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Sunday, February 15, 2015

Why mosquitoes cannot cause HIV/AIDS

Probably the most commonly asked question about AIDS is whether the virus spreads through mosquitoes other blood sucking insects and the fear that brought up this question is justified as today, available statistics have shown that estimated 1.6 million people die of HIV and AIDS.

Fortunately, the answer is no. However, because so much have already been written about this subject, it is worth looking at the question in some detail. In theory, there are two ways in which a mosquito or other insects could transmit HIV, the virus that causes AIDS; biologically or mechanically.

Malaria is biologically transmitted when the parasite enters the mosquito, thrives and then makes its way into the insect’s salivary glands, from which it is injected into another person. This sequence of event is unlikely for HIV because the virus appears to replicate in a narrow of mammalian cells.

The second hypothesis is mechanical transmission, with the virus spreading on the insect’s mouth part which might become contaminated, with the blood containing HIV. If a mosquito bit a person infected with the virus and was then disturbed, so that it interrupted its feeding, the insect will then fly off to bite another person. According to this theory, the insect would then operate like a very tiny contaminated needle. The evidence against mechanical transmission comes from several sources.

First, the age and sex distribution of people infected with HIV in Africa is typically of a sexually transmitted disease. If insects spread HIV, there should be just as much, possibly more, infections among young children and older people between 20 and 40 years old. Thus for example, malaria is common among infants and young children in these areas. Several studies among families of AIDS patients in Africa show that people who live in the same household as AIDS patients don’t usually have the virus. The only exception to this was if they were the sexual partner (spouse) or child of the AIDS patient.

Thus in Africa, as in US and Europe, researchers have not found that the virus spread among people living together, except for sexual partners and transmission between mothers and children. If mosquitoes, bedbugs, lice or other insects living in a crowded African house could spread the virus, we could have expected to find more infected people in the households of AIDS patients.

Another reason why transmission by insects is unlikely is the tiny amount of blood on an insect’s mouth parts, together with the small quantity of the HIV that seems to be present in the blood of infected persons. Also, HIV circulates in the blood at lower levels than malaria and other insect-borne diseases.

The mosquito does not take enough units of HIV from the infected person to initiate an infection. Even if it’s possible for the mosquito to inject HIV into the uninfected person, the person would have been bitten by 10 million mosquitoes who had been previously been feeding on an HIV positive host in order to receive one unit of HIV. Why mosquitoes cannot transmit HIV.

Also, mosquitoes’ mouth parts do not operate like a hypodermic needle. The tube which injects the host with saliva is separate from the canal which the mosquito uses to suck blood from the same host. Therefore blood only flows into the mosquito and only saliva is injected; blood is not flushed out of the same canal.

Finally, Insect-borne diseases like Encephalitis and malaria are spread because they multiply within the mosquito, these diseases then move into the insect’s salivary glands and are injected into the host with the saliva. If a mosquito feeds on an HIV-positive person, the virus cannot survive and replicate within the mosquito’s gut as HIV requires specialist cells found only in humans in order to multiply.

All these evidences lead to conclude that the virus is transmitted everywhere in the world in the same basic ways (sex, blood, mother-to-child), and never through mosquito bites.

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