Which bodily fluid is known to transmit HIV?

The transmission of HIV is primarily associated with specific bodily fluids that contain a higher concentration of the virus, making them key in transmitting HIV from one individual to another. Blood is the most significant of these fluids. It can carry the virus in a way that can lead to infection when it comes into contact with a mucous membrane or open wound of an uninfected person.

While other fluids like semen also contain the virus and can lead to transmission during sexual activities, blood is often highlighted in discussions about transmission risk due to its potency and the various transmission routes, including sharing needles, blood transfusions, and from mother to child during childbirth. On the other hand, fluids like saliva or urine have not been shown to transmit HIV effectively due to very low virus concentrations, which significantly reduces the risk of infection through those means.