Getting bitten by mosquitoes every day? You may have been caught by a virus in your body

  Why are some people more attracted to mosquitoes? In order to answer this question, scientists have worked hard for many years, but the answer has not been completely clear. However, in people infected with a type of arbovirus, the virus may use some tricks to make people more attractive to mosquitoes in order to spread among more people.
The conspiracy of creatures

  In nature, in order to reproduce, expand their populations and territories, some creatures often play some sinister tricks.
  In birds and insects, there is a phenomenon called “brood parasite”. Cuckoos do not raise their offspring by themselves, but lay their eggs in the nests of smaller birds that have a similar reproductive cycle to their own. They can lay an egg in 6 seconds, so the host can’t notice it at all. These eggs have thicker shells (resistance to falling and pecking) and look similar to the host’s eggs, hatching earlier. After the cuckoo chicks hatch, they will also squeeze other unhatched eggs out of the nest. The deceived small birds have to work hard to raise these young birds.
  In addition to raising children for other creatures, some insects are forced to grow up with the children of other insects and become their food. The mastermind of this process is a shrewd and vicious animal – the flat-headed mud bee. It will play against the American cockroach, which is much larger than itself, and take the opportunity to deliver some toxins into the American cockroach, making it a living “zombie”: incapacitated, it can only be obedient. The wasp then lays an egg inside the American cockroach and will find a good place to bury it. As the sun and the moon change, when the mud wasp larvae hatch, they can feast and grow healthily.
  However, in the cruel nature, the routines of some creatures to harm “people” will be hidden deeper, and they have truly achieved “killing people invisibly”. For example, a fungus called Myastheca infects female houseflies, manipulating them to climb to heights in their final stages before dying. After a female housefly dies, the fly mold releases compounds that attract males to mate. These young and fanatical males, all of whom eventually die from the infection, may have helped the fly mold spread further during their lifetime. For the fly mold, it was an easy victory.
manipulative flavivirus

  These stories are all far away from us human beings. However, in nature, the human body is also a walking energy treasure. Even with a strong immune system, it will attract coveted people. Recently, in a paper published in the journal Cell, scientists from the Shenzhen Bay Laboratory and Tsinghua University discovered that a type of virus controls gene expression in the human body to help itself spread, while bringing As a result, many people will die.
  These viruses that can manipulate people, Zika virus and dengue virus, will have a serious impact on people’s health and survival. They all belong to the genus Flavivirus, which infect people and cause similar symptoms, such as high fever, rash, bleeding, headache, and muscle and joint aches. The difference between the two is that the onset of dengue fever will be more acute, and if the patient develops severe dengue fever, he will soon die of respiratory failure and hemorrhagic shock.
  The Zika virus causes milder symptoms, similar to mild dengue fever, but it can infect the fetus through pregnant women and cause reproductive defects such as microcephaly (a severe head deformity). These fetuses experience rapid memory loss, physical incoordination, and language and hearing difficulties as they grow up.
  What connects people and these two terrifying viruses is a type of organism that humans are trying to kill, the carrier of the virus-Aedes mosquitoes (including Aedes aegypti, Aedes albopictus, etc.). Both viruses are arboviruses that are spread among vertebrates through the bite of the Aedes mosquito. They also break through the restriction that many viruses of the same family cannot reproduce in the human body, forming a human-mosquito-human transmission route. And this pathway can be maintained all the time because a necessary condition is met: the bloodthirsty female Aedes mosquitoes will take the initiative to bite people who carry the virus, and then pass the blood containing the virus to more people.

