Wolbachia pipientis, a common bacterium, can stop the dengue virus from multiplying in its mosquito host, effectively stopping the spread of dengue fever, researchers from the University of Queensland in Brisbane, Australia, reported in the journal Nature. Dengue fever, which is transmitted by the Aedes aegypti mosquito, kills approximately 12,500 people annually.

Bed nets are effective in controlling malaria, but not dengue, because the A. aegypti mosquito is active during the day. Worldwide concern regarding the mosquito’s progressive resistance to insecticides has triggered the search for alternative solutions.

Geneticist Scott O’Neill and team are convinced they have the solution. Not only can Wolbachia pipientis halt the virus’ replication within the mosquito, but it also spreads rapidly through the mosquito population.

O’Neill said:

“The presence of Wolbachia in mosquitoes completely blocks the ability of the dengue virus to grow in mosquitoes.”

Previous research by the same team had shown that the female mosquito’s lifespan can be reduced by 50% if it is infected with the Wolbachia strain wMelPop-CLA. They had intended to control dengue fever by bringing the infected mosquitoes to an early death, before the virus became mature enough to affect humans. The rate of reproduction of mosquitoes infected with the bacterium also dropped by 56%. However, the very short life span and other apparent advantages undermined the mosquitoes’ ability to pass the bacterium on.

In caged field studies, they found that mosquitoes infected with the wMel strain had similar lifespan and reproduction rates to uninfected mosquitoes. They detected no virus in the saliva of the infected females, suggesting that the bacterium was blocking disease transmission. As this strain did not harm the mosquitoes, it could spread more successfully to others in the wild.

Molecular entomologist Flaminia Catteruccia, from Imperial College London, whose work has focused on controlling the malaria-carrying mosquitoes Anopheles gambiae, said:

“It’s an environmentally friendly approach that does not affect the mosquitoes,
just the virus.”

O’Neill says they do not fully understand how wMel stops the virus from replication. They believe that the “bacteria compete for limited sub-cellular resources required by the virus for replication”.

The scientists released over 300,000 wMel-infected adult mosquitoes into the wild in two remote areas of Australia so they could mingle with wild A. argypti populations. After five weeks they found that virtually all the wild mosquitoes they tested were infected.

O’Neill said:

“This is the first case where wild insect populations have been transformed to reduce their ability to act as vectors of human disease agents,” the authors write. They now plan to run large trials over the next 2-3 years to test the approach in countries where dengue fever is endemic. If the trials go well, their method could be implemented as a control mechanism “immediately afterwards.”

Written by Christian Nordqvis