The smell of patients with the dengue or Zika virus is irresistible to mosquitoes. A clever trick of those viruses, scientists discovered.
Mosquito season has been underway for a while now. Many a person has sleepless nights of that endless buzzing. In the morning you then have a few itchy bumps as a souvenir. But it could be worse, because mosquitoes (especially in tropical areas) also carry virus infections.
And those viruses are smarter than you think: by changing their host’s scent, they get a lot more free ‘lifts’ to the next victim. So discovered a research team led by Gong Cheng of China’s Tsinghua University in collaboration with other Chinese institutes and the University of Connecticut (USA).
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The dengue and Zika virus both belong to the so-called flavivirus family. Dengue causes dengue fever† you get a fever, muscle aches and itching. In some cases, it can lead to heavy bleeding and death. From Zika adults often do not become seriously ill, but if the mother is infected, it can lead to severe brain abnormalities in the unborn child.
Both flaviviruses depend on mosquitoes for their spread. So it wouldn’t be surprising at all 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 into the cages of both groups. What turned out? The sick 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.
Odor molecules
The next step was to find out the reason behind that preference. So the researchers took skin samples from sick and healthy humans and mice and analyzed the odor molecules on them. In the analysis, they found that the dengue and Zika patients (and mice) released a large amount of the molecule acetofenon.
Acetophenone – often also strongly present on ripe fruit and some cheeses – is made by the Baccilus-bacteria. This bacteria lives on your skin, but is normally kept under control by 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 fragrance.
Now that this is known, there is also hope, according to the researchers. This is how they tested the vitamin A-like substance Isotretinoïne, a remedy for pimples. This is known to help ramp up RELMα production. And indeed: the infected mice that were given the drug released much less acetophenone. They were also stung much less compared to control mice.
Fighting the diseases?
The research team now wants to treat dengue and Zika patients with isotretinoin to see whether the effect is visible there too. Furthermore, according to the scientists, 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 is wonderful to see how a relatively simple flavivirus manages to influence its own spread via mosquitoes through a complex and indirect mechanism.”
slow down spread
But it is also not very surprising, says mosquito expert Bart Knols of Radboud University Nijmegen. “We have known for years that people are infected with malaria parasites smell more attractive for mosquitoes. But the fact that this also applies to viral diseases is new. It is remarkable that this can also be traced back to a single substance, acetophenone. The question remains as to how this knowledge can be used to combat the diseases more effectively.”
Van Hemert does have an idea about this. “With this you could find ways to inhibit the spread of the virus by the mosquito through interventions (such as with the isotretinoin mentioned by the researchers, ed.) in the infected patient and his environment. However, it may still be the case that the virus will find a way to circumvent this strategy again.”
Sources: Cell, Cell Press, University of Connecticut
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