For years, researchers have been altering mosquito genetics in an attempt to halt the malaria parasite’s lifecycle in the insect before it can spread the disease. But getting the modified gene or genes to spread through a population of mosquitoes has proved to be an intractable problem. Now, researchers at the Johns Hopkins Bloomberg School of Public Health are taking a different approach—introduce malaria-thwarting genetic changes into mosquito commensal flora.
“We thought that it would be easier to introduce bacteria than genes into mosquitoes in the field,” Marcelo Jacobs-Lorena told the blog Not Exactly Rocket Science (authored by Ed Yong, a regular contributor to The Scientist). Plus, the mosquito gut is the site of the malaria parasite's reproduction, a particularly vulnerable stage of Plasmodium's lifecycle.
Jacobs-Lorena and his team chose to work with Pantoea agglomerans, a harmless bacteria common to the mosquito gut, engineering it to fight the Plasmodium parasite. When the researchers introduced the engineered bacteria into mosquitoes in the lab, they found that the number of Plasmodium oocysts, the sporozoite-manufacturing cells that reside in the mosquito gut, were 85 to 98 percent lower than in uninfected mosquitoes. Fewer than 20 percent of the engineered mosquitoes acquired an infection after drinking a contaminated blood meal.
Once again, however, the challenge will be to introduce the bacteria into wild populations of mosquitoes where malaria is still a persistent killer. This problem is compounded by the fact that the engineered bacteria, working hard to produce antimalarial factors, may be less fit than the other commensals in the mosquito gut. “Mosquitoes would therefore have to be continuously exposed to large numbers of these GM bacteria in the field, for the bacteria to stand any chance of becoming a major portion of the microbes that reside in the mosquito gut,” George Dimopoulos, also of the Johns Hopkins Bloomberg School of Public Health told Not Exactly Rocket Science.