HIV (Human Immunodeficiency Virus) is an incurable virus, which can cause a life-threatening condition called AIDS (Acquired Immune Deficiency Syndrome).

A person who has been infected with HIV is said to be HIV-positive

There are two main types of HIV: HIV-1 and HIV-2. The most aggressive form of the virus is HIV-1.

If untreated, HIV can cause so much damage that the infected person's immune system no longer works properly. When this happens, the person is said to have developed AIDS.

Although HIV reproduces very rapidly, it is referred to as a 'slow virus'. This is because it takes a long time - many years, in most cases - before it causes so much damage that a person gets ill.

HIV differs from other viruses in that it specializes in attacking the very immune cells - white blood cells known as Helper T cells, or CD4 cells - that are designed to rid the body of infections.

By infecting and ultimately destroying Helper T cells, HIV seizes control of the body's immune system. Infected cells no longer behave as they should and instead of helping to fight the disease, they actually spread it.

There is no cure for HIV, so although drugs can help to keep the virus under control, they cannot completely get rid of the infection.