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A study part-funded by the European Research Council has found the first evidence of an intercellular bacterial infection in natural populations of two species of Anopheles mosquitoes, the major vectors of malaria in Africa.

The infection, called Wolbachia, has been shown in labs to reduce the incidence of pathogen infections in mosquitoes and has the potential to be used in controlling malaria-transmitting mosquito populations.

“Wolbachia is an interesting bacterium that seems perfectly suited for mosquito control. However, there were strong doubts that it could ever be used against field Anopheles populations,” said Flaminia Catteruccia, associate professor of immunology and infectious diseases at Harvard School of Public Health (HSPH), USA, and at the University of Perugia, Italy. “We were thrilled when we identified infections in natural mosquito populations, as we knew this finding could generate novel opportunities for stopping the spread of malaria.”

Anopheles mosquitoes are responsible for transmitting malaria, which causes more than 600,000 deaths each year and puts half of the world’s population at risk for diseases. Wolbachia infections spread rapidly through wild insect populations by inducing a reproductive phenomenon called cytoplasm incompatibility (CI), and 66% of arthropod species are infected. However, it was commonly thought that Anopheles mosquitoes were not natural hosts for Wolbachia infections, and attempts to identify infections in these mosquitoes in the field had failed.

Co-author Francesco Baldini, from University of Perugia and HSPH, in collaboration with researchers from CNRS, France, collected Anopheles mosquitoes from villages in Burkina Faso, West Africa, and analysed their reproductive tracts. Their objective was to identify all the bacteria in the reproductive systems of both male and female mosquitoes; they were not looking directly for Wolbachia. They found a novel strain of the infection, which they named wAnga.

The researchers say they can now investigate whether the wAnga strain shares properties with other Wolbachia strains, which could make control strategies possible by inducing CI and reducing Plasmodium (the parasite that causes malaria) numbers in Anopheles mosquitoes in the field.

The study appears online in Nature Communications.