Wed. Aug 10th, 2022

Mosquitoes can be choosy about who they hang out with, swarming around some people while totally avoiding others.

And it turns out some viral infections can make you especially attractive to the tiny blood suckers.

A new study has found that getting infected with a virus like dengue or Zika can make you smell delicious to mosquitoes, the flying carriers of these infections.

Once infected, mice and humans secrete a compound that’s like catnip to mozzies, leading them to bite their hosts, suck their blood and carry the virus to their next victim, according to research published today in the journal Cell.

Mosquitoes need to actively seek and feed on [an infected] host to acquire infectious viral particles, “said lead author Gong Cheng, an immunologist at Tsinghua University in Beijing.

“The viruses subsequently establish an infection in the mosquitoes, thereby enabling them to transmit viruses to naive hosts through blood feeding.”

Deadly disease vectors

It’s no secret that mosquitoes are a bit of a nuisance, but they can also be dangerous disease carriers, particularly in tropical regions.

Among the mosquitoes spread infections are flaviviruses – a family that includes dengue, Zika, Japanese encephalitis, and yellow fever.

Dengue alone affects over 50 million people each year, leading to roughly 20,000 deaths.

These viruses need to be continuously taken up by mosquitoes and human hosts in order to spread and survive, Professor Cheng said.

Mosquitoes rely on their sense of smell to find their next meal, and previous studies have found that malaria infections – another mosquito-borne disease caused by a parasite – can change people’s scent, making them more attractive to mozzies.

Indian woman feeding man in hospital bed
Dengue fever is a moquito-borne disease that affects millions of people worldwide each year. (Getty Images: Allison Joyce / Stringer)

Professor Cheng and his team wondered whether dengue and Zika infections also produced a mosquito-drawing odor.

To the find out, the researchers placed 60 Aedes aegypti mosquitoes into a special enclosure.

Three Zika-infected mice were placed inside a chamber at one end of the enclosure, while three healthy mice were placed inside another chamber on the opposite side.

After six days, the researchers counted how many mozzies ended up in each chamber.

They found that about 70 percent had buzzed their way into the infected mouse chamber.

When the team tried out the same experiment with dengue-infected mice, the mosquitoes were also more attracted to them than their healthy counterparts, indicating there was something appealing about the virus-laden mice.

A chemical cocktail

Next, the team wanted to find out what chemicals were making the sick mice so mouth watering to the mosquitoes.

They placed the healthy and infected mice into separate glass chambers that were each connected to a filter.

After blasting the mice with air for eight hours to get a whiff of their odor, Dr Cheng and his team analyzed the compounds each filter had collected.

They found abnormally high levels of 20 compounds among the Zika and dengue-infected mice.

The team then exposed the mosquitoes to each compound and measured the electrical activity in their antennae to see which one they responded to the most.

Asian scientists in lab coats standing around a clear plastic box
Gong Cheng (pictured right) and his team found mosquitoes were more attracted to the smell of sick mice. (Supplied: Xuan Guo)

Three of these compounds – acetophenone, decanal and styrene – triggered the strongest responses in the mosquitoes’ antennae.

Taking things a step further, the researchers dabbed a bit of each chemical onto the mice to see which one was the top mosquito magnet.

Of all the compounds, the mosquitoes went wildest for acetophenone, a compound naturally found in apples, cheese and beef.

But the team wanted to see whether the presence of this delicious-smelling chemical was also present in humans with dengue fever.

So, they took swabs from the armpits of 16 dengue patients and 16 healthy people and rubbed them onto pieces of filter paper.

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