Viruses spread by mosquitos because they make us smell tastier

By Stephen Beech via SWNS

Some viruses are spread by mosquitos because they make us smell tastier to the insects, reveals a new study.

Dengue and Zika viruses alter the microbiome in both mice and humans to attract mosquitoes and spread to new hosts, according to the findings

The disease viruses alter the scent of mice and humans they infect, according to the findings published in the journal Cell.

The altered scent attracts mozzies, which bite the host, drink their infected blood and then carry the virus to its next victim.

Dengue is spread by mosquitoes in tropical areas around the world. It causes fever, rash, and painful aches, and sometimes hemorrhage and even death.

More than 50 million dengue cases occur every year, and about 20,000 deaths, most of them in children, according to the National Institutes of Health (NIH) National Institute for Allergy and Infectious Disease.

Zika is another mosquito-spread viral disease in the same family as dengue. Although it is uncommon for Zika to cause serious disease in adults, a recent outbreak in South America caused serious birth defects in the unborn children of infected pregnant women.

Yellow fever, Japanese encephalitis, and West Nile are also members of the same virus family.

The viruses require ongoing infections in animal hosts as well as mosquitoes in order to spread.

An international team of researchers suspected that dengue and Zika might be manipulating the hosts in some way to attract mosquitoes.

They explained that both malaria and general inflammation can change people’s scents. Viral infection by dengue and Zika, they thought, might do the same thing.

The team tested whether mosquitoes showed a preference for infected mice. They found that when mosquitoes were offered a choice of healthy mice or mice sick with dengue, the mozzies were more attracted to the dengue-infected mice.

Then they analyzed the smelly molecules on the skin of infected and healthy mice. They identified several molecules that were more common in infected animals and tested them individually.

They applied them both to clean mice, and to the hands of human volunteers, and found that one odoriferous molecule, acetophenone, was especially attractive to mosquitoes.

Skin odourants collected from human dengue patients showed the same thing: more attractive to mosquitoes and more acetophenone production.

Project lead scientist Professor Gong Cheng, of Tsinghua University, China, said: “Mosquitoes rely on their sense of smell to detect hosts and guide fundamental behaviors of survival.

“At the beginning of this study, we found that the mosquitoes preferred to seek and feed on dengue and Zika-infected mice.”

Study co-author Dr. Penghua Wang, an immunologist at the University of Connecticut, said: "The findings could explain how mosquito viruses manage to persist for such a long time.

“The virus can manipulate the hosts’ skin microbiome to attract more mosquitoes to spread faster.”

Dr. Wang and his colleagues also tested a potential preventative by giving mice with dengue fever a type of vitamin A derivative, isotretinoin, known to increase the production of the skin’s antimicrobial peptide.

The isotretinoin-treated mice gave off less acetophenone, reducing their attractiveness to mosquitoes and potentially reducing the risk of infecting others with the virus.

Dr. Wang added: "The next step is to analyze more human patients with dengue and Zika to see if the skin odor-microbiome connection is generally true in real-world conditions, and to see if isotretinoin reduces acetophenone production in sick humans as well as it does in sick mice."