Malaria mosquito dosed with disease-fighting bacteria

In a long-sought step toward building a safer mosquito, researchers have infected the insects with persistent bacteria that sabotage their malaria-causing parasites.

Researchers would like to use Wolbachia bacteria to keep malaria parasites from thriving inside a mosquito. In theory, a mosquito with the right bacterial infection could bite people without delivering the parasites that cause malaria.

Wolbachia naturally infect insects from butterflies to cockroaches — but not some disease-spreading mosquitoes. Years of effort have established Wolbachia in mosquitoes that spread dengue fever (SN: 7/14/12, p. 22), but the Anopheles species that carry malaria have been very difficult to infect.

At last, after a team led by Zhiyong Xi of Michigan State University in East Lansing injected Wolbachia bacteria into thousands of embryos of the mosquito Anopheles stephensi, one female caught a lingering case and started a laboratory line of infected offspring. The mosquito mothers have passed the infection down to 34 generations of offspring, the researchers report in the May 10 Science. The lineage carries less than one-third as many malaria parasites as uninfected mosquitoes do.

“It’s a very important study because they’re the first group to show that Wolbachia can establish a stable heritable infection,” says mosquito geneticist Jason L. Rasgon of Pennsylvania State University in University Park. Independent of Xi, Rasgon has been trying to coax Wolbachia bacteria into another malaria-carrying Anopheles mosquito for about  eight years.

The newly infected stephensi line is still in a proof-of-principle stage, Xi says. Before declaring Wolbachia-infected mosquitoes ready for release, he would have to see how they would block pathogens and compete for mates in the wild.

A. stephensi is one of the major mosquito menaces in India and South Asia; some 50 to 70 mosquito species worldwide carry malaria  parasites that infect people. In total, the insects carry four species of malaria parasite. Rasgon found that a Wolbachia strain that can block one species of human malaria parasite in the mosquito he works with actually increases the numbers of another malaria parasite, one that attacks rodents. So he’d like to know how Wolbachia that blocks one species of human malaria affects the others.