More attractive to mosquitoes: Dengue viruses change the smell of their hosts

Mosquitoes – what can I say, we hate them. They make annoying noises, they always buzz in front of your nose and their bites itch. And as if that weren’t enough, they also transmit diseases. By the way, this circumstance is very convenient for viruses. They are easily transported and spread from one place to another through 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 potential stab victims. And some bodies smell more tempting 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. Researchers at Tsinghua University in Beijing have studied this using the Zika and dengue viruses as examples. They have now published the study results in the journal Cell.

The research team locked a group of infected mice and a group of healthy mice in a box with hungry mosquitoes and observed who was bitten most often. Between 60 and 75 percent of mosquitoes were attracted to infected mice. The researchers found that these mice produced more acetophenone than 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 the smell very delicious for mosquitoes.

Weakened skin regulation mechanisms

Acetophenone forms naturally 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.

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, in particular Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito). If a healthy mosquito bites an infected host, it transmits the virus. 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

Nearly half of the world’s population lives in areas at high risk for dengue fever. It is found in tropical and subtropical areas of Asia, Africa and Latin America. WHO ranks dengue fever among the ten greatest threats to world health, as the distribution area is expanding and infections are on the rise. There are four subtypes of viruses. So you can get infected four times. Once infected, there is lifelong immunity. But infections are by no means harmless, because each subsequent infection also increases the risk of a severe 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, the classic dengue fever, sufferers develop flu-like symptoms and a rash. 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 Dengvaxia dengue vaccine, it is only recommended with reservations as it can worsen the disease. In 2017, the vaccination campaign in the Philippines had to be stopped due to serious complications and deaths. A new vaccine is currently in a phase III trial and is being tested.

Find other ways to counteract the mosquito-friendly odor

So to help stem the spread of dengue in another way, it would help if the carriers of the virus didn’t smell as tempting to mosquitoes. So how can acetophenone production be suppressed?

After Gong Cheng’s team reviewed the existing literature on the key RELMa protein, the researchers came across the active ingredient isotretinoin. Then they fed the infected mice with isotretinoin and put them back in a box with the mosquitoes. The results were encouraging. Infected mice were not bitten as often as healthy mice.

“Dietary administration of isotretinoin to flavivirus-infected animals reduced acetophenone volatilization by remodeling resident commensal bacteria (which mainly live 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 could very well be an approach to reduce the spread of Dengue and Zika.

Serious Side Effects: Follow-up research is needed

Of course, this has yet to be thoroughly researched 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 of the drug causing severe birth defects in the unborn child. Also, isotretinoin treatment is temporary, but mosquitoes need to be permanently prevented from biting people. So a little research needs to be done in the country before dengue fever can be prevented from spreading in this way.

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