A volatile mix of emerging and established risks threatens to transform Asia's current HIV/Aids epidemic into a full-blown pandemic in the near future. A dangerous sense of complacency and a deeply ingrained social stigma surrounding the disease are major stumbling blocks to stemming its spread. But most alarming: Governments are neglecting the major breeding grounds for HIV/Aids -- drug users and commercial sex workers.

As Aids experts and activists converge on Bangkok for an International Aids Conference on July 11-18, a just-released 18-month study compiled by the Asian Development Bank and UNAIDS, a special body set up to coordinate the United Nation's response to Aids, concludes that it is "make or break" time for Asia. More than 7 million people currently live with HIV/Aids in the Asia-Pacific region. HIV/Aids causes around 500,000 deaths per year. The cost to Asia: around $7.3 billion in 2001, according to the report.

As long as Asia stays in denial, those costs will rise. If governments fail to substantially increase spending on HIV/Aids-prevention programmes and on care and treatment for sufferers, the costs will add up to 10 million new infections, 750,000 annual deaths and an estimated $17.5 billion in associated financial losses per year by 2010, according to the report.

"Asian governments need to act now," says Swarup Sarkar, one of the report's researchers. "Every country runs the risk of being grossly under-resourced."

HIV/Aids activists and experts hope that the Bangkok conference, which will be attended by heads of government as well as global experts, will sound the alarm in Asia. Already millions of people have been impoverished by HIV/Aids there. And the cost of inaction on the region's society and economy is growing as the epidemic matures and HIV hits people in their prime.

It was once hoped that Asia would escape the kind of Aids scourge that has devastated large parts of Africa, where prevalence rates can be as high as 40%. But public-health experts warn that complacency and denial are covering up a huge danger to the region, which now accounts for one in five new HIV infections worldwide. "We're still dealing with new epidemics and the old ones are still ongoing," says Dr. Chris Beyrer, director of the Johns Hopkins Fogarty Aids International Training and Research Programme in Baltimore in the United States.

Because of Asia's massive population, plain percentage comparisons with sub-Saharan Africa mask the huge human toll of HIV/Aids in the region. Consider the world's two most-populous nations: India has 4.58 million people living with HIV -- that's second only to South Africa, which has an estimated 5 million cases. And in China, where official estimates put the number of infections at less than 1 million, the ADB/UNAIDS report warns that the number could reach 10 million by 2010 without more aggressive action.

For Asia's larger populations, a small increase in prevalence rates can substantially boost total numbers. Notes Beyrer: "3% or 4% of an adult population living with a fatal disease is a disastrous epidemic."

Asia is wealthier than sub-Saharan Africa, where the horror of Aids is conveyed by the haunting pictures of its orphans. But Beyrer, who has worked on Aids issues in Asia, argues that from the perspective of epidemiology, Asia's story is still unfolding -- and it is tending to follow a pattern well-established in the West.

Take the case of Indonesia, where as recently as a decade ago, there were virtually no Aids cases. Today, Southeast Asia's most-populous country, with around 216 million people, faces a surging epidemic stemming from an alarming rise in intravenous drug users.

Indonesia is an example of how swiftly an Aids epidemic can erupt and spread. A 1996-97 study of some 800 commercial sex workers in Jakarta conducted by a U.S. Navy medical team found that not one was infected with HIV. They were looking in the wrong place. In 2002 the Indonesian authorities estimated that among 160,000 intravenous drug users, 85% were sharing needles, and half of them are believed to be infected with HIV.

Aids epidemics in Europe and the U.S. spread rapidly among drug users, says Nick Crofts, a professor and director of the Centre for Harm Reduction at the Macfarlane Burnet Institute for Medical research and Public Health in Melbourne, Australia. They catch HIV using dirty needles; then they pass the disease along to commercial sex workers. "The epidemic among drug users feeds a sexual epidemic," he says.

While countries such as Thailand have trumpeted success in reducing heterosexual transmission of HIV through safe-sex campaigns, many governments tend to ignore or deny the existence of other risk groups at the core of their epidemics -- like the estimated 4.5 million injecting-drug users across Asia. In Thailand, for example, the 2003 crackdown on drug dealers has forced many drug addicts into hiding and inhibited proper epidemiological surveillance of the problem. Hong Kong is one of the few places in Asia with an effective provision of clean needles for addicts.

The trouble is that the number of intravenous-drug users is on the rise in Asia. "The economic crisis in 1997 gave the drug trade a huge boost," says Crofts, with more people turning to the habit as an escape or as a means of making money. Patterns of drugs exports from places like Burma and Pakistan have changed with rising demand, with smuggling by sea to avoid crackdowns along their land borders.

Ironically, there are also dangers stemming from success in combating the disease. In Thailand, which was credited with reducing infection rates through its HIV-prevention campaigns, complacency is creeping in. The government is spending less on prevention -- activists say it has not paid enough attention to the stubbornly steady number of infections among drug users, and the safe-sex message that was once loud and clear is now failing to reach some sex workers.

Consider Bombuey, a Thai teenager with long bangs that shroud her face and obscure the dark circles under her eyes that are a sign that she has full-blown Aids. "Where you from?" she asks a visitor in bar-girl English. When asked how she is feeling, Bombuey flits off with a practiced prance. Bombuey is over her tuberculosis, says Father Joe Maier, the director of the Aids hospice in Bangkok where she has been treated. "In a couple of weeks she'll be back in the bars of Phuket for a last hurrah," he says. "She'll give a few people Aids. Then she'll come back to die."

Thoughts are divided over how to tackle the Aids challenge in Asia. Institutions like UNAIDS and the ADB favour throwing money at the problem, even while many countries' public-health systems are ill-equipped to efficiently disburse and target big budgets.

They say if governments take action now, new infections by 2010 can be brought down from an expected 10 million to 4 million, saving the region $2 billion annually in the process. The new report stresses that as the epidemic evolves, governments will need to secure and spend $5.1 billion each year from 2007 to 2010 to contain its spread, representing a massive increase from the current level of $200 million Asia's governments now spend.

Smaller non-governmental organizations prefer a more nuanced, less costly approach. Some experts say it's best to focus on specific behaviour that's causing the most infections. That's the tack advocated by an international network of epidemiologists and public-health professionals in a group called Monitoring the Aids Pandemic Network, which will issue a report making that case in mid-July.

One of the authors, Elizabeth Pisani, is an epidemiologist with Family Health International's Asia regional office. "We know how HIV is spread in Asia and we know what to do about it," she says. In her view, a massive focus on providing clean needles for drug addicts and condoms for sex workers will reduce the likelihood of epidemics spreading beyond the high-risk populations. "Most Asians do not engage in behaviours that put them at risk for HIV. It is critical that we focus our prevention efforts on providing condoms and clean needles to the minority who do."

The trouble is that the people catching HIV in Asia are mostly on the margins of society and often on the move. This poses problems for treatment with more readily available antiretroviral drugs. Treatments with these drugs must be taken rigorously and under medical supervision; they are not suited for drug users living unstable lives, points out Crofts. What's more, he says, "poor compliance with ARV treatment can promote the rise of drug-resistant strains of HIV."

It's also hard to persuade governments to counsel drug dealers and commercial sex workers where a strong social stigma makes it tough to recognize the problem. If a drug user in Nepal can find a needle to share in a public toilet, or an Indonesian addict can seek solace in the arms of a streetwalker for less than $10, preventing a full-blown HIV/Aids pandemic in Asia won't be possible without a strong, concerted regional response.