NEW YORK (CNN/Money) - With nearly 40 million people with AIDS worldwide, why aren't drug companies pouring everything they have into a cure for what some health workers call "the disease of mass destruction?"

"It's not a commercially attractive market," said Barbara Ryan, who follows the industry for Deutsche Bank North America. "The prices [of AIDS drugs] get negotiated down by governments around the world."

The United Nations estimated there were 39.4 million people in 2004 living with the human immunodeficiency virus, which causes AIDS. The UN says that 4.9 million people became infected in 2004 and 3.1 million died, the highest annual tally of fatalities since the first case was diagnosed in 1981.

"Most of the infected people are in Third World countries who can't afford and don't have access to these drugs," said Andrew McDonald, analyst for ThinkEquity Partners.

According to the U.N., 25.4 million AIDS patients, or 64 percent of the world's total, live in sub-Saharan Africa, where poverty is widespread.

"You've got to give product away in Africa," said Ryan, the Deutsche Bank analyst. "There's a natural arbitrage where the prices get pressure around the world."

Geoff Porges, an analyst at the Wall Street research firm Bernstein, said total sales of AIDS drugs worldwide are about $3.5 billion to $4 billion.

Those revenues are divided among the 27 drugs identified by the Food and Drug Administration as AIDS therapies, made by nine different companies.

That compares with annual sales of $4 billion or more for much more profitable drugs that treat high cholesterol, high blood pressure and schizophrenia, among others.

Nonetheless, there are profits to be made on AIDS treatments, especially since marketing costs are low and governments collaborate with private companies on research.

GlaxoSmithKline is the industry leader with eight AIDS drugs on the market. Glaxo (down $0.02 to $48.03, Research) was the first drugmaker to develop an AIDS drug, Retrovir, which has been available since 1987. Bristol-Myers Squibb (down $0.39 to $24.88, Research) is a close competitor with five products on the market.

Glaxo's Combivir, a two-drug AIDS treatment, had more than $1 billion in 2004 sales.

But most of that came from the United States and Europe, where the UN estimates the number of AIDS patients at 1.6 million, about 5 percent of the world total. According to Glaxo, Combivir sales were $512 million in the U.S., $414 million in Europe, and $119 million everywhere else.

"It is not one of the most profitable areas financially but it has certainly been a valuable area of research if you look at what we've been able to do with the disease, going from what used to be a killer disease in the 1980s to what, in the developed world, would be a chronic disease," said Glaxo spokeswoman Mary Anne Rhyne.

"But we've got a long way to go in the developing world."

Rhyne said that "corporate responsibility" and "good public relations" are incentives in developing and marketing AIDS drugs.

"I think we have a corporate responsibility to try and make our medicines available," said Rhyne. "But to stay in business we can't give it away and we can't sell at a loss. We have to sell medicines at a sustainable price."

More AIDS drugs could help drugmakers repair the industry's tarnished image.

Merck, one of the biggest drugmakers with $22.9 billion in sales last year, faces more than 2,300 lawsuits after withdrawing its arthritis painkiller Vioxx from the market last year because of health risks. As a result, Merck stock has tumbled by more than a third over the last year. But the company is considered the market leader for researching a potential AIDS vaccine.

Earlier this year, Merck began phase 2 testing for an AIDS vaccine in conjunction with the HIV Vaccine Trials Network, a non-profit organization. Merck's product is designed to inject synthetic HIV cells into the body, stimulating the production of cells that kill the real HIV. While dozens of other vaccines are in testing, Merck's product is in the most advanced stages of clinical trials.

The importance of an AIDS vaccine cannot be overstated. Since a vaccine would be used as a preventative, the target population is vast. But most of the new cases are in the poorest countries. The UN estimates 13,000 new AIDS cases every day, 95 percent of them in the developing world.

Much of the research for a potential vaccine is funded in part by the federal government's National Institutes of Health. The NIH added $100 million to its 2005 budget for AIDS vaccine research, to $607 million, even though its overall budget for AIDS research increased by only $12 million, to $2.9 billion. The NIH slashed funding in other areas of AIDS research to bolster its vaccine program.

Wayne Koff, senior vice president of research for the International AIDS Vaccine Initiative, said that researching a potential vaccine is like "chasing a moving target" because of the virus' tendency to mutate. But Koff, whose organization funds vaccine research, said the possibility of developing a successful vaccine holds huge implications in fighting the disease.

"A vaccine is the best hope to end the epidemic," said Koff.

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