Mosquitoes are the deadliest animal in the world. More than 1 million deaths a year are attributed to mosquito-borne diseases, such as malaria, yellow fever, dengue, zika and chikungunya fever.
The way mosquitoes look for and feed on their hosts are important factors in the way a virus circulates in nature. Mosquitoes transmit diseases 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 who 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 some viruses can alter a person’s body odor to make them more attractive to mosquitoes, resulting in more bites that allow a virus to spread. .
Viruses change host odors to attract mosquitoes
Mosquitoes locate a potential host through different sensory signals, such as body temperature and carbon dioxide emitted by respiration.
Smells also play a role. Previous laboratory research has found that malaria-infected mice have changes in their odors that make them more attractive to mosquitoes.
With that in mind, my colleagues and I wondered if other mosquito-borne viruses, such as dengue and zika, can also change a person’s smell to make them more attractive to mosquitoes, and whether there is a way to prevent these changes.
To investigate, we placed mice infected with dengue or Zika virus, uninfected mice, and mosquitoes in one of the three arms of a glass chamber. When we applied a stream of air through the mouse chambers to channel their odors into the mosquitoes, we found that more mosquitoes chose to fly to the infected mice over the uninfected mice.
We discarded carbon dioxide as a reason why mosquitoes were attracted to infected mice, because while Zika-infected mice emitted less carbon dioxide than uninfected mice, dengue-infected mice did not change their diets. emission levels.
We also ruled out body temperature as a possible attractiveness factor when mosquitoes did not differentiate between mice with high or normal body temperatures.
We then evaluated the role of body odors in increasing the attraction of mosquitoes to infected mice.
After placing a filter in the glass chambers to prevent the smells of the mice 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 about the smells of infected mice that attracted mosquitoes to them.
To identify odor, we isolated 20 different gaseous chemical compounds from the odor emitted by infected mice. Of these, we found three to stimulate a significant response to 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 compared to 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 from healthy people.
When we applied the smells of the patient with dengue fever from one hand of a volunteer and the smell of a healthy person on the other, mosquitoes were constantly more attracted to the hand with the smells of dengue.
These findings imply that dengue and Zika viruses are able to increase the amount of acetophenone they produce and emit their hosts, 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 find out how viruses increased the amount of acetophenone that attracts mosquitoes that produce their hosts.
Acetophenone, in addition to being a chemical commonly used as a fragrance in perfumes, is also a metabolic byproduct commonly produced by certain bacteria that live on the skin and intestines of both humans and mice. So we wondered if it had anything to do with changes in the type of bacteria in the skin.
To test this idea, we removed the skin or intestinal bacteria from infected mice before exposing them to mosquitoes.
Although mosquitoes were even more attracted to mice infected with depleted intestinal 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 bacterial skin compositions of infected and uninfected mice, we identified that a common type of rod-shaped bacteria, Bacillus, was a large producer of acetophenone and had significantly increased the number of infected mice.
This meant that dengue and Zika viruses could change the smell of their host by altering the skin microbiome.
Reducing odors that attract mosquitoes
Finally, we wondered if there was a way to prevent this change in odors.
We found a potential option when we observed that infected mice had decreased the levels of an important anti-microbial molecule produced by skin cells, called RELMα. This suggested that dengue and Zika viruses suppressed the production of this molecule, making mice more vulnerable to infection.
Vitamin A and its related chemical compounds are known to strongly increase RELMα production. So we fed a vitamin A derivative to the infected mice for a few days and measured the amount of RELMα and Bacillus bacteria present in their skin, and then exposed 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 no more attracted to these infected and treated mice than uninfected mice.
Our next step is to replicate these results in people and ultimately apply what we learn to patients. Vitamin A deficiency is common in developing countries. This is especially the case in sub-Saharan Africa and Southeast Asia, where mosquito-borne viral diseases predominate.
Our next steps are to investigate whether dietary vitamin A or its derivatives could reduce the attraction of mosquitoes to people infected with Zika and dengue, and subsequently reduce long-term mosquito-borne diseases.
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.