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Using biochemical tools that were not available at the beginning of the epidemics in Africa and the Americas, molecular biologist Chin-Yih Ou and his colleagues at the U.S. Centers for Disease Control found two distinct epidemics caused by somewhat different strains of HIV in the northern Thai city of Chiang Mai. Both epidemics started no more than four years ago, but one occurred mostly in intravenous drug abusers and the other started in female prostitutes. There was little overlap between the two groups.
The scientists discovered that the prostitutes were more often infected by a strain resembling those types found in Africa. Apparently, it preferred the moist mucosal tissue of the genital organs, making heterosexual transmission easier. The other variety, found in the drug abusers, appeared similar to strains detected in the U.S. and Europe. It thrived on immune cells in the bloodstream. As a result, transmission occurred through the exchange of contaminated blood, as might occur during the sharing of needles or in abrasive anal sex.
The rise of two or more dissimilar types of HIV could explain why AIDS did not explode among heterosexuals in the U.S. and Europe, yet spread rapidly among men and women in Africa and parts of Asia. HIV has still not evolved in the industrialized world into a form that is easily transmitted by heterosexual activity. But it probably will, given the virus' proven ability to mutate. "Over time, in the U.S., more and more strains will adapt to become more efficient at heterosexual transmission," Essex says. "So far, there haven't been a critical number of people infected heterosexually. As that happens, you will get adaptation of the virus for transmission in that route. The heterosexual epidemic in the U.S. will expand."
Already American physicians are seeing more women with HIV. In many AIDS clinics in San Francisco and New York City, women make up 30% to 50% of all new patients. About half of them became infected through heterosexual contact. They range from very well educated to barely literate, but most of them say | they had no idea that their sexual partners had engaged in high-risk behavior. In fact, because AIDS is still thought of as a gay man's disease in the U.S., many women discover that they are infected only after they have passed the virus on to their children.
Another alarming trend is that more and more AIDS patients are developing tuberculosis. Normally, they respond to the traditional treatments for this degenerative lung disorder. However, a growing number of AIDS patients are contracting a much deadlier form of TB that is resistant to standard drug therapy. In Amsterdam Dr. James Curran, head of the AIDS program at the CDC, called the combination a "double epidemic."
Since the bacteria that cause TB spread through the air, they threaten not only AIDS patients but healthy people as well. Those with an intact immune system can usually fight off the infection, but this does not hold true for people who harbor HIV. Until the resurgence of TB, medical personnel who were HIV-positive but still healthy could work on AIDS floors without jeopardizing their own or anyone else's well-being. Now they will face a greater risk of encountering and developing TB. More AIDS patients are thus likely to be treated under quarantine conditions to avoid spreading the TB bacteria.
Tragically, even as AIDS goes in ever more dangerous demographic directions, government agencies throughout the world are failing to respond. Prevention programs are stalled or being abandoned. The World Health Organization's AIDS budget for this year is $90 million, down from $110 million two years ago. In the U.S., the National Institutes of Health requested $1.2 billion for AIDS in next year's budget, but President Bush trimmed that amount to $873 million and Congress is likely to cut it even further.
By the year 2000 AIDS could become the largest epidemic of the century, eclipsing the influenza scourge of 1918. That disaster killed 20 million people, or 1% of the world's population -- more than twice the number of soldiers who died in World War I. "This epidemic is of historic scale," says June Osborn of the U.S. AIDS commission, "but the response has been far short of historic."
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