There are 3 key factors.
1. Mosquitos don’t inject blood into people when they bite, they suck blood out. They DO inject saliva, but in tiny amounts
2. HIV can’t survive in a mosquito
3. Even if they could inject blood into you, the amount they do wouldn’t contain nearly enough of the HIV virus for you to develop the disease.
https://www.nature.com/scitable/blog/viruses101/why_cant_mosquitos_transmit_hiv/
Latest Answers