WASHINGTON — The world's largest AIDS conference returned to the U.S. on Sunday with a plea against complacency at a time when the epidemic is at a critical turning point. "We can start to end AIDS," one expert said.

There is no cure or vaccine yet, but scientists say they have the tools to finally stem the spread of this intractable virus – largely by using treatment not just to save patients but to make them less infectious, too.

"Future generations are counting on our courage to think big, be bold and seize the opportunity before us," said Dr. Diane Havlir of the University of California, San Francisco, a co-chair of the International AIDS Conference.

The Obama administration calls the goal an AIDS-free generation, and Health and Human Services Secretary Kathleen Sebelius said what was "once a far-off dream, now is in sight."

But the challenge that more than 20,000 scientists, doctors, people living with HIV and policy-makers will grapple with this week is how to make this promising science a practical reality. What combinations of protections work best in different regions, from AIDS-ravaged poor countries to hot spots in developed countries like the U.S.? With HIV increasingly an epidemic of the poor and the marginalized, will countries find the will to invest in the most vulnerable?

And where's the money? The world spent $16.8 billion fighting AIDS in poor countries last year, but that's still $7 billion a year shy of the amount needed to get the 15 million people most in need of treatment on drugs by 2015, the United Nations says. Eight million take them today.

Experts told the conference Sunday that a global recession and fatigue in the AIDS fight threaten those dollars.

"We must resolve together never to go backwards," said Dr. Elly Katabira, president of the International AIDS Society.

Added Havlir, "It would be an extraordinary failure of global will and conscience if financial constraints truncated our ability to end AIDS just when the science has shown us that this goal is achievable."

One key step in stemming HIV's spread is to treat more infected pregnant women so they don't spread the virus to their babies. Some 300,000 children were infected last year, but that number is steadiliy dropping.

UNAIDS chief Michel Sidibe put a face to that investment Sunday, introducing a mother from Nigeria who received U.S.-funded treatment that meant her daughter, now 13, was born without HIV.

"I do not want to be the lucky exception," Florence Uche Ignatius told the crowd.

Added her daughter, Ebube Francis Taylor, "I want all children to be born just like me, free of HIV."

But the hurdles are huge. Some 34.2 million now are living with HIV around the world. The epidemic is worst in developing countries, especially in Africa. Progress has stalled even in the U.S., which has seen about 50,000 new infections every year for a decade. Here, nearly 1.2 million people live with HIV, and one in five doesn't know it. African-Americans are particularly hard-hit, accounting for about half of infections.

Getting medication is a problem for the poor here, too. Sebelius said the Obama administration had released nearly $80 million in grants this week to increase access to treatment, and is trying novel partnerships with community groups to help people stick with the medication daily for life. First up is a pilot program with the MAC AIDS Fund that will send text-message reminders about medication to young people living in the South.

The AIDS conference – remarkable for giving a forum not just to leading scientists but to people who live with HIV – hasn't returned to the U.S. since 1990, in protest of the longtime ban on people with the virus entering the country. The Obama administration lifted the travel ban in 2010, finishing a process begun under the Bush administration. Not lifted was a ban on sex workers and injecting drug users, and protesters briefly interrupted the opening news conference to decry their absence from the meeting.

People living with HIV marched through downtown Washington Sunday to urge the public and policy-makers to pay attention to a disease that, in this country, doesn't get much publicity anymore.

"We're everyday people. Anybody and everybody can catch this," said Ann Dixon, who traveled from North Little Rock, Ark., to attend the march. She learned she had HIV in 1997.

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  • 2012 International AIDS Conference

    People walk toward the U.S. Capitol as part of the AIDS March in Washington, on Sunday, July 22, 2012.

  • 2012 International AIDS Conference

    Activists gathered on the National Mall on Sunday as the 2012 International AIDS Conference started in Washington.

  • 2012 International AIDS Conference

    Activists gather on the National Mall on Sunday as the 2012 International AIDS Conference started in Washington.

