Turning mosquitoes against dengue fever

It’s virtually a truism that prevention is better than cure. So how about preventing infection by dengue fever – a diseases that affects around 50 million people worldwide – by ridding it from mosquitoes first?

This is the ambition behind a bold new experiment conducted by Australian researchers as published in Nature today.

The idea emerged after noticing that the bacterium Wolbachia, a common endosymbiont that resides within the insect’s cells, interferes with RNA viruses in its host – viruses like dengue fever.

The next step was to find a strain of Wolbachia that didn’t impose a high fitness cost on the insect, which would prevent it from spreading through the population.

Researchers found that the strain wMel, a natural Wolbachia found in Drosophila, can block dengue virus while only having a slight fitness impact on the mosquito Aedes aegypti.

The bacteria also has an interesting feature known as cytopasmic incompatibility, which prevents infected male mosquitoes from successfully breeding with non-infected female mosquitoes. However, infected females can successfully mate – and pass on the Wolbachia - even with non-infected males.

As such, given a sufficient seed population, the frequency of Wolbachia-infected mosquitoes can rise to fixation, a phenomenon demonstrated by the researchers in the lab.

They then made the bold move of taking the study out of the lab and into the field by conducting a controlled five-stage release of Wolbachia-infected mosquitoes around Cairns in Queensland, an area riddled with mosquitoes.

In under 100 days, the Wolbachia-infected mosquitoes managed to out-breed non-infected mosquitoes to the point that Wolbachia infected reached fixation.

The upshot is: the mosquitoes around the release zones no longer carry dengue fever – and are quite likely free of other RNA viruses as well.

This is doubly enticing because Wolbachia also prevents the mosquitoes becoming infected with many other pathogens, including malaria and filarial nematodes.

As such, Wolbachia presents a novel and attractive form of natural disease control by preventing infection in the first place care of a naturally-occurring bacterium and without eradicating mosquitoes and altering the ecosystem.

The next phase will be to repeat the experimental release in other regions, notably those where dengue fever is endemic, such as in Southeast Asia or South America.

If successful, the approach might become a key means of managing diseases such as dengue fever and malaria by cutting it off at its source.

The paper, which involved researchers from the University of Queensland, the University of Melbourne, James Cook University, Monash University as well as North Carolina State University, the National Institutes of Health in the US and the Rockefeller University, was published in Nature today.