The letters in the acronym AIDS stand for Acquired Immune Deficiency Syndrome.

This disease was first identified in 1980 and is as yet incurable. It is caused by a blood-borne virus, HIV, (Human Immunodeficiency Virus). When someone is first infected with HIV, there are usually no symptoms and tests for HIV antibodies come up negative. Some people get an acute flulike illness three to six weeks after infection. One to two months after this HIV antibodies can be detected in the blood - at this stage, the person is said to be HIV-positive. If someone is HIV positive, they may still feel fit and healthy, since the virus can remain dormant in the blood for years before developing into AIDS. At that stage of the disease the immune system has been undermined to such an extent that all kinds of infections can take hold; the person is then said to be suffering from AIDS. The symptoms include weight loss, diarrhoea and swollen glands. As the body's immune system is systematically destroyed, the sick person is more and more likely to get infections caused by viruses and bacteria.

AIDS can be transmitted by sexual contact, shared syringes among drug users, or the use of infected blood products. Most people who contract HIV do so through sexual contact. Blood, semen and other body fluids may all contain enough HIV for the disease to be transmitted. This is why many AIDS prevention campaigns concentrate on educating people about safe sex.

At present, medical research is concentrating on developing drugs which will stop new HIV particles from forming. The difficulty in achieving this is that HIV, like all infectious organisms, can mutate rapidly. The new strains are often resistant to the drugs which would normally wipe them out. If only one drug is used, it will become useless once the virus has developed resistance to it. The answer seems to be to use a combination of drugs, so that strains which are resistant to one drug will have a better chance of being knocked out by the others. By using this type of combination therapy, levels of HIV in a patient's blood could be greatly reduced. The drawback to this kind of therapy is that it is very expensive. If all AIDS sufferers in the UK were to get these drugs, the total bill would be around 40m. To date, vaccines have proved useless in the fight against AIDS, as the virus mutates too rapidly. Similarly, anti-HIV antibodies seem to be ineffective at wiping out HIV.

Currently, an estimated 21.8 million people (roughly 0.5% of the world population) are living with HIV/AIDS. New infections occur at a rate of six per minute. It is estimated that about 6 million people have died of AIDS since the disease was first identified.