A recurring theme that creeps into our collective consciousness to fuel our irrational fears: Is HIV transmitted by mosquito bites?
It is impossible to become infected with the Human Immunodeficiency Virus (HIV) through a mosquito bite. However, on certain online platforms and social networks, the topic is still regularly discussed. Although knowledge about the transmission of this AIDS virus that causes AIDS is now well established among scientists, it is not always known to everyone.
Unlike the Zika virus or malaria parasites, HIV cannot be transmitted to humans by mosquitoes. Firstly, it is not so easy for a virus to spread through mosquitoes, whether HIV or not. You may think that if an insect ingests a virus from an infected person during a blood meal, it can pass it on to a healthy person at the next meal. In fact, it is a little more complicated than that.
Transmission of viruses through Mosquitos not so easy
In fact, once a virus has been ingested during a blood meal, it must resist the hostile environment in the mosquito’s intestines (acidity, digestive enzymes…). It must then reach the cells of the intestinal wall and find an anchor point to penetrate and multiply in the cells, which is not without problems.
After the viral load (i.e. the amount of virus) has increased, the virus must be released into the mosquito’s body, infecting the salivary glands and multiplying again. And only there, with the anticoagulant saliva stored in the cavities of the salivary glands (lumens), could it be injected into a new host during the next blood meal of the mosquito.
Each virus has its own specific requirements
Moreover, not all viruses are the same: some viruses penetrate and multiply more easily into cells than others. This is the case with the Zika or Chikungunya viruses. Hepatitis C virus and HIV, on the other hand, are much more “sophisticated”: they only infect some very specific cell types that are not found in all species.
In humans, the targets of HIV are mainly T-helper T cells, monocytes, macrophages, and dendritic cells. These cells are essential for the proper functioning of the immune system. The virus is able to recognize and bind to “anchors” or markers expressed on the surface of these cells, known as CD4 receptors. In this way, the virus multiplies and spreads throughout the body.
Mosquito cells, however, do not have these anchors on their surface. Even if a mosquito were to feed on the blood of an HIV-infected person, the blood could not enter the cells. Even if this were the case, it could not reproduce if there were no cellular factors essential for reproduction. Therefore, HIV cannot infect the mosquito and be “actively” transmitted to a person.
The HIV virus is unstable and does not survive for long.
Can the mosquito’s trunk be a transmission vector when the insect that has just fed on the blood of an HIV-positive person immediately bites another person? This is also impossible for two reasons. The mosquito’s trunk actually contains two different channels: one for taking blood and a smaller channel for injecting saliva.
Since the circulation is unidirectional, a mosquito can only transmit the virus if it is infected and the pathogen is found in its saliva after it has reproduced. Since HIV, as already mentioned, cannot reproduce in mosquito cells, this possibility can be excluded. On the other hand, it is an unstable virus that does not survive for long outside the cells in which it multiplies or in body fluids.
Finally, it can be added that even if a mosquito with a proboscis covered with contaminated blood bites a person who is not HIV-positive immediately, they would not be able to transmit the virus to him. The viral load contained in the few infected lymphocytes that would be transmitted to this individual would indeed be too low.
In a publication published over 20 years ago, it was shown that it would take ten million bites from infected mosquitoes for the viral load passively transmitted through the trunk to be sufficient to infect a person