key facts and figures...
The number of adults and children infected with HIV/Aids reached 40.3 million in 2005, the highest level ever.
About 3.1 million people died in 2005; 570,000 of them were children. This is almost one million more deaths than in 2003, with five million new infections in 2005.
Acquired immune deficiency syndrome, or Aids, has killed more than 25 million people since it was first recognised in 1981.
Sub-Saharan Africa has 10 per cent of the world's population, but more than 60 per cent of all people infected with HIV.
An estimated 2.4 million people died of HIV-related illnesses in 2005 in Sub-Saharan Africa, and 3.2 million became infected with HIV.
In eastern Europe and central Asia, the number of HIV infections has risen by one quarter to 1.6 million since 2003, and the number of Aids deaths almost doubled to 62,000.
In Asia, 8.3 million people had HIV in 2005, including 1.1 million newly infected, and 520,000 Aids patients died.
An estimated 3.7 million people are infected with HIV in the Americas and western and central Europe.
The Aids virus is transmitted through sex, shared needles, and from mother to child during birth and breast-feeding.
Cocktails of drugs known as highly active antiretroviral therapy, also ARVs or HAART, can keep HIV-infected patients healthy and prevent the development of Aids. About 20 such drugs are on the market, including cheap, generic copies.
Experts agree that a vaccine offers the best hope for stopping Aids. Currently, more than 30 potential Aids vaccines are being tested in people in 19 countries but none has shown any special promise.
Condoms can help prevent the spread of Aids and activists are clamouring for the development of a gel or cream called a microbicide that could be used to prevent sexual transmission of the virus.