Zika or dengue infections make you more appealing to mosquitoes

Humans and mice infected with Zika or dengue viruses secrete a chemical that makes them more appetising to mosquitoes, meaning they are more likely to be bitten again and further transmit these viruses. By pinpointing the chemical attractant, researchers were able to reduce the appealing scent with a common acne medication.

In tropical and subtropical regions of the globe, dengue infects around 400 million people annually and causes about 40,000 deaths. The Zika virus, which had large outbreaks in 2015 and 2016, infects hundreds of people each year and infection during pregnancy can lead to serious health problems in newborns. Both are spread by mosquitoes, which transmit the viruses through saliva when they feed on a host’s blood.

Gong Cheng at Tsinghua University in China and his colleagues knew that mosquito-borne pathogens like malaria can hijack our scent to make us more appetising, leading them to wonder if Zika and dengue could manipulate hosts in a similar way.

In their experiment, the researchers offered mosquitoes a choice of two meals: an uninfected mouse or a mouse infected with the dengue or Zika virus. They found that around twice as many mosquitoes opted to feed on infected mice compared with uninfected mice.

The researchers also analysed molecular compounds found on the skin of infected and uninfected mice and people, identifying several that were most common on Zika and dengue-positive hosts.

They then wiped those smelly compounds onto the backs of mice and onto human hands to see which scents were most appealing to mosquitoes. The most enticing smell was acetophenone, which was abundant on both humans and mice infected with either virus.

Mosquitoes rely heavily on scent to find a meal, picking up on subtle chemical signals that we can’t, says James Logan at the London School of Hygiene & Tropical Medicine, who wasn’t involved with the research. He notes that humans are covered in a complex mixture of more than two dozen smells, including many that make us more or less appetising to hungry insects.

There were earlier clues that diseases like malaria and covid-19 can affect a host’s microbiome, causing the bacteria that live in and on the skin to produce different amounts of select compounds. So while the researchers weren’t necessarily surprised to see this was the case with Zika and dengue as well, they were pleased to identify a single mosquito-enticing molecule, says Cheng.

Acetophenone, which is also found in some fruits and cheeses, is routinely produced by bacteria in human and mouse skin, but normally subdued by the skin’s natural antimicrobial peptides. Infected hosts seem to produce less of these peptides. By turning the infected mouse or person into a more attractive meal, the virus can then hop to new hosts more easily.

Once they identified the compound, the researchers wanted to see if they could suppress its production. Using clues from previous research, they decided to feed the mice a common acne medication called isotretinoin, which is known to ramp up the production of antimicrobial peptides. When they exposed mice treated with the drug to mosquitoes, the insects no longer showed a preference for the infected individuals.

Next, the researchers plan to take a closer look at the skin odours of people infected with Zika and dengue viruses. They are hopeful that the isotretinoin treatment could also deter mosquitoes from feeding on humans.

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