02 January 2009

Evolution applied: Biological warfare against mosquito-borne disease

ResearchBlogging.orgThis week's issue of Science starts the new year with an exciting application of evolutionary dynamics: a sort of biological warfare agent to control disease-bearing mosquitoes.

Even in the twenty-first century, mosquito-borne diseases like malaria and Dengue fever remain major public health challenges, particularly in the developing world. When vaccines are not available, the only way to prevent these diseases is to control the mosquitoes that spread them. Yet mosquito populations have evolved resistance to commonly-used pesticides, and others, like DDT, have dangerous environmental side effects.


Aedes aegypti, a disease-bearing
mosquito species

Photo by dincordero.
It's no wonder, then, that biologists are interested in ways to harness evolutionary population dynamics to reduce mosquito populations. McMeniman et al. take a big step toward this goal using the parasitic bacterium Wolbachia [$-a]. Wolbachia, which infects many other insect species, behaves like a "selfish gene" within its hosts. The bacterium is transmitted from females to their offspring, but not from males; so it induces infected females to lay more female eggs, and it kills the offspring of matings between infected males and uninfected females. This lets Wolbachia spread rapidly through populations, even if being infected is bad for the host.

Using Wolbachia against mosquitoes is not new; previously, people have discussed using genetically engineered forms of the bacterium to deliver agents that fight the diseases inside their carriers. But as McMeniman et al. describe, infection of the Dengue-bearing mosquito Aedes aegyptes actually already cuts the lifespan of the host in half. The Dengue pathogen needs time to incubate inside the mosquito host before it can be passed on to a human - longer, it turns out, than Wolbachia-infected mosquitoes typically live.

With this discovery, controlling Dengue or malaria could be as simple as introducing Wolbachia-infected female mosquitoes into at-risk areas, and monitoring the infection's spread. Together with common-sense public health measures like distributing mosquito nets and reducing standing water sources, Wolbachia has the potential to save and improve millions of lives.

References

C.J. McMeniman, R.V. Lane, B.N. Cass, A.W.C. Fong, M. Sidhu, Y.-F. Wang, S.L. O'Neill (2009). Stable introduction of a life-shortening Wolbachia infection into the mosquito Aedes aegypti. Science, 323 (5910), 141-4 DOI: 10.1126/science.1165326

A.F. Read, M.B. Thomas (2009). MICROBIOLOGY: Mosquitoes cut short Science, 323 (5910), 51-2 DOI: 10.1126/science.1168659

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