Mosquitoes – what can I say, we hate them. They make annoying noises, are always buzzing around in front of your nose and their bites are itchy. And to make matters worse, they also transmit diseases. By the way, this circumstance is very convenient for viruses. They can be easily carried and spread from place to place via the blood of their infected hosts. But why are some people bitten by mosquitoes more often than others? One explanation is the smell emitted by the potential stab victims. And some bodies smell more enticing than others. This realization is not new. Plants also use this method to attract pollinators.
Viruses change the body odor of their hosts
Viruses also use this clever circumstance to spread themselves. Researchers at Tsinghua University in Beijing have investigated this using the Zika and dengue viruses as examples. They have now published their study results in Cell magazine.
The research team locked a group of infected mice and a group of healthy mice in a box with hungry mosquitoes and observed who got bitten more often. Between 60 and 75 percent of the mosquitoes were attracted to the infected mice. The researchers found that these mice produce more acetophenone than the healthy animals.
Acetophenone is an aromatic organic chemical compound that is also found in many fruits and some types of cheese. It is present in the infected in a particularly high concentration and makes it smell very delicious for mosquitoes.
Regulatory mechanisms of the skin undermined
Acetophenone is naturally formed on the skin. Normally, the key protein RELMa regulates the composition of the skin’s microbiome and keeps acetophenone-producing bacteria in check. However, the dengue and Zika viruses suppress RELMa. That is, the acetophenone-producing bacteria multiply excessively, and sick people or animals suddenly smell very attractive to mosquitoes.
The mosquitoes and viruses enter into a sophisticated symbiosis. Zika and dengue viruses rely on mosquitoes to survive. The disease is mainly transmitted by diurnal mosquitoes of the genus Aedes, especially Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito). If a healthy mosquito bites an infected host, it carries the virus on. Mosquitoes, in turn, rely on their sense of smell to guide their survival. A perfect match – but also a great threat.
Dengue fever: One of the top ten threats to world health
Almost half the world’s population lives in areas at high risk of dengue fever. It occurs in the tropical and subtropical areas of Asia, Africa and Latin America. The WHO ranks dengue fever among the ten greatest threats to world health, as the distribution area is expanding and infections are increasing. There are four subtypes of the virus. So you can get infected four times. Once infected, there is lifelong immunity. But the infections are by no means harmless, because each subsequent infection also increases the risk of a serious course of the disease.
Dengue viruses damage the blood-forming system. In dengue fever, there is a reduction in blood cells, especially thrombocytes, which are important for blood clotting. In the first form, classic dengue fever, sufferers develop flu-like symptoms and a skin rash. The fever usually heals without consequences. The second form is dengue hemorrhagic fever (DHF), which in extreme cases can lead to dengue shock syndrome (DSS). Left untreated, DHF and DSS are often fatal. Children in particular are at risk.
Although there is a dengue vaccine Dengvaxia, it is only recommended with reservations because it can make the disease worse. In 2017, the vaccination campaign in the Philippines had to be stopped because of serious complications and deaths. A new vaccine is currently in a phase III trial and is being tested.
Find other ways to counter mosquito-friendly odor
So, to help stem the spread of dengue in another way, it would be beneficial if carriers of the virus didn’t smell so tempting to mosquitoes. So how can acetophenone production be suppressed?
After Gong Cheng’s team had combed through the existing literature on the key protein RELMa, the researchers came across the active ingredient isotretinoin. So they fed infected mice isotretinoin and put them back in a box with mosquitoes. The results were encouraging. The infected mice were not bitten more often than the healthy mice.
“Dietary administration of isotretinoin to flavivirus-infected animals reduced acetophenone volatilization by remodeling the resident commensal bacteria (mostly living in harmless symbiosis with the host) on the host’s skin,” says Cheng. The researchers’ next step is to test the effect of isotretinoin treatment in humans to reduce acetophenone-induced mosquito activity. It might well be an approach to reducing the spread of Dengue and Zika.
Serious side effects: follow-up research needed
Of course, this has yet to be studied extensively because while isotretinoin is a drug that has been used to treat severe acne for many years, it is also a prescription drug with a long list of potentially serious side effects. Especially women of childbearing age should only take it if they use contraception at the same time, as there is an extremely high risk that the drug will cause severe birth defects in the unborn child. In addition, the isotretinoin treatment is temporary, but mosquitoes must be permanently prevented from biting people. So a bit of research needs to be done in the country before dengue fever can be prevented from spreading in this way.
