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Nerissa Hannink

University of Melbourne media office

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By infecting mosquitoes with bacteria from flies that commonly live in kitchen fruit bowls, researchers have stopped the insects spreading the dengue virus.

The work was conducted by an international team of scientists from the Eliminate Dengue program, and was published today in two papers in the journal Nature. Co-authors include researchers from the University of Melbourne, Monash University and James Cook University.

The second paper also shows how the fruitfly bacteria was established in wild mosquito populations, offering a practical and inexpensive way to stop transmission of dengue fever which affects 50 million people annually.

The strain of dengue-blocking bacteria, called wMel Wolbachia, was first discovered in Australian fruit flies in 1988 by Professor Ary Hoffmann from the Bio21 Institute and the Department of Genetics, University of Melbourne.

“It is amazing that Aussie fruit bacteria can effectively immunise mosquitoes against dengue, thereby preventing its spread to humans,” Professor Hoffmann said.

“Our finding has the potential to halt the spread of the dengue virus which is vital as there is currently no vaccine and the geographical areas of infection are growing.”

The World Health Organisation ranks dengue fever as the most important mosquito-borne viral disease in the world, with an estimated 2.5 billion people living in dengue infected areas. The dengue virus mainly causes extreme fatigue and fever, but it kills around 1 in 500 infected people, mainly children. There have been around 2,400 cases of dengue infection in Northern Australia in recent years.

Other Wolbachia bacteria strains live naturally inside around 70% of all insects and are known to protect them against viral infection. But the team is the first to introduce the particular wMel Wolbachia strain into disease-carrying mosquitoes, and to establish it in natural populations during field trials in Queensland, Australia.

“This Wolbachia strain is important because after years of experiments, it is the first one trialed that does not have any major side effects for the mosquito to carry and is able to survive through the dry season. Wolbachia rapidly infects the wild mosquito population because it is inherited directly from the mother through the egg,” Professor Hoffmann said.

“Current control methods, mainly based on insecticides are failing to stop the global dengue problem and some mosquitoes are developing resistance. The benefit of the Wolbachia control method is that it is a cheaper biological control that communities could employ themselves, without using insecticides.”

Following years of community engagement and their overwhelming support, in January this year mosquitoes carrying Wolbachia were released in the Cairns suburbs of Yorkeys Knob and Gordonvale.

Within three months, 100% of the mosquitoes at Yorkeys Knob and 90% in Gordonvale carried Wolbachia.

“These findings tell us that Wolbachia-based strategies are practical to implement and might hold the key to a new cheap and sustainable approach to dengue control, an approach that should be particularly suited to large cities of the developing world,” Professor Hoffmann said.

The program will next undertake further trials in Cairns to test how well Wolbachia spreads across less contained areas than the initial trial sites. The team also aims to conduct trials in areas with endemic dengue infection such as Thailand, Vietnam, Brazil and Indonesia to directly determine the effectiveness of the method in reducing dengue disease in human populations.