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Fungus to control Dengue mosquitoes

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Australian researchers have found fungus Beauveria bassiana could effectively kill Aedes aegypti, the mosquito responsible for spreading dengue. The results of the latest study by Jonathan Darbro of the Queensland Institute of Medical Research in Brisbane, Australia and his colleagues offer a potential alternative to pesticides to control mosquito-borne viral disease, reports The Scientist.

Yellow fever mosquito Aedes aegypti (Image courtesy: Wikimedia)

The fungus, which grows naturally in soil and is an insect parasite, is currently used to control a number of agriculture pests and recent studies have shown it may also kill dengue-carrying mosquitoes. But so far, there has only been one field study of the fungus on dengue-carrying mosquitoes, so its efficacy to temperature and humidity variations is yet to be verified.

Dengue is a viral disease transmitted by mosquitoes that infects between 50 and 100 million people annually, according to the World Health Organisation. Current control mechanisms rely heavily on insecticides, but recent reports of mosquitoes acquiring insecticide-resistance in Mexico have raised concerns about the effective management of the disease.

Darbro and his colleagues tested the fungus under laboratory and “semi-field” conditions in which the mosquitoes were housed in large cages in an area in Australia, where dengue is endemic. In the lab trials, fungal-infected mosquitoes were 30 per cent less likely to bite humans than controls and laid fewer eggs over their lifetime, similar to previous lab findings with other disease-carrying mosquitoes and other fungi. And in both the lab and semi-field trials, the fungus increased the mortality rate of infected mosquitoes by 88 per cent in the lab and between 59 to 95 per cent in the field.

“This has been an important step towards confirming what we see in the laboratory, we also see in the field,” said Darbro, noting that the fungus killed mosquitoes “equally well” in both lab and semi-field conditions, albeit more variably in the latter.

The challenge for scientists, however, is to ensure humans aren’t harmed by the fungus. But Darbro isn’t worried. While a small number of people, often with weak immune system, bas been infected by the fungus, he said, they have always been successfully treated.

Another hurdle to be overcome is developing a way successfully to infect the mosquitoes with the fungus. “That’s a million dollar question,” said Darbo. “The challenge is finding a place to put the fungus where the mosquitoes will land on it and get infected.”

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