MEXICO CITY – More than 25,000 people from around the world have descended on Mexico's sprawling urban capital this week to participate in the 17th International AIDS Conference, which has brought together leading researchers, activists and health and development experts.

The world conference, the first of its kind to be held in Latin America, was inaugurated yesterday afternoon and will run throughout the week, featuring presentations and speeches by participants from 188 countries.

Despite some heartening advances in treatment coverage for people living with HIV/AIDS, and a 10 percent global decrease in new infections last year, this week's conference is expected to focus on several emerging challenges that could threaten recent progress. Those challenges include a resurgence in HIV infection rates among gay men, the threat posed by a mutated and transmittable version of the HIV virus that is resistant to drug treatment, and other obstacles associated with providing universal coverage and treatment by 2010 – an internationally agreed-on goal that appears increasingly lofty.

Since first being discovered in the early 1980s, HIV has infected 58 million people, and AIDS has killed 25 million.

Craig McClure, executive director of the International AIDS Society, the group responsible for organizing the conference, says he expects the event to focus on human-rights promotion, treatment, prevention and the strengthening of health systems.

Some of the more contentious topics that will be addressed are male circumcision as a useful prevention measure, the future of a possible HIV vaccine and using antiretroviral drug treatment to prevent the virus' transmission.

One of the most controversial issues is expected to be the claim made earlier this year by the Swiss AIDS Commission that people with HIV who are being treated with antiretrovirals, to the point that they now have an undetectable viral load, are no longer able to transmit the virus to others. The claim has caused great concern and criticism in the international AIDS community, where many argue it is unwise and counterproductive to green-light unsafe sex practices after years of preaching protection.

An average of 6,800 people are infected every day with HIV, though drugs have proved effective in controlling the virus and preventing it from progressing to AIDS.

To date, no vaccine for the virus has been found.