Microbial Warfare

Microbial Warfare

I recommend this "Not Rocket Science" article about a possible new approach to the control of mosquito-borne dengue fever. It's brief, but paints a vivid picture of some clever, flexible, and ethical thinking about how to design a more specific weapon than a broadcast pesticide. Some Australian scientists figured out a way to infect dengue-carrying mosquitos with a bacterium that attacks the dengue virus without much harming the mosquito. Before they settled on the final technique, they learned some clever tricks from the bacterium itself:

Wolbachia is transmitted in the eggs of infected females, so it has evolved many strategies for reaching new hosts by screwing over dead-end males. Sometimes it kills them. Sometimes it turns them into females. It also uses a subtler trick called “cytoplasmic incompatibility“, where uninfected females cannot mate successfully with infected males. This means that infected females, who can mate with whomever they like, enjoy a big advantage over uninfected females, who are more restricted. They lay more eggs, which carry more Wolbachia.

The scientists dreamed up a new approach of their own, too, in the form of

a strain that halves the lifetimes of infected females. Only older mosquitoes can transmit dengue fever because it takes several weeks for the virus to reproduce in the insects’ guts. If you knock off the older ones early, you could slash their chances of spreading disease.

That last gambit was not the one they settled on. Ultimately they got a line of mosquitoes going that would carry a Wolbachia strain that somehow killed off the dengue virus right in the mosquito gut. The bacterium can't be transmitted from adult to adult mosquito, though, only through offspring. So the scientists needed to release infected mosquitoes into a native population and let them breed.

Now this part is really interesting, I think. The scientists really wanted to test the new mosquitoes in Viet Nam, where dengue fever is endemic. Instead, they persuaded their neighbors in Queensland to be the first guinea pigs, even though the results would be harder to judge there because dengue fever outbreaks are only intermittent. They reasoned that they could not expect the Vietnamese to trust them to run the experiments there if they had not been willing to try them in their own backyard. As it turned out, the experiments in Queensland were quite successful in showing that an entire mosquito population can be quickly converted to Wolbachia carriers without ill effects. Now the team is headed to Viet Nam to see if they can show real progress in fighting dengue outbreaks.