by Layne Cameron, Michigan State University
May 11, 2013 (TSR) – Mosquitoes are deadly and efficient disease transmitters, but they also can be equally good at spreading a cure for diseases they transmit, such as malaria, new research suggests.
A study in the current issue of Science shows that the transmission of malaria via mosquitoes to humans can be interrupted by using a strain of the bacteria Wolbachia in the insects. In a sense, Wolbachia would act as a vaccine of sorts for mosquitoes that would protect them from malaria parasites.
Treating mosquitoes would prevent them from transmitting malaria to humans, a disease that in 2010 affected 219 million people and caused an estimated 660,000 deaths.
“Wolbachia-based malaria control strategy has been discussed for the last two decades,” says Zhiyong Xi, a Michigan State University assistant professor of microbiology and molecular genetics.
“Our work is the first to demonstrate Wolbachia can be stably established in a key malaria vector, the mosquito species Anopheles stephensi, which opens the door to use Wolbachia for malaria control.”
First, Xi’s team successfully demonstrated how Wolbachia can be carried by this malaria mosquito vector and how the insects can spread the bacteria throughout the entire mosquito population. Secondly, researchers showed that the bacteria can prevent those mosquitoes from transmitting malaria parasites to humans.
“We developed the mosquito line carrying a stable Wolbachia infection,” Xi says. “We then seeded them into uninfected populations and repeatedly produced a population of predominantly Wolbachia-infected mosquitoes.”
The basis for Xi’s latest findings is connected to the success of his work using Wolbachia to halt Dengue fever. For this research, Xi focused on the mosquito species Aedes albopictus and Aedes aegypti. This work helped launch a global effort to develop Wolbachia-based strategies to eliminate dengue and other diseases.
The key to the malaria research was identifying the correct species of Wolbachia—wAlbB—and then injecting it into mosquito embryos. Out of the thousands of embryos injected by research associate Guowu Bian, one developed into a female that carried Wolbachia. The mosquito line derived from this female has maintained Wolbachia wAlbB infection with a 100 percent infection frequency through 34 generations. The number could grow higher as this is simply the last generation the researchers have bred thus far, Xi says.
The team then introduced various ratios of Wolbachia-infected females into a noninfected mosquito population. In each case, the entire population carried the bacteria in eight generations or less.
Using this promising approach to tackle malaria—the biggest vector-borne disease—gives scientists and world health officials another important tool to fight malaria.
Once Wolbachia has been released into a mosquito population, it is quite possible that it won’t need to be reapplied, making it more economical than other methods like pesticide or human vaccine. This adds special value to the feasibility of this control strategy, considering most of the malaria endemic areas are suffering from poverty, Xi says.
Additional scientists, including collaborators from Johns Hopkins University, also co-authored the paper.
The National Institutes of Health and Monash University grant from the Foundation for the National Institutes of Health through the Vector-Based Transmission of Control: Discovery Research program of the Grand Challenges in Global Health Initiative of the Bill & Melinda Gates Foundation funded the research. Xi’s research also is supported by MSU AgBioResearch.
DOI: 10.1126/science.1236192
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Eradicating Dengue Fever
Like malaria, dengue fever is an infectious disease transmitted by mosquitoes. Unlike malaria, there is no vaccine for it. As many as 100 million people contract dengue each year, but MSU researcher Zhiyong Xi is working to change that.
Among the estimated 2.5 billion people at risk for dengue, more than 70 percent live in Asia Pacific countries, which spurred Xi to establish a collaborative research institute at Sun Yat-sen University in Guangzhou, China.
Zhiyong Xi’s work on controlling malaria transmission developed out of the same research he’s done with Dengue fever. Xi’s work was featured in the 2012 President’s report, Spartans Will. 360. Visit http://report.president.msu.edu/360/
