Genetic Strategies for Controlling Mosquito-Borne Diseases
Engineered genes that block the transmission of malaria and dengue can hitch a ride on selfish DNA and spread into wild populations
Malaria kills more than a million people each year, primarily children under the age of six. Dengue fever is less deadly, but an outbreak can debilitate millions of people and easily overwhelm doctors and hospitals in tropical cities. To combat malaria and dengue, health agencies try to get rid of mosquitoes, which transmit both diseases. But a scarcity of resources hampers most control programs, and the insects are increasingly resistant to pesticides after decades of patchwork spraying. The disease organisms are evolving, too: The single-celled microbes that cause malaria are becoming resistant to widely used, inexpensive anti-malarial drugs such as chloroquine, which have been the first-choice treatment for malaria. (Drug therapies for dengue virus have never been available.) Many research teams are trying to develop vaccines for these diseases, but the complex biology of the two parasites—malaria is caused by four species of the protist Plasmodium, and four different viruses, or serotypes, can cause dengue—makes it difficult to predict whether vaccination will eventually confer broad immunity. And although pesticide-treated bed nets offer a promising low-tech means of preventing bites from malarial mosquitoes at night, the mosquitoes that carry dengue bite during the day.
To oppose these grim realities, several research teams (including our group at North Carolina State University) are now exploring a different approach to controlling the spread of mosquito-borne diseases, one that would reduce an insect's ability to transmit disease or would induce a population crash among selected disease-carrying species. How could either of these goals be achieved? By creating genetic changes in wild mosquitoes. Biologists have already extinguished other insect pests with genetic methods and in the laboratory have blocked the transmission of dengue and malaria in mosquitoes with engineered fragments of DNA. If scientists could breed some of those same genes into the wild mosquito population, the insect's bite might still be a nuisance—but it would no longer be a threat.