The virus was “perilously close to a tipping point” where it would explode across the population and spread “like wildfire”. The result would be “tens of millions of infections,” said Peter Piot, executive director of the United Nations agency UNAIDS.

Speaking in Washington on the eve of World Aids Day, Mr Piot said that “no country on Earth will escape the impact” of the economic cost if the virus marched on at its current rate. By 2010, it would reach £8.8 billion a year.

High-risk groups still dominate the Aids problem in Russia and China. But allowing the virus to leapfrog into the wider population as it has elsewhere could swallow up resources for African countries. HIV infections in Africa remain far higher than those in the Asia-Pacific nations. In China, 0.1 percent of people aged 15 to 49 are infected, compared with 7.5 per cent in sub-Saharan Africa.

But that picture could change quickly. Mr Piot recalled that in South Africa the population affected doubled to 1 per cent in five years and then rocketed to 20 per cent in just seven years. India’s infection rate is also relatively low but the number of people infected, at 5.1 million, is second only to South Africa.

The experts also criticised the focus on sexual abstinence in President Bush’s £7.7 billion Aids relief plan known as “ABC” — Abstinence, Being faithful and using Condoms.

“Millions of women became infected while monogamous and faithful, so focusing solely on personal behaviour and risk absolutely does not go far enough,” said Geeta Rao Gupta, head of the International Centre for Research on Women. Mr Piot added: “Abstinence isn’t an option for women who are violated or abused. Our prevention strategies have to fit the realities of women’s lives. Marriage was not made for sexual abstinence.

” With the emphasis on prevention, the experts urged US policymakers to devote resources to strategies that would help women to protect themselves.

These include microbicides to kill the virus, which women can use without their partner knowing, tougher punishments for rape and renewed efforts to reduce the incidence of child marriage.

The number of women affected by HIV/Aids has increased steadily since 2002. Women now account for nearly half the estimated 37.2 million HIV-positive adults in the world.

Even in America, Aids is the leading cause of death among African-American women between the ages of 25 and 34.

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