Dengue virus causes mosquito to bite victims more

The dengue virus appears to be able to manipulate the behavior of the mosquito Aedes aegypti, causing the insect to transmit the disease-causing agent more efficiently.

The mosquitoes that carry the virus are, at the same time, more avid in the search for animals whose blood they can suck and less skilled when trying to access that blood, which requires more contact with the victim’s skin on their part. These two factors can even triple the probability of transmission of dengue between people, says the international team of scientists that detected the phenomenon.

Coordinated by Julien Pompon, from the IRD (Institute for Research for Development), in France, the work has just been published in the American scientific journal PNAS.

“The data underscore the importance of mosquito behavior in disease transmission. Any virus that is not able to modify this behavior is unlikely to be able to be transmitted or emerge [ou seja, passar a infectar seres humanos]”, says Pompon to leaf.

In fact, examples of behavioral changes induced by the presence of microbes or parasites (such as worms) in the organism of their hosts have been discovered with increasing frequency by scientists. In the case of the dengue virus, however, the data in this regard were still contradictory.

Pompon and his colleagues tried to clarify what was going on by using high-resolution cameras calibrated to capture every step of a bite from the Aedes aegypti in the controlled environment of the laboratory. For this, they used a small acrylic box in which the mosquitoes were placed.

On top of the box was a fine mesh screen, through which the insects were able to insert their proboscis — the mouth projection that the insects use to penetrate the skin and suck the blood of their victims. Finally, an anesthetized mouse was lying on top of the screen. The rodent, after the bites, was examined for signs of transmission of the dengue virus (this in the case of the boxes where there were mosquitoes contaminated by the researchers; there were also insects from the control group, without viral infection).

After filming and analyzing the behavior of more than 50 of the Aedes aegypti in each of the groups, over periods lasting 30 minutes for each mosquito, the scientists first noticed that the insects infected with the virus approached the mice faster and more frequently than the uninfected ones.

Probably the most important point, however, is the fact that mosquitoes with the virus took longer to be able to suck blood and gave many unsuccessful bites — that is, without actually feeding on that blood. It turns out that this is exactly what the cause of dengue “wants” the animals to do.

This is because, in general, the virus comes out of the mosquitoes’ saliva and initially infects the victim’s skin cells. That is, the saliva of insects does not need to come into contact with the bloodstream for the person to catch the disease. In fact, the more times the proboscis of mosquitoes enters just a little bit into the skin, without reaching the blood, the better for the efficiency of transmission.

Scientists have also confirmed this experimentally. They let the insects bite the mice for just 20 seconds (which is not usually enough time for the animals to be able to feed on blood) and then shoo the mosquitoes away. Result: all Aedes were able to transmit the dengue virus to skin cells, even with “incomplete” bites.

According to the French researcher, it is possible that the virus is altering the functioning of the mosquito’s brain “or the olfactory tissues, which guide the insect’s mouth apparatus and flight when it seeks its victims”. Analyzing the activated and deactivated genes in the cells of the mosquito’s nervous system may provide more clues about what is happening and perhaps even inspire the creation of substances capable of blocking the action of the virus in Aedes.