If sharing a syringe can transmit the AIDS virus, then why not a mosquito bite?

 Why do mosquitoes not suck virus like AIDS when they suck blood from humans having AIDS-like disease?

Mosquitoes suck whole blood together with all its contained viruses, bacteria and other pathogens, including HIV. Luckily for humans, the HIV virus cannot be spread by mosquitoes.

This is because of several reasons accounting for the inability of mosquitoes to transmit HIV.

First of all, the feeding mechanism of mosquitoes does not promote transmission, it is not like a hypodermic needle injecting blood .

The sucking "snout" of a mosquito has six mouthparts. Four of these are used for piercing the skin that the mosquito is biting. The other two mouth parts consist of two tubes. One tube sends saliva into the host and the other sends blood up into the mosquito.

This two tube system does not allow for mixing. It is one major reason why mosquitoes are unable to transmit HIV. Only saliva is injected into humans when a mosquito bites and thus HIV positive blood that a mosquito may have previously ingested is never transmitted to other humans.

In addition, unlike with mosquito borne diseases, HIV is unable to replicate within the mosquito's gut. This is because the receptors that HIV requires to replicate are not present in mosquitoes. In humans, HIV must bind to CD4 T cells and the CCR5 or the CXCR4 co-receptors to begin replicating. No such cells and co-receptors exist inside the mosquito's gut. Thus, the virus has no way of replicating or migrating to the mosquito's salivary glands. Instead, HIV particles are digested by the mosquito alongside its blood meal. During this digestion process, HIV particles are completely destroyed.

Finally, mosquitoes suck only 0.0005 ml of blood per meal. There is very little virus in that volume. Coupled with the unique feeding mechanism of mosquitoes described above, it would take about ten million mosquito bites to transmit one unit of HIV.

Accidentally swallowing a mosquito or squashing one cannot lead to HIV infection either. In these situations the mosquito once again carries an insufficient amount of HIV positive blood to cause a new infection.