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French, Thai scientists make dengue fever breakthrough

Aedes aegypti passes on dengue fever James Gathany

A team of French and Thai scientists has found that dengue fever is spread through a genetic interaction between mosquitoes and the virus that causes the disease.

Scientists with the French Pasteur Institute and Thailand’s Armed Forces Research Institute of Medical Sceinces published a paper Thursday with results of genetic tests on wild insects with four different types of the virus.

Dengue fever, which is carried by mosquitoes, is most common in the tropics but has now travelled to more temperate zones thanks to the effects of globalisation, air travel and climate change, experts say.

In a study published in the open-access journal PLoS Genetics, the researchers found that some mosquitoes of the main vector species, Aedes aegypti, are able to pass on the virus after sucking blood from an infected human but that others do not.

The answer lies in a genetic pairing between insect and virus, according to the paper.

"To some extent it depends on the specific pairing of mosquito and virus, so it’s hard to tell how exactly it works," Louis Lambrechts of the Pasteur Institute in Paris told RFI. "But we know that it is not only the genetic factors of the mosquitoes that determine transmission but also the combination of genetic factors of the mosquitoes and the viruses that are important."

After the mosquito feeds on an infected individual, the virus becomes established in the insect's mid-gut cells, then spreads throughout the rest of body.

The mosquito becomes infectious only once the virus reaches the salivary glands and is released into its saliva.

But the infection is established only when the right strain of mosquito meets the right train of dengue, according to the paper.

"We have found another layer of complexity, though it’s not going to help us prevent the disease," Lambrechts says. "But that’s how research works. We tend to oversimplify situations in the laboratory to study things, but of course when we go back to reality, it’s always more complex than we thought."

For now these findings are pure research but they could have implications for developing genetically-engineered, dengue-resistant mosquitoes.