These Microbes Could Make You More Attractive to Mosquitoes

Mosquitoes are the world's most lethal animal. Mosquito-borne infections cause about one million fatalities each year, including malaria, yellow fever, dengue fever, Zika, and chikungunya fever.

The manner in which mosquitoes seek out and feed on their victims influences how a virus spreads in nature. Mosquitoes spread diseases by serving as carriers of viruses and other pathogens. For example, if a mosquito bites a person afflicted with a virus, the mosquito can pick up the infection and pass it on to the next person it bites.

A deeper knowledge of how a virus interacts with a host might lead to new techniques for preventing and treating mosquito-borne infections, according to immunologists and infectious disease specialists like myself.

My colleagues and I discovered that some viruses may change a person's body odor to make them more appealing to mosquitoes, resulting in more bites that allow a virus to propagate. 

Viruses change host odors to attract mosquitoes

Mosquitoes detect prospective hosts through a variety of sensory signals, including your body temperature and the carbon dioxide generated by your breath.

Odors have a part as well. Previous laboratory study has discovered that mice afflicted with malaria have fragrance modifications that make them more appealing to mosquitos.

With this in mind, my colleagues and I wondered if other mosquito-borne diseases, such as dengue and Zika, may alter a person's fragrance to make them more appealing to mosquitos, and if there is a strategy to avoid these changes.

To examine this, we placed infected and uninfected mice, as well as mosquitoes, in one of three arms of a glass container. When we used airflow through the mouse rooms to direct their smells toward the mosquitoes, we discovered that the infected mice attracted more mosquitoes than the uninfected mice.

We ruled out carbon dioxide as a factor in mosquito attraction to infected mice because, whereas Zika-infected mice released less carbon dioxide than uninfected mice, dengue-infected mice emitted the same amount.

Similarly, when mosquitoes did not distinguish between mice with increased or normal body temperatures, we ruled out body temperature as a potential appealing feature.

The researchers then investigated the significance of body scents in mosquitoes' enhanced attraction to sick mice.

We discovered that the number of mosquitos flying toward infected and uninfected mice was equivalent after inserting a filter in the glass chambers to prevent mouse scents from reaching the mosquitoes.

This implies that something in the scents of the diseased mice lured the mosquitos to them.

We separated 20 distinct gaseous chemical components from the aroma generated by the afflicted mice to identify the odor. Three of them elicited a strong reaction in mosquito antennae.

Only acetophenone attracted more mosquitoes than the other two chemicals when applied to the skin of healthy mice and the hands of human volunteers. Infected mice generated ten times as much acetophenone as uninfected mice.

Similarly, we discovered that smells obtained from dengue fever patients' armpits included more acetophenone than those gathered from healthy persons.

Mosquitoes were continuously more attracted to the hand with dengue fever scents when we placed dengue fever patient odors on one hand of a volunteer and a healthy person's odor on the other.

These findings suggest that the dengue and Zika viruses can increase the quantity of acetophenone produced and released by their hosts, making them even more appealing to mosquitoes. Uninfected mosquitos that bite these attractive hosts may then bite other individuals, spreading the infection even farther.

How viruses increase acetophenone production

The next step was to figure out how viruses increased the quantity of mosquito-attracting acetophenone produced by their hosts.

Acetophenone is a metabolic byproduct generated by specific bacteria residing on the skin and in the intestines of both humans and mice. So we wondered whether it had anything to do with changes in the sort of bacteria on the skin.

To put this theory to the test, we eliminated either the skin or intestinal bacteria from infected mice before exposing them to mosquitoes.

While mosquitos were still attracted to infected mice with low intestinal bacteria relative to uninfected mice, they were much less attracted to infected animals with depleted cutaneous bacteria.

These findings imply that skin microorganisms are an important source of acetophenone.

When we analyzed the skin bacteria compositions of infected and uninfected mice, we discovered that Bacillus, a common form of rod-shaped bacteria, was a major acetophenone producer and had much higher levels on infected animals.

This suggested that the dengue and Zika viruses may modify the odor of their hosts by changing the skin microbiota.

Reducing mosquito-attracting odors

Finally, we questioned whether there was a method to avoid this odor change.

We discovered one possible explanation when we discovered that infected mice had lower amounts of RELM, a key microbe-fighting protein generated by skin cells. This showed that the dengue and Zika viruses inhibited molecule creation, making the mice more susceptible to infection.

Vitamin A and its associated chemical compounds have been shown to significantly increase RELM synthesis. So we fed infected mice a vitamin A derivative for a few days, evaluated the amount of RELM and Bacillus bacteria on their skin, and then exposed them to mosquitoes.

We discovered that infected animals treated with the vitamin A derivative were able to restore their RELM levels to those of uninfected mice while also reducing the number of Bacillus bacteria on their skin. Mosquitoes were no more attracted to these treated, sick mice than to uninfected mice.

Our next step will be to replicate these findings in humans and then apply what we've learned to patients. Vitamin A insufficiency is widespread in underdeveloped nations. This is especially true in Sub-Saharan Africa and Southeast Asia, where mosquito-borne viral infections are common.

The next stage will be to see if dietary vitamin A or its derivatives may diminish mosquito attractiveness to persons afflicted with Zika and dengue, and hence minimize mosquito-borne infections in the long run.

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.