These microbes could make you more attractive to mosquitoes, mouse study finds

Mosquitoes are the deadliest animal in the world. More than one million deaths a year are attributed to mosquito-borne diseases, including malaria, yellow fever, dengue fever, Zika and chikungunya fever.

The way mosquitoes seek out and feed on their hosts is an important factor in how a virus circulates in nature. Mosquitoes spread disease by acting as carriers of viruses and other pathogens: a mosquito that bites a person infected with a virus can acquire the virus and transmit it to the next person it bites.

For immunologists and infectious disease researchers like me, a better understanding of how a virus interacts with a host can offer new strategies for preventing and treating mosquito-borne diseases.

In our recently published study, my colleagues and I found that certain viruses can alter a person’s body odor to be more attractive to mosquitoes, leading to more bites that allow the virus to spread.

Viruses modify host odors to attract mosquitoes

Mosquitoes locate a potential host through different sensory signals, such as your body temperature and the carbon dioxide emitted by your breath.

Smells also play a role. Previous laboratory research has shown that mice infected with malaria have changes in their odors that make them more attractive to mosquitoes.

With this in mind, my colleagues and I wondered if other mosquito-borne viruses, such as dengue and Zika, could also alter a person’s scent to make them more attractive to mosquitoes, and s there was a way to prevent these changes.

To study this, we placed mice infected with dengue or Zika virus, uninfected mice, and mosquitoes in one of three arms of a glass chamber. When we applied airflow through the mice’s chambers to channel their odors towards the mosquitoes, we found that more mosquitoes chose to fly towards the infected mice rather than the uninfected mice.

We ruled out carbon dioxide as the reason mosquitoes were attracted to infected mice because while Zika-infected mice emitted less carbon dioxide than uninfected mice, dengue-infected mice did not alter the emission levels.

Similarly, we excluded body temperature as a potential attractant when mosquitoes did not discriminate between mice with elevated or normal body temperature.

Next, we assessed the role of body odor in the increased attraction of mosquitoes to infected mice.

After placing a filter in the glass chambers to prevent mouse odors from reaching the mosquitoes, we found that the number of mosquitoes flying towards infected and uninfected mice was comparable.

This suggests that there was something in the smells of the infected mice that attracted mosquitoes to them.

To identify the odor, we isolated 20 different gaseous chemical compounds from the odor emitted by the infected mice. Of these, we have found three to stimulate a significant response in mosquito antennae.

When we applied these three compounds to the skin of healthy mice and to the hands of human volunteers, only one, acetophenone, attracted more mosquitoes than the control. We found that infected mice produced 10 times more acetophenone than uninfected mice.

Similarly, we found that odors collected from the armpits of dengue patients contained more acetophenone than those of healthy people.

When we applied the smells of dengue patients on the one hand to a volunteer and the smell of a healthy person on the other hand, mosquitoes were consistently more attracted to the hand with dengue smells.

These results imply that dengue and Zika viruses are able to increase the amount of acetophenone their hosts produce and emit, making them even more attractive to mosquitoes. When uninfected mosquitoes bite these attractive hosts, they can bite other people and spread the virus even further.

How Viruses Increase Acetophenone Production

Next, we wanted to understand how viruses increased the amount of mosquito-attracting acetophenone produced by their hosts.

Acetophenone, in addition to being a chemical commonly used as a fragrance in perfumes, is also a metabolic by-product commonly produced by certain bacteria living on the skin and in the intestines of people and mice. So we wondered if it had something to do with changes in the type of bacteria present on the skin.

To test this idea, we removed skin or gut bacteria from infected mice before exposing them to mosquitoes.

While mosquitoes were even more attracted to mice infected with depleted gut bacteria compared to uninfected mice, they were significantly less attracted to mice infected with depleted skin bacteria.

These results suggest that skin microbes are an essential source of acetophenone.

When we compared the skin bacterial compositions of infected and uninfected mice, we identified that a common type of rod-shaped bacteria, Bacilluswas a major producer of acetophenone and significantly increased the number of infected mice.

This meant that dengue and Zika viruses were able to alter the smell of their host by altering the skin microbiome.

Reduce odors attracting mosquitoes

Finally, we wondered if there was a way to prevent this change in smells.

We found a potential option when we observed that infected mice showed decreased levels of an important microbial-fighting molecule produced by skin cells, called RELMα. This suggested that dengue and Zika viruses suppress production of this molecule, making mice more susceptible to infection.

Vitamin A and its related chemicals are known to strongly stimulate the production of RELMα. We therefore gave a vitamin A derivative to infected mice for a few days and measured the amount of RELMα and Bacillus bacteria on their skin, then expose them to mosquitoes.

We found that infected mice treated with the vitamin A derivative were able to restore their RELMα levels to those of uninfected mice, as well as reduce the amount of Bacillus bacteria on their skin. Mosquitoes were also not attracted to these treated infected mice more than to uninfected mice.

Our next step is to replicate these results in people and eventually apply what we learn to patients. Vitamin A deficiency is common in developing countries. This is particularly the case in sub-Saharan Africa and Southeast Asia, where mosquito-borne viral diseases are prevalent.

Our next steps are to determine whether dietary vitamin A or its derivatives could reduce mosquito attraction for people infected with Zika and dengue, and subsequently reduce mosquito-borne diseases in the long term.

Penghua Wang, assistant professor of immunology, University of Connecticut.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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