Using Disease to Fight Disease

Most people probably wouldn’t want to visit a mosquito research lab on their family vacation, but Melinda and I were in Australia recently and were excited to see some amazing work in molecular biology that could lead to a breakthrough in controlling mosquito-borne diseases such as dengue fever.

Mosquitoes are a plague in much of the developing world, not just because they are a nuisance, but because they are transmission agents for some truly terrible diseases. The scientists we met with in Cairns have discovered a way to infect mosquitoes that are normally capable of carrying diseases like dengue and yellow fever with a bacterium called Wolbachia. Wolbachia is naturally present in many types of insects, but not in these mosquitoes. Although it is harmless to humans and most other animals, when placed in these mosquitoes Wolbachia shortens their lifespan by about 50 percent and inhibits the development of dengue virus and several other pathogens.

If mosquitoes with the Wolbachia strain can be successfully introduced into wild mosquito populations, it could greatly reduce the transmission of infectious diseases to humans because most mosquitoes would die off before the viruses that cause human disease could replicate in their body. Another plus for Wolbachia is that it alters the mosquitoes’ reproductive biology, so that when female mosquitoes that do not carry Wolbachia mate with male mosquitoes that do carry Wolbachia nearly all of their embryos die off. Since Wolbachia is passed through the mother mosquito to her offspring, this means that Wolbachia can spread very rapidly through a mosquito population.

Some of these discoveries were a surprise to scientists. If they can be proven in field trials, Wolbachia could create a cheap, natural, and self-sustaining method of control that dramatically reduces dengue fever and other major infectious diseases such as yellow fever and malaria.

The research, led by Professor Scott O’Neill of Monash University, has been funded since 2005 by the Foundation for the National Institutes of Health (FNIH) under the Grand Challenges in Global Health initiative, which encourages innovation to solve persistent health problems in the developing world. Diseases spread by mosquitoes are definitely at the top of that list.

O’Neill’s work is mainly focused on preventing mosquitoes from transmitting the virus that causes dengue fever, an infectious tropical disease that causes 22,000 deaths—mostly among children—and results in 500,000 cases of severe illness each year. Scientists are optimistic that this approach could also work with other insect-transmitted diseases such as malaria, which kills nearly 1 million people annually, mostly children under 5 years of age.

Historically, the battle against disease-carrying mosquitoes has relied on repellants, insecticides, bed nets and eliminating stagnant water breeding sites. More recently, scientists have been working on vaccines that would prevent people from getting infected with mosquito-borne diseases.

To do his current research, O’Neill has had to convince people in Cairns that releasing mosquitoes in their neighborhoods is a good thing. Melinda and I participated in one release of about 20 jars of mosquitoes—probably 1,000 mosquitoes in all. I was bitten by several dozen, but was safe from getting dengue fever because the mosquitoes being released were lab-reared and not infected with dengue. I have a lot of respect for the volunteers who go into mosquito cages and allow themselves to be bit in the name of science. The average number of bites they get is over 50!

It was fascinating to see the project first-hand. There’s a real possibility that this approach will get deployed broadly and could really help reduce a lot of disease transmission. But as exciting as it was for Melinda and me, our kids said they definitely didn’t mind not going along.