Aedes mosquitoes terrorize much of the planet. Their bites maintain worldwide epidemics as formidable as those of yellow fever, dengue fever, Zika or even chikungunya. By successively attacking a person who is already infected and then a healthy person, they – or rather they since only females bite – are the only vectors of these diseases.

With several tens of thousands of deaths to its credit each year, and millions of patients, the genus Aedes and its various species (aegypti, albopictus, etc.) are on the podium of the worst listed killers, behind the anopheles, mosquito vectors of malaria.

However, the Aedes would have enough to plead not guilty. In January 2022, a team from the Institute for Research and Development (IRD, Mivegec) in Montpellier, led by Julien Pompon, showed that once infected with the dengue virus, the animal lost part of the raison. It multiplies attacks, bites and transplants the same hosts, increasing the risk of transmission of the pathogen. Abolition or at least attenuation of discernment, could advance the defense.

Altered body odor

An article published on June 30 in the journal Cell will offer its lawyers a new argument: manipulation. A Chinese team has just demonstrated that flaviviruses (responsible for dengue fever and Zika), when they infect a human or a mouse, modify their body odor and make them irresistible to insects. No murder, therefore, just a crime of passion.

To demonstrate this, Chinese scientists first offered different Aedes species the choice between an infected mouse and a healthy mouse. Without hesitation, all opted for diseased rodents, dengue as Zika. The same result was observed with blotters impregnated with human sweat.

The researchers then tried to understand its origin. They therefore compared the volatile compounds present on the two types of skin, infected or not. Several molecules proved to be overabundant on the affected epidermis. All were then presented to mosquitoes. Listening to the researchers, one literally “freaked” them.

Chosen in spite of itself, acetophenone is produced by bacteria present on the skin. On healthy epidermis, bacilli are fought by antimicrobial peptides called RELMα. The Chinese team found that in diseased mice, peptides are rarer and bacteria thrive. “By repressing RELMα, the virus allows the proliferation of bacteria, therefore acetophenone which will attract mosquitoes”, summarizes Professor Dong Cheng, of the Tsinghua School of Medicine, who coordinated the research.

Vitamin A as a boost

“It’s a very nice study, very complete, which provides very concrete elements allowing us to better understand the complex mechanisms of vectorial transmission and to identify alternative avenues for their control”, greets the entomologist Frédéric Simard, director of the Mivegec laboratory, in Montpellier.

Chinese researchers have indeed tried to find a solution to this parasitic manipulation. They fed the mice a vitamin A derivative, isotretinoin, an anti-acne drug known to boost the production of antimicrobial peptides. With the cascading effect they were hoping for: more RELMα, less acetophenone, less mosquito bites.

Researchers are now waiting to see if isotretinoin also reduces production of the odorant molecule in humans. They are actually convinced of this and are already planning to provide patients with vitamin supplements, then to observe the circulation of the virus. Fighting a dengue epidemic with vitamin A: we can smile, but the test is scheduled in Malaysia, starting this fall.

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