By infecting mosquitoes with the bacterial species called Wolbachia, researchers have successfully stopped the malaria-causing parasite Plasmodium species from spreading to humans.
Caused by a parasite called Plasmodium, malaria is transmitted via the bites of infected mosquitoes. As the parasites proliferate in the human liver and then infect red blood cells, the tell-tale symptoms of fever, headache and vomiting appear between 10 and 15 days after the mosquito bite. Untreated, malaria can be life-threatening, as the vital organs and their blood supply are affected adversely. The currently available treatments are increasingly proving ineffective in many parts of the world, as the parasites develop resistance.
Researchers from Michigan State University (MSU), led by Zihyong Xi and his team, transferred Wolbachia into thousands of embryos of Anopheles stephensi, the mosquito that carries the malaria parasite. Starting with a single mosquito, the researchers successfully propagated the bacteria down 34 generations, with the result that the modified mosquitoes carried only a third as many parasites as the normal ones.
In a paper published in the journal Science, the investigators report that "in A. stephensi, Wolbachia strain wAlbB displays both perfect maternal transmission and the ability to induce high levels of cytoplasmic incompatibility. Seeding of naturally uninfected A. stephensi populations with infected females repeatedly resulted in Wolbachia invasion of laboratory mosquito populations." In addition, the mosquito infected with the strain wAlbB was resistant to the human malaria parasite Plasmodium falciparum, according to the report.
Until now, it was impossible to use Wolbachia for malaria control and establish successfully transformed mosquitoes, although Wolbachia as a symbiotic bacterium was successfully employed in controlling insect-transmitted disease. Wolbachia species have been shown to naturally infect insects such as butterflies and cockroaches. It has also been proven that Wolbachia infection in mosquitoes eliminates dengue fever .
"It's a very important study because they're the first group to show that Wolbachia can establish a stable heritable infection," said Jason L. Ragson of Pennsylvania State University, who did not work with Xi, but has been trying to lure Wolbachia bacteria into another species of mosquitoes for approximately eight years, according to Science News.
Malarial infection caused by A.stephensi is rampant in India and South Asia. Over 50 to 70 mosquito species worldwide are disease vectors, carrying five species of malaria parasite. According to Ragson's interview with Science News, the mechanism of inhibition still needs to be teased out, as blocking one species of malarial parasite may actually end up raising the transmission levels of others, for example in rodents.
The researchers therefore hope to carry out additional work to investigate the pathogen-blocking ability of the microbes, before releasing the Wolbachia-infected mosquitoes into the wild.
