Men who have sex with men are now nearly 20 times more likely to be infected with HIV than the general population, yet they often receive as little as 1 per cent of global funding.

"The story is one of abject failure on the part of the institutions that have been charged with leading the response to HIV/AIDS at local, national and international levels," said the chief executive of the American Foundation for AIDS Research, Kevin Frost.

"Men who have sex with men continue to have little or no access to HIV services of any kind and as a result are plagued by high rates of infection."

Further data on the growing gay epidemic is due to be presented today at the XVII International AIDS Conference in Mexico City.

Until recently, HIV was seen as a threat to everyone. Now experts, including the head of the World Health Organisation's HIV/AIDS programs, Kevin de Cock, acknowledge that outside sub-Saharan Africa, where infections are largely driven by heterosexual transmission, HIV is mostly confined to male-to-male transmission, injecting drug users and sex workers and their clients.

Yet governments have focused on generalised epidemics, while ignoring the groups most at risk.

"These epidemics are happening in countries where men who have sex with men are hidden, highly stigmatised populations … It is not just family and community stigma, it is also legal stigma," said the director of the Johns Hopkins University centre for public health and human rights, Chris Beyrer.

"More than 80 countries still have laws criminalising these behaviours … At least nine still have the death penalty for same-sex behaviour."

Thailand's epidemic is one of the most worrying, he warned. HIV prevalence in Thailand among men under 22 years of age who have sex with men rose from 12 per cent in 2003 to 22 per cent in 2006. The rate of HIV in Thailand's general population is less than 2 per cent.

In Africa, men who have sex with men are also 10 times more likely to have HIV than the general population, Professor Beyrer said, while the epidemic in South America is now mostly among gay men.

"There is an urgent need to respond to this, yet there is endless denial out there that these epidemics exist, and as a result they are seriously underfunded," Professor Beyrer said.

These men, in desperate need of health care and prevention services such as access to condoms and safe sex information, are either excluded from health services or exclude themselves for fear of discrimination.

Wipas Wimonsate, a medical researcher from Thailand's Ministry of Public Health, said a recent study of male-to-male transmission in the Bangkok area found rates of HIV had climbed from 17.3 per cent in 2003 to 30.7 per cent in 2007.

Alarmingly, "none of the men who tested positive to HIV during the study knew they were positive", he said.

Peter Piot, the outgoing executive director of the Joint United Nations Program on AIDS, said the epidemic in male-to-male transmission in Asia "is reminiscent of what was happening in Western countries such as the US and Australia in the 1980s".

"In just about every major Asian city for which we have data, there's been a significant increase of HIV among men who have sex with men," he said.

In Beijing, a 2005 survey of men who have sex with men showed 1 per cent were living with HIV. Two years later, that figure had gone up to 6 per cent.

In Karachi, infections among male sex workers doubled to 8 per cent in the same time frame.

While more people in low- and middle-income countries were on HIV treatment than ever before, Dr Piot said the epidemic continued to outstrip the response.

"For the 1 million people newly on treatment, there were 2.7 million newly infected - that's nearly 7500 people infected with HIV every day."

David Wilson, from the World Bank's global HIV/AIDS program, said: "We need to keep focused on injecting drug users and sex workers, but we also need to increase resources to men who have sex with men.

"In most concentrated epidemics we shouldn't be spending too much money on the general population, who are at low risk.

"Globally, we have been a bit slow to realise that."

But there is at least one sign that the times may be changing. The UN General Assembly special session on AIDS held its first ever session dedicated to the topic in June.