Mosquitoes! We hate them. They give you these excruciatingly itchy and annoying bites that sometimes leave you scratching for days, they make that maddening buzzing sound when they fly around about to bite you, and they are just generally a nuisance. In addition, I’m sure we have all heard about the unpleasant pathogens mosquitoes help transmit between humans, like Plasmodium protozoa (which cause Malaria), Zika, and the West Nile, characterized by the high fevers and whole-body discomfort they cause (diarrhea, joint and muscle pain… ugh!). One of the most notorious mosquito species is Aedes aegypti, also known as the yellow fever mosquito. It can spread yellow fever, as its name suggests, but its repertoire is not limited to just that: it’s able to transmit many other disagreeable ailments as well, like chikungunya and dengue. These diseases affect a large number of people, especially dengue—which causes 96 million infections annually, of which 40,000 die. 

Our “bio-weapon” of choice is a bacterium from the genus Wolbachia. They are usually intracellular parasites, which means they take advantage of their hosts from within the latter’s cells. It’s estimated that more than 60% of all insect species (there are millions of them!) can be potential hosts of Wolbachia. Aedes aegypti is actually an exception, as there doesn’t seem to be a species of Wolbachia that infects it—that is, until scientists infected their eggs with strains of Wolbachia that usually infect other insects, such as fruit flies. 

When uninfected male mosquitoes mate with uninfected females, they produce uninfected offspring like normal. However, if an uninfected female mates with an infected male, all their offspring will die before hatching, due to a phenomenon dubbed “cytoplasmic incompatibility.” If an infected female mates with a male, infected or otherwise, she produces eggs that hatch into offspring that are all infected with Wolbachia. This means that, if infected mosquitoes of both sexes are released, the proportion of individuals infected with Wolbachia in that area increases dramatically. This method is also self-sustaining, and usually only requires an initial release of mosquitoes, as the females will pass the bacteria on to their offspring. 

How is this helpful, I hear you ask? Well, it turns out that the Wolbachia in Aedes aegypti greatly reduces the ability of the mosquito to transmit the unpleasant pathogens mentioned above to humans. Scientists are still not quite sure why this happens, but it has been shown that mosquitoes carrying Wolbachia have a reduced viral load—meaning it’s less likely to pass the pathogen to a human when biting them—even while carrying multiple viruses at once! This means that the transmission can be reduced without needing to reduce the frequency of bites, saving the hassle of the usual procedures like spraying the environment with harmful chemicals, covering puddles with water, and having to sleep in a big net. 

Breeding, infecting, then raising mosquitoes to release them into regions where the very same mosquitoes are causing issues may seem like an overcomplicated strategy, but it’s functional, and may even be better than traditional methods. Many of the above diseases, like dengue or Zika, don’t have effective treatments or vaccines, and outbreaks of these diseases often occur in tropical areas that may have poor access to modern healthcare, so those medical options will likely be ineffective even if they are developed. Using mosquitoes may well be more suitable!