Viral load. How much of a virus there is in the body of an infected person. We often use the term for an HIV infection. A high viral load means a lot of the virus is present; a low viral load means there’s a lot less of it in the body. For HIV, with a low viral load, the virus is less likely to pass on to someone else’s body. Successful HIV treatment lowers the viral load, and it can become undetectable: it’s so low that it doesn’t show up when you test for the viral load. When someone’s HIV viral load is undetectable, the virus is no longer contagious in that person, as long as they stay on treatment and their viral load stays that low. In that situation, someone else cannot become infected with HIV from contact with that person and their body fluids.