Medical professionals have identified several ways in which people can be infected with the Human Immuno-deficiency Virus (HIV): Through sexual contact with an infected partner and multiple sex partners -- the virus can enter the body through the lining of the vagina, vulva, penis or rectum during sex. But the risk level of oral sex is yet to be determined. Any genital infection, in either partner, greatly increases the risk of infection. Oral/genital contact can theoretically transmit HIV if lesions are present in the mouth or on the genital organ.

By sharing needles or syringes with someone who has been contaminated also spreads the virus. Needle sharing has been blamed for much of the spread of HIV. This applies to drug addicts who "shoot up" in groups with the same needle and the same syringe. In majority of the cases babies born to infected mothers too are afflicted. Further research is on to find out preventive methods to control this kind of transmission. Mother-to-baby transmission can occur during pregnancy through the placenta or during childbirth. It can also occur through breastfeeding. Blood transfusion is another major way the virus spreads. In 1986, tests were developed to identify HIV in blood products and to treat them to destroy the virus. Today, blood is screened and treated before transfusion, decreasing the risk greatly.

In order to be infectious, the virus has to enter the body and get in contact with the blood of the exposed person. Transmission of the virus, probably, requires a minimal amount of virus or a "threshold" to induce infection. Below this level, the body can get rid of the virus and prevent its installation.

The AIDS virus has been principally detected in the blood, semen, and vaginal secretions of the infected subjects. These body fluids are the principal vectors of the virus. The virus has also been detected in small amounts in other body fluids like saliva, tears, sweat etc.

No studies have indicated that the virus can spread through kissing. At this time, however, it is not known what the risk of infection is from "deep" kissing, which can involve the exchange of large amounts of saliva, or from oral sex. HIV does not spread through sweat, tears, urine or feces.