The smell of patients with dengue or Zika virus is irresistible to mosquitoes. A clever trick of these viruses, scientists discovered.
The mosquito season has been going on for a while now. Many people have sleepless nights with the endless sum. In the morning you have a couple of itchy buds as souvenirs. But it could be worse because mosquitoes (especially in tropical areas) also carry viral infections.
And these viruses are smarter than you think: by changing the scent of their host, they’ll get a lot more free ‘lifts’ for the next victim. For example, a research team led by Gong Cheng from China’s Tsinghua University in collaboration with other Chinese institutes and the University of Connecticut (USA) discovered.
abnormalities in the brain
Dengue and Zika viruses both belong to the so-called flavivirus family. Dengue causes dengue fever; you get fever, muscle aches and itching. In some cases, it can lead to heavy bleeding and death. Adults often do not become seriously ill from Zika, but if the mother is infected, it can lead to severe brain abnormalities in the unborn child.
Both flaviviruses rely on mosquitoes for their spread. So it would not be at all surprising if they found a way to lure those mosquitoes to them. The researchers wanted to find out.
They did this by infecting a group of mice with the dengue virus. Another group remained untouched. The team then released mosquitoes in the cages of both groups. What turned out? The diseased mice were stung much more often than the control group. The same was true for a group of mice infected with the Zika virus.
The same experiment was repeated, but with human dengue and Zika patients and a group of healthy individuals. Again, the mosquitoes appeared to have a preference for the infected individuals.
The next step was to find out the reason behind this preference. So the researchers took skin samples from sick and healthy people and mice and analyzed the odor molecules on them. In the analysis, they found that the dengue and Zika patients (and the mice) released a large amount of the molecule acetophenone.
Acetophenone – often also strongly present on ripe fruit and some cheeses – is made from Baccilus-bacteria. This bacterium lives on your skin, but is usually kept under control of the body’s own antibacterial substance RELMα.
The research team found that the two flaviviruses suppress the production of RELMα. As a result, Baccilus grows faster and therefore produces more acetophenone. And more acetophenone means more mosquitoes because they love this scent.
Now that it is known, according to the researchers, there is also hope. For example, they tested the vitamin A-like drug Isotretinoin, a remedy for teen pimples. This is known to help increase RELMα production. And in fact: the infected mice that got the drug released much less acetophenone. They were also stung much less compared to control mice.
The research team will now treat dengue and zika patients with isotretinoin to see if the effect is also visible there. In addition, according to the researchers, it is possible to genetically modify mosquitoes in such a way that they become much less sensitive to the odor molecule.
Molecular virologist Martijn van Hemert (LUMC) finds this research fascinating. “It’s wonderful to see how a relatively simple flavivirus manages to affect its own spread via mosquitoes through a complex and indirect mechanism.”
slow down the spread
But it is also not very surprising, says mosquito expert Bart Knols from Radboud University Nijmegen. “We have known for years that people infected with malaria parasites smell more attractive to mosquitoes. But it is new that it also applies to viral diseases. It is noteworthy that this can also be traced back to a single substance, acetophenone. The question is how this knowledge can be used to fight diseases more effectively. “
Van Hemert has an idea for this. “With this, one could find ways to inhibit the mosquito’s spread of the virus through interventions (such as with the isotretinoin mentioned by the researchers, ed.) In the infected patient and his surroundings. But in the end, it may still be the case that the virus will once again find a way around this strategy. “
Sources: Cell, Cell Press, University of Connecticut