Viruses make people more attractive to mosquitoes, study finds

Scents from infected mice found to ‘stimulate a significant response in mosquito antennae’

Some viruses can change a body’s odour to be more attractive to mosquitoes, a new study has found.

Penghua Wang, an assistant professor of immunology at the University of Connecticut, noted in a piece for The Conversation that mosquitos are the deadliest animal in the world, causing more than a million deaths each year from diseases such as malaria, yellow fever, dengue fever, Zika, and chikungunya fever.

A mosquito that bites a person with a virus can transfer it to the next person the insect bites.

Factors such as body temperature, the carbon dioxide from a person’s breath and odour all play a role in how a mosquito chooses its next target.

Earlier studies have found that mice with malaria have their scents altered in a way that makes them more attractive to the insects.

Prof Wang wrote that the researchers “placed mice infected with the dengue or Zika virus, uninfected mice and mosquitoes in one of three arms of a glass chamber”.

“When we applied airflow through the mouse chambers to funnel their odors toward the mosquitoes, we found that more mosquitoes chose to fly toward the infected mice over the uninfected mice,” he said.

“After placing a filter in the glass chambers to prevent mice odors from reaching the mosquitoes, we found that the number of mosquitoes flying toward infected and uninfected mice were comparable,” Prof Wang added.

He said that three out of 20 gaseous chemical compounds from the scent radiated by the infected mice were found to “stimulate a significant response in mosquito antennae”.

One of the three compounds – acetophenone – attracted more mosquitoes than the control when applied to mice and the hands of human volunteers.

Infected mice produced 10 times more acetophenone than uninfected mice, according to the professor.

“Similarly, we found that the odors collected from the armpits of dengue fever patients contained more acetophenone than those from healthy people,” Prof Wang said. “When we applied the dengue fever patient odors on one hand of a volunteer and a healthy person’s odor on the other hand, mosquitoes were consistently more attracted to the hand with dengue fever odors.”

He said that the discoveries suggest that dengue and Zika viruses can rise the amount of acetophenone produced, making someone more attractive to the insects.

“When uninfected mosquitoes bite these attractive hosts, they may go on to bite other people and spread the virus even further,” Prof Wang wrote.

Acetophenone is a chemical used in perfumes as well as a metabolic byproduct that’s produced by skin bacteria and in both human and mouse intestines.

Prof Wang said that mosquitos “were significantly less attracted to infected mice with depleted skin bacteria,” possibly suggesting that “skin microbes are an essential source of acetophenone”.

The researchers found that the “rod-shaped bacteria” Bacillus was a “major acetophenone producer” which was discovered in larger than normal numbers on infected mice.

“This meant that the dengue and Zika viruses were able to change their host’s odor by altering the microbiome of the skin,” Prof Wang said.

The researcher said that vitamin A could be used to counteract the change in odour, noting that “vitamin A deficiency is common in developing countries”.

“This is especially the case in sub-Saharan Africa and Southeast Asia, where mosquito-transmitted viral diseases are prevalent,” he added. “Our next steps are to investigate whether dietary vitamin A or its derivatives could reduce mosquito attraction to people infected with Zika and dengue, and subsequently reduce mosquito-borne diseases in the long term.”