Self-destruct gene could cut mosquito population

Late at night, many people hear the mosquito truck spraying insecticides to control the mosquito population in their neighborhood. Imagine instead that truck releasing genetically modified mosquitoes, ones that can kill off their natural born, disease-carrying twin.

That’s already happened on Grand Cayman Island and in Malaysia where the local mosquito carries the dengue fever virus — which can produce high fever, excruciating joint pain and even death. In both locations, modified male mosquitoes were released into the environment. These mosquitoes carry a self-destruct gene that they pass on to their offspring when modified males mate with wild females, and these offspring die before becoming adults.

On Grand Cayman Island, where they have Aedes aegypti, a mosquito that carries and transmits the dengue fever virus, for every natural male, 10 modified male mosquitoes were released, or a total of 3 million modified mosquitoes. As a result, a wild female is more likely to mate with a modified male, thereby producing self-destructing offspring.

In just four months, the entire mosquito population in the test area was reduced by 80 percent, according to the study led by Hilary Rankin of the Liverpool School of Tropical Medicine.

The second approach is really clever. Scientists discovered that mosquitoes infected with a bacterium called Wolbachia pipientis become resistant to carrying the dengue fever virus. They not only become resistant themselves, but pass these intracellular bacteria to their offspring, making them resistant as well.

During a recent field study in northern Australia by the country’s Monash University, scientists released a comparatively small number of 10,000 to 20,000 Wolbachia-infected mosquitoes weekly for 10 weeks. Six weeks after the final release, all the mosquitoes in the area that were sampled were infected. This means, at least in the test area, the risk of people getting dengue fever from mosquitoes should have declined.

Scientists have done further studies with Wolbachia-infected mosquitoes and found they may also be effective in controlling the spread of other deadly viruses and parasites such as malaria. Since malaria kills more people in the world than any other infectious disease, this approach may have a huge impact.

While exciting and humanitarian, this approach faces some tough opposition. A number of groups are against modified insects because there’s no way to tell what impact they could have on the local ecology. They wonder if modified mosquitoes would be better at survival and grow to unmanageable numbers, or if the modified mosquitoes could cause a collapse of the mosquito population and affect the population of animals or insects that feed on them.

Groups against modified mosquitoes also criticize companies and government agencies that allow field tests without appropriate oversight, claiming the tests are done without an opportunity for comment.

While their concerns are legitimate, scientists will undoubtedly continue trying to make modified mosquitoes more effective because of their life-saving potential.

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professors Norbert Herzog and David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at www.medicaldiscoverynews.com.