Dengue fever is a viral febrile disease caused by flaviviruses carried by the Aedes aegypti mosquito vector. It affects tens of millions of people per year, primarily in tropical and African countries. The primary mode of prevention is through mosquito control, but typical mosquito control measures, such as using bed nets and draining areas of standing water, are less effective against A. aegypti mosquitoes because they are day-biters and thrive in urban areas.

Now, a group of researchers from University of Queensland (Brisbane, Australia) reports success with a new method of mosquito control: shortening mosquito lifespan via infection with the bacterium Wolbachia pipientis. Because the virus that causes dengue requires an incubation period of about 2 weeks in its mosquito vector before it can infect humans, only older mosquitoes pose a potential dengue threat. Shortening the lifespan of infected mosquitoes may thus be an effective means of reducing dengue transmission.

Wolbachia bacteria infect a range of arthropods. They require female hosts in order to survive and have developed certain strategies to increase the prevalence of females in their host populations. One such mechanism is cytoplasmic incompatibility, in which matings between uninfected females and infected males produce no offspring. These strategies enable Wolbachia sp. to spread rapidly in host populations. Paired with its ability to shorten lifespan, this characteristic makes W. pipientis a potentially valuable tool for controlling insect populations. Unfortunately, Wolbachia sp. do not naturally infect A. aegypti.

The University of Queensland researchers, led by Scott O'Neill, looked to circumvent this obstacle. They chose a strain of W. pipientis that normally infects Drosophila melanogaster fruit flies and causes them to die early. Initial attempts to infect A. aegypti with W. pipientis were unsuccessful, so O'Neill's group adapted the bacterium by culturing it with mosquito cells for 3 years. The adapted W. pipientis successfully infected female A. aegypti and reduced the mosquitoes' lifespan by half, from 60 days to around 30 days (Science 323, 141–144; 2009). W. pipientis infection was stable. O'Neill's team then screened larvae from infected A. aegypti females to evaluate the maternal transmission rate of W. pipientis and found that it was very high (>99%).

These results suggest that infection with W. pipientis could be an effective means of controlling A. aegypti populations and the transmission of dengue fever. Scientists caution, however, that field studies are needed to determine how well this approach might work under more natural conditions.