Insecticides are widely used to kill the mosquitoes in infectious areas, and are very effective. And that leads to a problem: some mosquitoes happen to be immune to insecticides. They are trying to eat the same food (i.e. blood) as the regular mosquitoes, so the insecticides effectively remove their competitors, making their life easier. By the wonders of natural selection, the insecticide-resistant mosquitoes thrive.

Changing to a new insecticide just starts the same cycle again, providing a few years relief until the new insecticide-resistant mosquitoes emerge.

So now scientists have proposed a new approach, based on some detailed observations. The malaria parasite lives inside a mosquito for about 2 weeks, gestating and multiplying, until it moves into the salivary gland, and from there, into the next person the mosquito feeds from. This means that “young” mosquitoes are actually harmless to people, even if they happen to be infected. So the idea is to somehow only target “older” mosquitoes, who are actually likely to be infectious, rather than indiscriminately targeting “all” mosquitoes (but actually leaving the insecticide-resistant ones alone and healthy). One simple way to do this, the scientists suggest, is to simply reduce the dose of the insecticide, so that the mosquito needs to land several times on a treated bed-net or wall before getting a fatal dose. That way, the insecticide-resistant mosquitoes don’t have much of an advantage, as their regular competitors can still thrive. But the malaria parasites don’t get the chance to get into their human hosts. As an extra bonus, a lower dose would also be more likely to kill weaker mosquitoes than strong, healthy ones – i.e. it’s more likely to kill mosquitoes that are already infected with the parasite.

It’s a really simple idea, based on some close observations of the life-cycles of the parasites and mosquitoes, and some straightforward mathematical modelling (the last author on the paper is a mathematician, from the Open University, I see). No huge budgets, no epic time scales, just  a slight shift in thinking and actions that could save millions. (Subject to further research, of course.)

Read the details here:

How to Make Evolution-Proof Insecticides for Malaria Control Read AF, Lynch PA, Thomas MB PLoS Biology Vol. 7, No. 4, e58 doi:10.1371/journal.pbio.1000058

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