Mosquitoes are attracted to people whose fragrance has been altered by viruses
There is no more lethal animal than a mosquito. Malaria, yellow fever, dengue fever, Zika, and chikungunya are just a few of the mosquito-borne illnesses that kill more than a million people annually.
How mosquitoes locate and feed on their victims is crucial to the spread of a virus in the wild. Mosquitoes are important vectors for the transmission of illness because they pick up and transmit viruses and other infections through their bites.
A deeper knowledge of virus-host interactions, such as my own, may lead to novel approaches to preventing and treating mosquito-borne illnesses. Recently, my colleagues and I released research showing that some viruses may cause a person’s body odour to become more enticing to mosquitoes, thereby increasing the likelihood that the person would be bitten and spreading the virus.
Because mosquitoes are attracted to the altered host odours, viruses can spread from person to person.
Mosquitoes use a variety of indicators, including your body temperature and exhaled carbon dioxide, to seek a possible host. As a side note, smells are also important. Malaria-infected mice have altered odours that make them more appealing to mosquitoes, according to previous laboratory studies. This got my coworkers and I thinking about whether or if other mosquito-borne illnesses, like dengue and Zika, may alter a person’s fragrance in a similar manner, and whether or not there is any way to avoid this.
We used a glass box with three arms, placing infected mice, uninfected mice, and mosquitoes in each arm to see what would happen. We discovered that more mosquitoes flew toward the infected mice than the uninfected mice when airflow was supplied through the mouse chambers to funnel their scents toward the insects.
While Zika-infected mice released less carbon dioxide than uninfected mice, dengue-infected animals released no different amounts of carbon dioxide than uninfected mice, so we can rule out carbon dioxide as a reason why mosquitoes were drawn to the infected mice. Again, since mosquitoes did not prefer one type of mouse over another with regards to body temperature, we can rule out that element as a potential attractant.
Then, we determined how much more mosquitoes were drawn to sick mice based on their smell. It was discovered that the quantity of mosquitoes flying toward infected and uninfected mice was similar when a filter was placed in the glass chambers to prevent the mosquitoes from smelling the mice. This shows that the mosquitoes were attracted to the sick mice by their scent.
We were able to extract 20 distinct gaseous chemical compounds from the odour given off by the diseased mice, which helped us to determine what was causing the odour. We discovered that three of these caused a notable reaction in mosquito antennae. Only one of the three chemicals, acetophenone, attracted more mosquitoes than the control when applied to the skin of healthy mice and the hands of human volunteers. Mice with the infection showed a tenfold increase in acetophenone production compared to control mice.
Similarly, we observed that dengue fever patients’ armpit odour samples had a higher concentration of acetophenone than healthy controls. Mosquitoes were constantly drawn more to the hand of a volunteer that had dengue disease patient smells applied to it than to the hand of a healthy person.
These results suggest that the dengue and Zika viruses can cause their hosts to manufacture and exhale more acetophenone, boosting their attractiveness to mosquitoes. These hosts are attracted to mosquitoes, which may then attack those who are uninfected.
How acetophenone synthesis is boosted by viruses
Next, we sought to figure out how viruses were raising the quantity of mosquito-attracting acetophenone their hosts make. Acetophenone is a chemical used in fragrances, but it is also a result of the metabolism of bacteria that live on the skin and in the intestines of humans and mice. Because of this, we pondered whether or not this may be related to shifts in the composition of skin bacteria.
To put this theory to the test, we isolated germs from the skin or the intestines of sick mice and then subjected them to mosquito bites. Mosquitoes were still attracted more to infected mice with reduced intestinal bacteria compared to uninfected mice, but they were far less attracted to infected animals with reduced cutaneous bacteria. These data show that skin microorganisms are a crucial source of acetophenone.
When we analysed the skin bacteria compositions of infected and uninfected mice, we observed that a common form of rod-shaped bacteria, Bacillus, was a key acetophenone producer and had dramatically higher numbers on infected animals. This suggested that the dengue and Zika viruses were able to affect their host’s odour by altering the microbiome of the skin.
Smells that attract mosquitoes can be mitigated.
Finally, we considered the possibility of finding a means to forestall the onset of an unpleasant aroma.
We discovered one possibility after discovering that infected mice exhibited lower amounts of RELM, a key protein generated by skin cells that inhibits the growth of microbes. This showed that the dengue and Zika viruses reduced synthesis of this chemical, making the mice more sensitive to infection.
Intense stimulation of RELM synthesis has been linked to vitamin A and its chemical derivatives. Our team exposed infected mice to mosquitoes after feeding them a vitamin A derivative over the course of several days in order to quantify the levels of RELM and Bacillus bacteria on their skin. We discovered that infected animals given the vitamin A derivative had their RELM levels restored to those of uninfected mice and the number of Bacillus bacteria on their skin decreased. These treated infected mice did not attract any more mosquitoes than untreated mice.
Our next step will be to test these hypotheses in human subjects and perhaps put this knowledge to use in treating patients. Vitamin A insufficiency is widespread in underdeveloped nations. This is notably the case in sub-Saharan Africa and Southeast Asia, where mosquito-transmitted viral infections are endemic. Our next step is to examine whether or not consuming vitamin A or its derivatives might lessen the likelihood that infected mosquitoes will be drawn to a human host, hence decreasing the prevalence of mosquito-borne illnesses like Zika and dengue.