Toby Murcott of BBC science: HIV's secrets are being revealed

Tuesday has been declared World Aids Awareness Day.

This year, attention is being drawn to the fact that 7,000 young people become infected with HIV - the virus that causes Aids - every day.

The majority are aged between 15 and 24.

Ninety-five per cent of people living with HIV and Aids are in the developing world, where it typically infects young healthy adults - effectively targeting the people whose energy and wages communities depend on for survival.

South Africa, one of the countries worst affected, has announced a multi-million dollar campaign to alert its population, as concern grows over the social and economic impact of the disease.

In Sub-Saharan Africa 2 million people will have died of Aids this year - four times the total for the rest of the world.

Macho attitudes blamed

According to a leading development body, macho attitudes are helping to spread Aids around the world,

Health education classes can help slow the spread of Aids

The Panos Institute says machismo among men is leading to unsafe sex which is putting women at particular risk of infection.

In many countries, women are considered less important than men, which makes it difficult for them to negotiate safe sex, according to the agency.

The financial dependence of women, their lower educational standards and their fear of appearing too sexually aware also made them more vulnerable.

Panos' report, Aids and men: Old problem, new angle, attempts to make men take more responsibility for safer sex and a more mature attitude to drugs.

The report calculates that between 300-400 million men around the world - some one in three - lead sexual lives that put them or their partners at risk of HIV infection.

Four out of five injecting drug users were also men, said the report.

Women more at risk

Martin Foreman, director of Panos' Aids programme, said: "Eighty per cent of drug injectors are men, and men have more sexual partners than women.

"Yet while men are driving the Aids epidemic, the overall impact is that worldwide, women are contracting HIV at a faster rate."

A man with HIV has on average a one in 500 chance of passing the virus to a woman in a single act of unprotected vaginal sex.

However, the chances of a woman transmitting the virus to a man are one in 1,000.