When the International AIDS Conference opens in Barcelona next week, activists and health experts will focus–rightly–on the calamity at hand. But the current crisis may not be the only one we face. Could this whole nightmare repeat itself? Do our primate relatives harbor other potential AIDS viruses? And are we doing what we can to avoid them? Scientists are now bearing down hard on these questions, and their latest findings are not reassuring. In a recently published study, French and American researchers report finding “a plethora” of genetically varied viruses–all from the same family as HIV–among wild-caught primates in the central African nation of Cameroon. What’s worse, the animals they studied were all in situations where people could have come into contact with their blood. Some were pets, but most were being hunted, butchered and marketed as meat.

This isn’t the first time such viruses have been sighted in the wild. Over the past couple of decades, researchers have identified more than a score of SIVs, or simian immunodeficiency viruses, and plotted out their genetic and evolutionary relationships. They all spread through blood and body fluids and splice themselves permanently into the cells of infected animals. They rarely cause harm when confined to their natural hosts, but they can have catastrophic effects when passed from one primate species into another. Macaques develop AIDS when they contract SIV from sooty mangabeys. So do human beings. In fact HIV-2, a rare AIDS virus confined to West Africa, is essentially a sooty-mangabey virus in a person. HIV-1, for its part, is the near twin of an SIV unique to chimpanzees.

The Cameroon study was an ingenious effort to see whether people are still being exposed to SIV. Blood borne viruses don’t spread through casual contact or the consumption of cooked meat. But hunting, butchering and pet care can all involve exposure to body fluids. So a team led by Dr. Martine Peeters of Montpellier, France, collected and analyzed blood samples from 788 wild monkeys that had been killed for meat or kept as pets. Of the 16 species included in the survey, all but three included SIV-positive animals. The overall infection rate was nearly 20 percent. And in combing through the blood samples, the researchers discovered four strains of SIV that had never been spotted before. There is nothing uniquely dangerous about newly identified viruses. But as Peeters and her colleagues conclude in a report on their findings, “hunters and food handlers may be at risk of infection with many more SIVs than just those from chimpanzees and sooty mangabeys.”

How many SIVs are out there? The study doesn’t answer that question, for it covered only one region of one country, and didn’t even encompass all the local primate species. And no one knows which of the SIVs in nature pose risks to human beings. Many SIVs will infect human cells in a test tube, but that doesn’t mean they could seed human epidemics. “The odds are extremely low,” says Dr. Beatrice Hahn, a University of Alabama researcher who took part in the study. “Cross-species transmission is a rare event.” It’s even rarer for a non human pathogen to spread from person to person. But knowing what huge consequences rare events can have, the researchers are now scrambling to develop a specific and reliable blood test for each of the known SIVs. When those tests are in hand, they’ll start monitoring blood samples from people at high risk of exposure.

Such tests may someday provide the warning we lacked during the formative years of the AIDS pandemic. But the real challenge is to prevent new diseases, not just to recognize them early. Health experts, conservationists and a growing number of lawmakers agree that curbing the bushmeat trade is a critical first step. The killing and handling of primates is an inherently risky business–and as experience has taught us, hunters are not the only ones it endangers. The trouble is, it’s also a booming, profitable enterprise in a region racked by poverty. According to the U.S.-based Bushmeat Crisis Task Force, hunters in central Africa now bag a million metric tons of wildlife every year–and the trade is exploding as logging roads open new areas to commercial exploitation. AIDS may pose more urgent challenges–especially for the 40 million people already infected with HIV. But there is no reason to assume that this is the last such plague we’ll face. The more science reveals about what’s out there, the scarier it looks.