HIV is a virus that infects white blood cells, primarily those called CD4 cells (also called T4 cells or T-helper cells).
CD4 cells are found in several body fluids, but mainly in blood and in genital secretions. HIV is passed, or transmitted, when the CD4 cells from one person’s blood or genital secretions get inside the body of another person.
Most of the viruses are inside cells, but some may be free in the body fluids as well. Body fluids contain many more cells infected with HIV than they do free HIV. These body fluids are the vehicles for transmission of HIV.The scientific evidence to support this method of transmission is compelling. What is known about the risk of transmitting HIV has come from two types of scientific studies: partly from studies of the virus, called virology; and principally from studies of the people who are infected with the virus, called epidemiology. The epidemiological studies came first in time. In 1981, epidemiologists began tracking cases of pneumocystis pneumonia in gay men; by 1983, when HIV was finally discovered, epidemiologists knew most of what was necessary to know about the spread of the disease. They knew that the disease, whatever its cause, was transmitted by sexual intercourse and by blood and by passage from an infected mother to her unborn child. They knew that this sort of transmission suggested that a microbe was responsible (other microbes, including cytomegalovirus and hepatitis B virus, are transmitted in precisely the same ways). In 1983, a French researcher, Luc Montagnier, reported the virology studies that described the virus that came to be called HIV.
But regardless of how compelling the scientific evidence is, misunderstanding of how HIV is transmitted is widespread and causes people a lot of worry. The purpose of this chapter is to discuss, first, what is known and what is not known about the risk of transmitting HIV, and second, how to prevent transmission. In other words, it is about how to avoid giving HIV to someone else and how to avoid getting it yourself.
Most of the public’s misconception is based on the belief that HIV is transmitted the way more common viruses, like the influenza virus, are transmitted. We think it is important to emphasize that viruses like the influenza virus and HIV are enormously different, not only in the way they are transmitted, but also in the way they cause disease.