  • 2012 International AIDS Conference

    People gather for a march on the Capitol on Sunday as the 2012 International AIDS Conference gets started in Washington.

  • 2012 International AIDS Conference

    People walk toward the U.S. Capitol as part of the AIDS March in Washington, on Sunday, July 22, 2012.

  • 2012 International AIDS Conference

    In this photograph taken by AP Images for Aids Healthcare Foundation, marchers parade towards the Capital in the Keep the Promise on HIV/Aids Rally March on Washington, Sunday, July 22, 2012, in Washington. (Steve Ruark/AP Images for Aids Healthcare Foundation)

  • 2012 International AIDS Conference

    In this photograph taken by AP Images for Aids Healthcare Foundation, people walk around AIDS quilts placed in front of the Washington Monument on The Mall before the Keep the Promise on HIV/Aids Rally March on Washington, Sunday, July 22, 2012, in Washington. (Steve Ruark/AP Images for Aids Healthcare Foundation)

  • 2012 International AIDS Conference

    In this photograph taken by AP Images for AIDS Healthcare Foundation, Margaret Cho, left center, and Cornel West, right center, dance on stage during the Keep the Promise March on Washington and rally, Sunday, July 22, 2012, in Washington. (Larry French/AP Images for AIDS Healthcare Foundation)

  • 2012 International AIDS Conference

    In this photograph taken by AP Images for AIDS Healthcare Foundation, marchers begin the Keep the Promise March on Washington and rally, Sunday, July 22, 2012, in Washington. (Larry French/AP Images for AIDS Healthcare Foundation)

  • AIDS Quilt

    People gather around a section of the AIDS Memorial Quilt, on the National Mall in Washington, Saturday, July 21, 2012. The full quilt's display on the Mall was delayed due to rain.

  • AIDS Quilt

    Deb Bergmann, left, Dave Prochnow, Mary Prochnow, and an emotional Tim Wallin, of Alexandria, Va., are helped by volunteer Anne Balsamo, right, of Los Angeles, to find the panel honoring Wallin's partner, Gregg Berg, who died of AIDS in 1993, at the "Quilt Touch Table," an interactive browser of the AIDS Memorial Quilt, on the National Mall in Washington, Saturday, July 21, 2012.

  • AIDS Quilt

    Cole Stone-Freisina, 16, left, of Atlanta, and Stephanie Laster, right, with the NAMES Project, works on a new panel to add to the AIDS Memorial Quilt, on the National Mall in Washington, on Saturday, July 21, 2012.

  • AIDS Quilt

    People visit the AIDS Memorial Quilt on display as part of the Smithsonian Folklife Festival on the National Mall in Washington, on Thursday, July 5, 2012. An AIDS-free generation: It seems an audacious goal, considering how the HIV epidemic still is raging around the world. Yet more than 20,000 international HIV researchers and activists will gather in the nation's capital later this month with a sense of optimism not seen in many years _ hope that it finally may be possible to stem the spread of the AIDS virus.

  • AIDS Quilt

    People visit the AIDS Memorial Quilt on display as part of the Smithsonian Folklife Festival on the National Mall in Washington, Thursday, July 5, 2012. An AIDS-free generation: It seems an audacious goal, considering how the HIV epidemic still is raging around the world. Yet more than 20,000 international HIV researchers and activists will gather in the nation's capital later this month with a sense of optimism not seen in many years _ hope that it finally may be possible to stem the spread of the AIDS virus.

  • AIDS Quilt

    A man works on a quilt in memory of an AIDS victim on the National Mall in Washington on July 22, 2012.

  • AIDS Quilt

    Two women work on quilts in memory of AIDS victims on the National Mall in Washington on July 22, 2012.

  • AIDS Quilt

    A woman works on a quilt in memory of an AIDS victim on the National Mall in Washington on July 22, 2012.