It produces lethal vibrations in the protein coat of micro-organisms, thereby destroying them. The effect of the vibrations is similar to that of high-pitched noise shattering glass.

However, the line of attack can be perfected so that the proteins which coat human cells remain unaffected.

So far experiments have been done on E. coli bacterial cells, Tobacco Mosaic Virus cells, as well as human and hamster cells.

After several attempts, the researchers found a level which "inactivates both viruses and bacteria while leaving sensitive materials such as mammalian cells unharmed".

Lead researcher Professor Kong-Thon Tsen, of Arizona State University, said: "The research so far suggests that ISRS will be ready for use in disinfection and could provide treatments against some of the worst, often drug-resistant, bacterial and viral pathogens."

Merck & Co. said Friday that it is ending enrollment and vaccination of volunteers in the study, which was partly funded by the National Institutes of Health.

It was a high-profile failure in the daunting quest to develop a vaccine to prevent AIDS. Merck's vaccine was the farthest along, considered the most promising and was closely watched by experts in the field.

Officials at the company, based in Whitehouse Station, N.J., said 24 of 741 volunteers who got the vaccine in one segment of the experiment later became infected with HIV, the virus that causes AIDS. In a comparison group of volunteers who got dummy shots, 21 of 762 participants also became infected.

"It's very disappointing news," said Keith Gottesdiener, head of Merck's clinical infectious disease and vaccine research group. "A major effort to develop a vaccine for HIV really did not deliver on the promise."

Scientists have long known that HIV can go dormant, only to emerge again later and run rampant through the body.

"We know the virus can hide out," Weinberger said. "How does it hibernate? We wanted to look at the basic components of the virus."

In the laboratory, the two created a "gutted" HIV virus, or one with molecular components removed. The scientists then looked at the components necessary for the virus to replicate.

Scientists already know that a protein called Tat is connected to HIV's ability to go dormant. After a year of work, the Princeton team identified enzymes that act on the protein. These enzymes modify, or "decorate," the protein. Together, the Tat protein and the enzymes create the cascade of chemical reactions that push HIV in and out of latency.

So far, the scientists have pin-pointed the target, but have no way, at present, to affect it.

"How challenging this is going to be depends on where (what state) the doctor practices," said Dr. Nancy Nielsen, a Buffalo, N.Y.-based physician who sits on the governing board of the American Medical Association.

And then there's the daunting issue of dealing with a patient who has HIV, which some pediatricians and family doctors have rarely faced.

Many primary care doctors customarily refer a patient with HIV to a specialist better equipped to treat the virus and put the patient in touch with support services. That's expected to continue.

But the primary doctor will be expected to break the initial news of the diagnosis to the patient - a task requiring skills some physicians don't always demonstrate, said Dr. Kimberly Manning, an internist at Atlanta's large public hospital, Grady Memorial.

"It's not like someone's cholesterol being high," she said. With HIV, a physician must be prepared to empathize, educate and guide patients into such steps as notifying intimate contacts, she added.

And there is the issue of cost. A routine blood test for HIV can cost between $3 and $5, some health experts say. New rapid tests, done through finger pricks or oral swabs, cost $15 or more.

Despite infection rates that are ravaging Africa and other parts of the developing world, Bill Clinton and Bill Gates insisted Monday a "happy ending" is in the offing and AIDS will be vanquished.

The former U.S. president and the Microsoft chairman conceded at the International AIDS Conference Monday the turning point in the pandemic has not yet been reached and may not come until scientists develop a vaccine or some other form of preventive tool. Clinton, whose charitable foundation is largely focused on the HIV/AIDS cause, said visiting endemic regions gives him optimism for a AIDS-free future.

On a recent trip to Liberia, a country nearly destroyed by civil war, the college students he met were as bright and ambitious as any he has encountered.

"The source of optimism is the human material," he said. "There is no shortage of intelligence, effort, dreams and drive anywhere in the world."

The radical change to HIV testing guidelines will be released in June or July, says Kevin Fenton, MD, PhD, the new director of the CDC's National Center for HIV, STD, and TB Prevention. Routine HIV tests in doctors’ offices and clinics will no longer require the pretest counseling now a part of all HIV testing.

Fenton, joined by former CDC AIDS chief James Curran, MD, MPH, now dean of Emory University’s Rollins School of Public Health, spoke today at a news conference marking the 25th anniversary of the AIDS pandemic.

"Most HIV is transmitted by the 25% of infected people who do not even realize they are infected," Fenton said. "We need to dramatically expand access to HIV testing by making it a routine aspect of clinical care."

Five hundred thousand Americans are among the 25 million dead from AIDS. A million more Americans now carry the virus -- and nearly 16,000 died in 2004. If you think it's easy to live with the AIDS virus, if you think AIDS drugs are a cure, think again.

"Living with HIV is not easy," Fenton said. "The drugs can cause serious side effects and sometimes don't work for the long term. We need to reduce the number of people who become infected in the first place. Twenty-five years into the epidemic, prevention is the only cure we have."

Overall, the report says more than 3m people died of Aids-related illnesses in 2005. Of these, more than 500,000 were children.

The report says Sub-Saharan Africa is still hardest hit by HIV/Aids.

Two thirds of the people living with HIV - 25.8m - are in this area.

In 2005, 2.4m people in Sub-Saharan Africa died of an HIV-related illness, and a further 3.2m were infected with the virus.

Andrew Stimpson, 25, was diagnosed HIV-positive in 2002 but was found to be negative in October 2003 by Chelsea and Westminster Healthcare NHS Trust.

Mr Stimpson, from London, said he was "one of the luckiest people alive".

The trust said the tests were accurate but had been unable to confirm Scotsman Mr Stimpson's cure because he had declined to undergo further tests.

A statement from the trust said: "This is a rare and complex case. When we became aware of Mr Stimpson's HIV negative test results we offered him further tests to help us investigate and find an explanation for the different results.

The body has many defence mechanisms against viruses. However, in the case of HIV, it has not yet been proven that the body can clear itself completely of the virus.

In some patients, HIV never turns into full-blown Aids, which scientists hope will give them clues to how to beat the virus.

There have been a number of anecdotal reports of people who appear to be immune to or have shaken off HIV. But the science is sketchy.

Deborah Jack, chief executive of the National Aids Trust, said: "The virus is extremely complex and there are many unknowns about how it operates and how people's bodies react to it."

An individual would be able to tell within 20 minutes whether they had the infection or not, in the privacy of their own home.

Many have expressed fears that people who find out in this way may kill themselves and hence testing should be supervised and counselled face to face.

Home HIV testing kits are banned in the UK for such reasons. However, some buy unapproved kits over the internet.