People are forgetting to practise safe sex because they no longer fear dying from HIV/AIDS, says the doctor who won the Nobel prize for helping to discover the virus.
Treatment advances mean "some people in my country, France, and other Western countries have become complacent -- they see HIV/AIDS as a chronic disease -- not as one that can kill," virologist Francoise Barre-Sinoussi said.
The doctor shared the Nobel Prize last year with fellow French virologist Dr Luc Montagnier for their discovery in 1981 of the human immunodeficiency virus (HIV) that causes AIDS.
Barre-Sinoussi noted there has been a huge leap forward in treatments for HIV/AIDS with a cocktail of drugs that reduces the level of virus in the body and likewise lowers the risk of passing on the pathogen to others.
But she told AFP she worried that people's confidence in retroviral drugs had created a false sense of security, leading to an increase in unprotected sex.
Speaking on the sidelines of a medical conference last week organised by French charity Fondation Merieux in New Delhi, she noted a "frightening" rate of new male-to-male infection in some Western countries such as France.
"We should tell the truth about HIV/AIDS -- that new treatments can be very effective, helping them live years longer," said Barre-Sinoussi.
But she added that HIV/AIDS patients are prone to other illnesses, especially cancers. They can also be resistant to the life-saving drugs, creating "major complications."
Between 2001 and 2006, male-to-male sex was the largest HIV transmission category in the United States and the only one associated with an increasing number of HIV/AIDS diagnoses, according to the US Centers for Disease Control and Prevention.
About 56,300 people were infected with HIV in the United States in 2006, according to the organisation, with gay and bisexual men accounting for about half of all new infections.
In the United States and all around the world, fears of being stigmatised discourage people from being tested, non-governmental bodies say.
In the 1980s in the West gay leaders, dismayed by the deaths of so many from the virus, mounted an aggressive grassroots movement that triggered government action and prevention campaigns among the homosexual community.
HIV infections among gay and bisexual men fell dramatically for a decade but rates have been rising again since the mid-1990s.
The virus is also having a disproportionate effect on men who have sex with men in nations where the epidemic is just getting a foothold.
Professor Mark Wainberg, head of Montreal's McGill University AIDS Centre, echoed Barre-Sinoussi's concerns.
With the advances in treatment "the voices that spoke for safe sex are often silent," he told AFP at the same New Delhi conference.
"People are saying 'look how well the drugs work -- they work for a long time.'"
The public needs to understand the drugs themselves can be toxic and statistics are showing alarming rates of cancer in HIV-affected people, he added.
"The data from our studies indicate the average age of people getting HIV/AIDS is 35 -- these are mature individuals, not kids," he said.
"Some people are throwing caution to the wind."
Around the world, about 33 million people are living with HIV/AIDS and two million die each year. It has killed at least 25 million.
At the same time, Barre-Sinoussi said she was optimistic researchers would find an AIDS vaccine despite many major research setbacks.
"We really have to go back to very basic science and think differently... think out of the box," she said.