Does rectal fluid contain HIV?
In an HIV-positive person, the mucous membranes throughout the body can contain a lot of HIV. This is because these membranes are rich in immune cells, which are the cells that HIV likes to infect and replicate within. Since so much HIV replication can occur at the mucous membranes, the virus is able to enter the mucus that the membranes produce.
The mucous membranes of the rectum, and the mucus they produce (rectal fluid), are no exception. Several studies show that HIV can be found in the rectal fluid of a person living with HIV. In fact, one study of 64 HIV-positive men (of which about half were on antiretroviral therapy) found that, overall, the average amount of virus in their rectal fluid was higher than in their semen and blood.
Why might rectal fluid contain more HIV than other bodily fluids? It turns out that the majority of the immune cells in the body including the cells that are a major target for HIV are located in the mucous membranes of the gastrointestinal tract, which includes the rectum. There are a lot of immune cells in the gastrointestinal tract because it has a very large surface area. Also, a large number of immune cells are needed to help to protect the gut from the “foreign” germs in our food and to control the growth of the “friendly” germs living in our gut. The high concentration of immune cells means that the majority of HIV replication in someone with HIV may be happening in the gastrointestinal tract, including the rectum. This may explain why so much HIV can be found in the rectal fluid. Rectal fluid has implications for HIV transmission through anal sex when the HIV-negative person is the insertive partner (that is, inserts their penis into a partner’s anus). Research show that this type of anal sex can carry a significant risk of HIV transmission. Rectal fluid undoubtedly contributes to the risk of HIV transmission through anal sex where the insertive partner is HIV negative.