The global HIV epidemic continues to expand, with more than 40 million people now estimated to have the AIDS virus, but in some countries prevention efforts are finally starting to pay off, the United Nations says.

AIDS has killed more than 25 million people since it was first recognized in 1981, making it one of the most destructive epidemics in history. An estimated 3.1 million people died from the virus last year and another 4.9 million people became infected, according to a U.N. update published Monday.

The deaths and new infection estimates were in line with those from last year, when the total number of people living with the virus was estimated at 39.4 million.

However, for the first time there is solid evidence that increased efforts to combat the disease over the last five years have led to fewer new infections in some places, said UNAIDS chief Peter Piot.

Previously, improvements had been seen in places such as Senegal, Uganda and Thailand, but those were rare exceptions.

"Now we have Kenya, several of the Caribbean countries and Zimbabwe with a decline," Piot said, adding that Zimbabwe is the first place in Southern Africa, the hardest-hit area, to show improvement.

These are all countries that have invested heavily in safe-sex campaigns and other prevention programs, with the result that prevalence of HIV among the young has declined.

"People are starting later with their first sexual intercourse, they are having fewer partners, there's more condom use," Piot said.

The epidemic also appears to be tapering off in other countries. "We see similar trends in countries in East Africa, but the evidence was not good enough to put in the report," he said.

The most dramatic drops in prevalence have been among pregnant women in urban Kenya, where in some areas the proportion of pregnant women infected plummeted from approximately 28 percent in 1999 to 9 percent in 2003.

In the Caribbean, declines are evident in Barbados, the Bahamas and Bermuda, Piot said.

In Zimbabwe HIV prevalence among pregnant women in the capital Harare has decreased from 35 percent in 1999 to 21 percent in 2004.

"I absolutely believe we are on a roll," added Dr. Jim Kim, HIV chief at the World Health Organization. "Everyone is sort of jumping on the bandwagon. I think there's been a fundamental change, even in the past one year, in all the efforts in HIV."

There's a new energy, Kim said, and much of that comes from the recent availability of HIV treatment in the developing world.

About 1 million HIV patients in the developing world now are on treatment. While that is just a small fraction of the people needing treatment, the availability of drugs has meant that people see a point to getting tested for the virus, which is crucial for prevention efforts. About 300,000 deaths were avoided last year because of treatment, the report said.

"As much as possible, we've got to get that energy into prevention as well," Kim said.

So far this year the world has spent slightly more than $8 billion on tackling HIV in the developing world. That was a big increase from the $6 billion spent last year but was still far short of the need.

UNAIDS estimates that $9 billion will be spent next year but say $15 billion will be needed.

The epidemics continue to intensify in southern Africa. Growing epidemics are under way in Eastern Europe and in Central and East Asia. Five years ago, one in 10 new infections were in Asia. Today the number is one in four or five.

China, Papua New Guinea and Vietnam are facing significant increases. There are also alarming signs that Pakistan and Indonesia could be on the verge of serious epidemics, the report said.

Intravenous drug use and commercial sex are fueling the epidemic in Asia, where few countries are doing enough to inform people about the danger of such behavior, the report warned.

Worldwide, less than one in five people at risk of becoming infected with HIV has access to basic prevention services. Of people living with HIV only one in 10 has been tested and knows that he or she is infected.