AIDS (acquired immunodeficiency syndrome) is a disease in which the body's immune system breaks down and is unable to fight off certain infections, known as "opportunistic infections," and other illnesses that take advantage of a weakened immune system.

When a person is infected with HIV, the virus enters the body and lives and multiplies primarily in the white blood cells. These are the immune cells that normally protect us from disease. The hallmark of HIV infection is the progressive loss of a specific type of immune cell called T-helper or CD4 cells.

As the virus grows, it damages or kills these and other cells, weakening the immune system and leaving the individual vulnerable to various opportunistic infections and other illnesses, ranging from pneumonia to cancer. The U.S. Centers for Disease Control and Prevention (CDC) defines someone as having a clinical diagnosis of AIDS if they have tested positive for HIV and meet one or both of these conditions:

• They have experienced one or more AIDS-related infections or illnesses.
• The number of CD4 cells has reached or fallen below 200 per cubic millimeter of blood (a measurement known as T-cell count).

In healthy individuals, the CD4 count normally ranges from 450 to 1200.

How does AIDS develop?

HIV slowly attacks and destroys certain white blood cells in the body ( CD4+ T cell) . In normal conditions, these cells help the body to fight infections and diseases caused by viruses and bacteria. When HIV has invaded a person, these cells no longer work properly because HIV slowly destroys them. This means that HIV will also destroy the body's ability to fight diseases.

Cells with CD4 receptors at the site of HIV entry become infected and viral replication begins with them. After initial entry of HIV and establishment of infection, HIV virus may enter the systemic circulation and be carried to sites widespread within the body, where more CD4 cells are destroyed, leading to opportunistic infections related to AIDS.

AIDS is the advanced stage of HIV infection. The development of this disease undergoes certain phases:-

• Phase 1 - Begins when HIV infects an individual.

• Phase 2 - Continues with a phase where the virus develops but the patient exhibits no signs or symptoms.

• Phase 3 - Progresses to signs and symptoms that worsen the body's defence mechanism.

• Phase 4 - Patients will develop rare diseases called opportunistic infections' such as Pneumocystis carinii Pneumonia and cancers including Kaposi's Sarcoma.

• Phase 5 - The person is confirmed as an AIDS patient. In this phase the defence mechanism is badly damaged and they can no longer fight off bacteria, viruses and other germs.

What are the symptoms of AIDS?

An HIV patient may have the following symptoms:

• Unexplained weight loss of more than 10%.

• Chronic (persistent) diarrhoea and cough.

• Prolonged fever. The fever can either be periodic or persistent.

• Enlarged lymph nodes especially in the neck, armpits or groin.

• Recurrent herpes zoster infection. Herpes zoster is a viral infection of the nerves and appears as blisters on the skin.

• Candidiasis of the mouth and throat is a disease caused by a fungus.

• Recurrent herpes simplex infection. (Herpes simplex is a viral infection of the skin and is often seen as blisters around the mouth or genitals.)

What are the complications of AIDS

Complications depends on the stage of HIV infection. Some of the complications include:

• Pneumocystis carinii pneumonia, which can be life threatening. This disease damages the AIDS patient's lungs.

• Cytomegalovirus retinitis is a potentially severe AIDS-related eye infection that can lead to blindness.

• Kaposi's sarcoma is a type of AIDS-related cancer that causes characteristic purple or pink skin tumours that are flat or slightly raised.

• AIDS wasting syndrome which involves major weight loss, chronic diarrhoea or weakness, and constant or intermittent fever for at least 30 days.