Electron microscope image of Zika virus

The baby on the left has microcephaly
More attractive to Aedes

  The initiative of Aedes mosquitoes is inseparable from the attraction of infected people to it, so why do infected people attract Aedes mosquitoes? The researchers believe there may be three reasons: carbon dioxide exhaled by an infected person, elevated body temperature, and chemicals released by the body. Through some experiments, they tested the attractiveness of healthy and diseased mice to Aedes aegypti. In one experiment, they prepared three connected small rooms (also called a three-cage experiment), and placed mosquitoes in the middle room, with two ends connected to the areas where the mice lived through pipes. The mice on one side were all healthy, while the mice on the other side were infected with Zika virus.
  Considering that 6 days after infection, the mice would begin to die from hemorrhagic fever, so the study was only conducted for 6 days. For the first few days, mice on both sides were equally attracted to Aedes—the same number of Aedes went from the middle to each room. But in 4 to 6 days, the situation changed. More Aedes — about 70 percent of the total — went to the room on the side of the infected mice. As a result, the mice became more attracted to mosquitoes after the infection worsened. The researchers also tested mice infected with dengue virus, with the same results.
  The three-cage experiment can test the difference in the attractiveness of healthy and virus-infected mice to mosquitoes.
  Human exhaled carbon dioxide has a strong attraction to mosquitoes. But in experiments, the researchers found that the carbon dioxide exhaled by the mice either decreased or remained unchanged after being infected with both viruses, so this factor could be ruled out. In addition, the mice’s increased body temperature did not change much in their attractiveness to mosquitoes. That leaves only the final factor in play—the chemicals the body releases.
  Other scientists have found that in malaria patients, Plasmodium infection can lead to an increase in some volatiles released from the patient’s skin, making it more likely to attract Anopheles mosquitoes. Similar changes may also be present in mice infected with Zika or dengue. So, they collected systemic volatiles released by healthy and infected mice on days 4 and 6 after infection, and tested them by gas chromatography, and found that these mice released a total of 422 species. Chemical material.

  Further testing found that the release of 12 and 11 chemicals, respectively, increased 1.5-fold or more in mice infected with Zika and dengue viruses. Ultimately, they pinpointed three compounds that triggered the mosquito’s olfactory neural response—acetophenone, decanal, and styrene—with acetophenone triggering the strongest neural activity. Through the three-cage experiment, they found that only acetophenone would make the ratio of the number of mosquitoes close to the infected mouse and normal mouse room to be 7:3, and only when the mass of acetophenone released by the mice reached 1 microgram or more, Mosquitoes will be motivated to search for the host from which the odor is released. In human infected people, the researchers also found that they released more acetophenone than normal people and were more likely to attract mosquitoes.
The mystery of acetophenone formation

  In fact, the human body cannot express the enzymes that make acetophenone, but the microbes in the human gut and skin can. The researchers found that the symbiotic flora on the skin of humans and mice played a key role in attracting Aedes mosquitoes. They analyzed those bacteria on the skin of infected mice and found that the numbers of four acetophenone-producing bacillus species increased significantly, while the numbers of non-acetophenone-producing lactobacilli decreased.
  It is a gene in the human body, Retnla, that drives these changes in the number of bacteria. In the skin of infected mice, the expression of this gene is reduced, and its production of the antibacterial protein RELMα is reduced, which also leads to insufficient RELMα to inhibit the proliferation of Bacillus, resulting in an imbalance of the skin flora. The study found that when mice were unable to express RELMα, it only took 3 days for Bacillus to rapidly proliferate as the main flora on the skin, producing a large amount of acetophenone. Zika virus and dengue virus can inhibit the expression of RELMα in the human body, and this process may be related to the effect of these two viruses on some human receptors.

Mice infected with Zika or Dengue virus (orange) express reduced levels of the antimicrobial protein RELMα compared to healthy mice (blue)

  Through such a tortuous process, the two viruses hide the changes they make to the infected person in the scent. This change is imperceptible to humans, but it will have a strong attraction to the Aedes mosquitoes that help spread the virus. People are inadvertently manipulated by these viruses and make sacrifices for the spread and growth of the virus.
  Fortunately, the researchers found that dietary supplementation of vitamin A can activate a signaling pathway in the human body, promote the formation of RELMα in the human body, achieve an antibacterial effect, and then prevent the further spread of the virus. After treatment with isotretinoin, a derivative of vitamin A, the number of Bacillus bacteria on the skin of virus-infected mice dropped significantly. And their attractiveness to mosquitoes dropped to the same level as uninfected mice. For humans, this may also be a good way to curb the spread of the virus.
  In addition to this special situation, in daily life, healthy people are more attracted to mosquitoes may also be related to the composition of bacteria on their skin. Several studies have confirmed that when the number of some bacteria on the skin changes, it also changes the odor emanating from the body, which in turn makes people more attractive to certain mosquitoes.
  Life is all about self-indulgence.

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