Aids was first identified in the early 1980s, but the first case of the disease may have occurred much earlier - in Africa in the late 1950s. Drug treatments and public education have curbed its spread in some parts of the world. In Africa, most people infected with HIV are unaware of the fact.
What is Aids?
Aids (acquired immune deficiency syndrome) is a weakening of the immune system by the human immunodeficiency virus, HIV. The sufferer loses the ability to fight infection, and may fall victim to illnesses such as pneumonia, diarrhoea, and tumours.
Where does Aids come from?
Most researchers believe humans acquired Aids from chimpanzees - which sometimes carry a similar virus - by eating them or being bitten by them. A minority view holds that it was spread by a vaccine made from infected chimpanzee tissue.
Is there a cure?
There is no cure for Aids, and no vaccine to prevent infection with HIV, but there are drugs that can slow down the spread of the virus and the rate at which it weakens the immune system. In some patients the virus has been reduced to undetectable levels.
How is Aids spread?
The HIV virus is transmitted in body fluids including blood, semen, vaginal fluid and breast milk. It is most commonly passed on during sexual intercourse, shared use of hypodermic needles, or from mother to child. It can also be transmitted by blood infusion, but not by ordinary social contact.
How big is the problem?
According to the UN, Aids is now the number one overall cause of death in Africa and is in fourth place among all causes of death worldwide. It's estimated that 2.8 million people died of Aids in 1999.
Is the crisis deepening?
Deaths from Aids have been falling in the richest countries thanks to effective drugs, but in many others the epidemic continues. The UN estimates that Aids will kill more than one third of young adults in some parts of Africa.
Why is Africa so badly hit?
The Aids epidemic began in Africa, but in many cases governments were slow to respond. The problem has been exacerbated by poverty, illiteracy, weak educational and public health systems and the low social status of women.
What can be done?
Better testing for HIV is a priority in many countries, to help carriers of HIV become aware of the fact. The UN says poor countries can achieve a lot by improving education and access to condoms, even if they cannot afford expensive drugs.
What are the symptoms of HIV infection?
Only a blood test can prove HIV infection. Many infected people have no symptoms for many years, but early signs may include weight loss, a dry cough, recurring fever, tiredness, swollen glands and diarrhoea.