Bacterial infection in mosquitoes renders them immune to malaria parasites

May 9, 2013, NIH/National Institute of Allergy and Infectious Diseases

Scientists funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, have established an inheritable bacterial infection in malaria-transmitting Anopheles mosquitoes that renders them immune to malaria parasites.

Specifically, the scientists infected the mosquitoes with Wolbachia, a bacterium common among insects that previously has been shown to prevent malaria-inducing Plasmodium parasites from developing in Anopheles mosquitoes. Before now, researchers had been unable to create mosquitoes with a stable Wolbachia infection that passed consistently from mother to offspring.

In this study, led by Zhiyong Xi, Ph.D., at Michigan State University, the researchers focused on Anopheles stephensi mosquitoes, the primary malaria carrier in the Middle East and South Asia. The scientists injected Wolbachia into male and female embryos of A. stephensi and, once they matured, mated the with uninfected male mosquitoes. A stable Wolbachia infection was maintained for 34 generations of mosquitoes, at which time the study ended. The researchers also introduced Wolbachia infection into uninfected adult mosquitoes in a series of experiments in which infected comprised 5 percent, 10 percent or 20 percent of the mosquito population. In all three experiments, 100 percent of the mosquitoes were infected within eight generations, supporting the potential of Wolbachia-infected mosquitoes as a malaria control strategy. Similar approaches have been used successfully to control dengue, another mosquito-borne disease, in certain settings.

This video first shows the process by which malaria is transmitted from mosquitoes to humans. It also shows the process by which populations of mosquitoes that carry the malaria parasite become infected with a bacterium called Wolbachia that acts like a vaccine, blocking malaria transmission. The Wolbachia-based approach for suppressing malaria demonstrated by Bian and colleagues in anopheline mosquitoes offers a highly promising tactic for integrated malaria control strategies in humans. Credit: Junmin Chen and Zhiyong Xi

In their examination of how Wolbachia affects Plasmodium parasites, the researchers found that the bacterium kills the parasites both in the mosquito midgut, where the parasites mature, and in the salivary glands, from which the parasites are transmitted to humans via . The scientists hypothesize that Wolbachia infection causes the formation of unstable compounds known as reactive oxygen species (ROS), which inhibit the development of the parasites. Future studies might examine whether Plasmodium can become resistant to ROS and explore ways to integrate Wolbachia-infected mosquitoes with existing strategies, the researchers write.

Explore further: Fighting disease from within the mosquito: New techniques to help halt the spread of disease

More information: Bian G et al. Wolbachia invades Anopheles stephensi populations and induces refractoriness to Plasmodium infection. Science. DOI: 10.1126/science.1236192 (2013).

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3 / 5 (1) May 09, 2013
A little confused. If Wolbachia kills the parasite in mosquitoes how does the human parasite infection get transmitted? Does Wolbachia also get transmitted? If so what happens to it? Have to admit the video is missing from the page and maybe my questions are answered there.
5 / 5 (1) May 10, 2013
The human malaria infection transmission is interrupted, the problem being that Anopheles for some reason doesn't easily transmit Wolbachia: "Before now, researchers had been unable to create mosquitoes with a stable Wolbachia infection that passed consistently from mother to offspring." If they had done so naturally, likely Wolbachia had crowded out the competition, which it seems it is geared towards.

Wolbachia is (so far, I think) an arthropod specialist. It is many times transmitted to the egg. It is even evolved into an obligate endosymbiont in a nematode species. [ http://en.wikiped...olbachia ]
3 / 5 (3) May 10, 2013
Your second question is answered on the forth bullet point.
Answer to the first question - it's doesn't get transmitted.
5 / 5 (1) May 10, 2013
Ha! It's that common and I didn't know about it. beleg & Torbjorn, thanks for the help.

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