Despite many efforts toward the eradication of mosquito-borne illnesses, they still afflict tens of millions of people each year. However, recent findings suggest that the introduction of a common insect bacterium into natural mosquito populations may help prevent the spread of such diseases. In a December 2009 Cell publication, scientists reported that Aedes aegypti mosquitoes infected with the bacterium Wolbachia have significantly shorter life spans. According to the report, Wolbachia also increases A. Aegypti resistance to infection by the viruses that cause dengue fever and Chikungunya, two of the most common mosquito borne human diseases. Both diseases are characterized by rash and aching joints and are highly contagious, though Chikungunya has milder symptoms.

In the study, A. Aegypti mosquitoes, the primary natural carriers of both dengue and Chikungunya viruses, were infected with Wolbachia. The mosquitoes were then fed blood/virus mixtures containing either dengue fever virus or Chikungunya virus. After allowing several days for the viruses to take hold, infection levels were measured and found to be significantly lower for the mosquitoes with Wolbachia than for their control counterparts (those that lacked the bacterium).

According to the report, it is not yet known how Wolbachia confers resistance to certain viruses in A. Aegypti. Experiments suggest that the bacterium may strengthen the mosquito immune response to viral infection via changes in gene regulation. Stronger competition by Wolbachia for limiting resources inside the mosquitoes may also prevent viral infection.

"This might be very powerful in reducing pathogen transmission by Aedes aegypti to humans, particularly for dengue and Chikungunya," said Scott O'Neill, a professor at the University of Queensland. "Together with the previously described life-shortening effects, the results suggest we might be able to have a major impact on disease."

Each year, Dengue fever afflicts 50 million people and leads to tens of thousands of deaths, comparable to the 36,000 yearly deaths from seasonal flu in the US. There are currently no available cures or vaccines for dengue or Chikungunya. Previous prevention methods, many of which have depended on mosquito population control, have yielded mixed results. This study proposes a potential method for preventing human infection while maintaining natural mosquito populations, so as to avoid disrupting ecological systems.

Using closed greenhouses and computational models, O'Neill's group is currently examining how many infected mosquitoes would have to be released to spread Wolbachia in natural mosquito populations. Open field experiments may be launched within two years. If successful, these studies could culminate in widespread mosquito infection by Wolbachia, saving many human lives each year.

Sources:

http://www.eurekalert.org/pub_releases/2009-12/cp-nti122109.php

"Estimating Deaths from Seasonal Influenza in the United States." Centers for Disease Control and Prevention. 4 Sep. 2009. Accessed 12 Feb. 2010