MINNEAPOLIS — Scientists at the University of Minnesota reported Wednesday that they found a way to block transmission of the virus that causes AIDS in animals, raising hopes of a potential breakthrough in the battle against the worldwide epidemic.

The scientists were able to prevent infection in a group of female monkeys by treating them with a gel containing a common food additive, known as glycerol monolaurate or GML, before they were exposed to the virus.

The discovery, reported Wednesday in the journal Nature, could lead to a novel and effective way to prevent sexual transmission in women, said Dr. Ashley Haase, who led the study with fellow microbiologist Patrick Schlievert.

Haase cautioned that the study was small and has only been tried in animals. But if it works this well in humans, he said, “it could contribute to saving millions of lives.”

Lorraine Teel, executive director of the Minnesota AIDS Foundation, said the research “has absolutely enormous implications.” She noted that women now account for more than half the new cases of AIDS, particularly in Africa. “If it turns out to work that way, then Wednesday should become an international holiday,” she said.

The researchers tried to strike a balance between excitement and caution as they talked about their findings.

“The results, we think, are very encouraging,” said Haase, the chairman of microbiology at the medical school.

At the same time, he said, it will require a lot more research before they know if it can stop HIV, the virus that causes AIDs in people. For years, scientists have been struggling to find new ways to curb the spread of the disease, which killed some 2 million people worldwide in 2007. An estimated 33 million people are living with HIV today, and another 2.7 million contract the disease each year..

This treatment, they say, would not help anyone already infected. The hope is that it may prevent new infections.

Schlievert noted that GML, a germkiller, has already been proven safe for human use — it’s found in ice cream and cosmetics, among other things — and costs less than a penny a dose. He decided to try it on AIDS after years of studying GML as a possible treatment for toxic shock syndrome.

In the study, the university researchers treated five rhesus monkeys with the GML gel, applied vaginally, and then exposed them to the monkey version of HIV. After two weeks, none of the five had any sign of infection; while four out of five in a comparison group quickly contracted the virus.

Five months later, however, the scientists learned that one monkey treated with GML had become infected. They’re not sure how that happened, but it’s another reason for caution, says Haase.

Experts say the study was groundbreaking in part because it tested a new theory for fighting AIDS. Haase called the approach “counter-intuitive.”

Instead of trying to fight the AIDS virus itself, they decided to try to block the natural defenses that the body uses to protect itself. That’s because, when this AIDS virus enters the body, it hijacks the immune cells and uses them to spread the infection. So in this case, they used GML to keep those immune cells at bay.

The gamble paid off. In two weeks, there was no evidence of infection in the treated animals, in spite of repeated exposure to the virus, the scientists reported. By that time, an infected monkey would have had hundreds of millions of copies of the virus in its bloodstream, they said.

The scientists can only guess why one of the monkeys developed the infection months later. Either a small amount of the virus slipped through undetected, the researchers said, or the monkey could have been exposed after the study ended.

If further studies confirm their initial results, “then this is really a fabulous new finding,” said Rowena Johnston, vice president of research for the Foundation for AIDS Research in New York. She warned that there may be scientific pitfalls ahead — some promising discoveries in the past have turned out to increase the risk of AIDS, rather than reducing it.

But, she said, “this is absolutely a great beginning to a research project.”

The next step, the scientists say, is a larger study in monkeys, and they’ve alrady begun planning a future study in women volunteers.

Schlievert said there’s evidence that GML also may help prevent other sexually-transmitted diseases, such as chlamydia, as well as other types of infections.

In theory, he said, women could use the treatment “an hour so before they had sex” to protect themselves from infection.

Eventually, he said, the team hopes to develop a formula that could be used for men or women.

Although GML is widely used commercially, it’s not available in this form. The research team combined it with K-Y Jelly for the experiments, and the university has applied for patents for this new potential use, Schlievert said.