Bacterium used to tackle Dengue fever

By Dr. Ananya Mandal, MDDec 9 2010

This January Australian scientists will start deploying a strange bacterium called Wolbachia pipientis in an attempt to halt disease transmission by mosquitoes especially Dengue fever. They are targeting the Aedes aegypti mosquito that transmits Dengue. Dengue is a viral disease that leads to high fever, severe muscle and joint pain and can also be fatal.

In recent studies, scientists have found that infection with Wolbachia makes mosquitoes resistant to the Dengue virus. Now, a team led by Scott O'Neill of the University of Queensland in Brisbane wants to test whether they can spread Wolbachia in the wild by setting free small numbers of mosquitoes infected with the microbe. Wolbachia also alters the reproduction of these mosquitoes making them multiply faster they said.

The experiments would be conducted in two towns in Queensland. Actual trial that would help would come after approval in Vietnam and Thailand where the disease is rampant they said. O'Neill said, “We wanted to start in our own backyard.” In another experiment a few weeks ago genetically sterile mosquitoes were tried on the Caribbean island of Grand Cayman.

Jason Rasgon, an entomologist at Johns Hopkins University in Baltimore, Maryland said both studies are groundbreaking. “If you had asked me 5 years ago when we would start releasing Wolbachia-infected mosquitoes, I might have said, ‘20 years from now,’ ” he said. Wolbachia lives inside the cells of more than half of all insect species, including many mosquitoes, but not the most important disease vectors. Female insects pass the bacteria on to their offspring via their eggs but when an uninfected female mates with an infected male, there are no viable offspring. This ensures a fast spread. O'Neill said this is simple with no genetic modification needed. Wolbachia has now become the weapon itself he explained. “You can think of it as a vaccine for mosquitoes,” he added.

As of now the team plans to release about 10 mosquitoes a week per household for 12 weeks. The goal is to find out how well the microbe spreads. Based on mathematical models, O'Neill thinks the infection could travel about 10 kilometers a year. Not every Ae. aegypti mosquito in the world will eventually become infected, he says. Geographical barriers keep separate populations apart. There is, of course, the possibility that mosquitoes or the pathogens will adapt to elude Wolbachi’s effects experts warn.