What are HIV and AIDS?

What are HIV and AIDS?

HIV is a virus which attacks the human immune system, the body's defence against disease. A person with HIV may feel completely well and have no symptoms.

In time, a person with HIV may develop particular rare illnesses or cancers because their immune system is weakened. When this happens, the person is said to have AIDS.

How does HIV cause AIDS?

HIV affects various parts of the body's immune system. The most important damage it causes is to certain white blood cells known as CD4 cells or T-helper cells. These cells are found in the lymph nodes as well as circulating round the body.

CD4 cells set other parts of the immune system in motion when organisms which cause disease are present in the body. These organisms include viruses, bacteria, protozoa and fungi. They can cause disease if not controlled by the immune system.

The CD4 cells of an HIV-infected person mount a defence against the invading HIV, and it may be held at bay for many years. But the virus is not completely destroyed, and it continues to attack the CD4 cells. Eventually the number of CD4 cells declines and the virus numbers rise.