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Research on an AIDS-like disease in monkeys continues to help scientists understand problems such as how HIV causes AIDS, how the virus "hides" from the immune system and how the disease might be prevented or treated, two decades after the human and monkey diseases were identified.

"These animals have been indispensable for understanding how the virus works and in working toward vaccines," said Murray Gardner, professor emeritus of medical pathology at the аÄÃÅÁùºÏ²ÊÄÚÄ»ÐÅÏ¢ Davis Center for Comparative Medicine.

About 300 researchers from around the world will reflect on those past achievements and discuss new data when they gather Sept. 8-11 in Monterey, Calif., for the 20th Annual Symposium on Nonhuman Primate Models for AIDS. The California National Primate Research Center (CNPRC) at the University of California, Davis, is hosting the conference.

More than 20 years ago, scientists at the аÄÃÅÁùºÏ²ÊÄÚÄ»ÐÅÏ¢ Davis primate center were confronted with a mysterious and deadly outbreak of infections in their monkeys. Showing signs of weakened immune systems, the monkeys were succumbing to a variety of infections that normally did not cause disease.

At about the same time, a deadly new disease known as AIDS was making the headlines. Bearing a striking resemblance to the monkey syndrome, the human disease also led to opportunistic infections, wasting and death.

Scientists would later discover that the monkey disease, called simian AIDS, was caused by the simian immunodeficiency virus (SIV), a close relative of the human immunodeficiency virus (HIV) that causes human AIDS.

The striking similarities between the human and simian disorders and the viruses that cause them enabled scientists to gain otherwise unobtainable insights into the origins and progression of human AIDS -- work that continues today.

Today, scientists at the аÄÃÅÁùºÏ²ÊÄÚÄ»ÐÅÏ¢ Davis center are using the SIV monkey model of AIDS to study ways to vaccinate against HIV transmission from adult to adult and from mother to offspring. They are also tackling the problem of eliminating latent virus -- virus that is inactive and "hiding" inside cells in the body -- in individuals taking medications to fight the virus. Finally, they are testing the ability of microbicides to prevent sexual transmission of SIV/HIV.

"The monkey disease is a remarkably accurate facsimile of the human disease," said Gardner.

An authority on retroviruses and the intersection of the simian and human immunodeficiency viruses, Gardner will give the keynote address at the conference, highlighting important contributions of nonhuman primate research to knowledge of AIDS.

According to Gardner, some of the key achievements made by researchers studying immunodeficiency viruses in monkeys include: gaining an in-depth knowledge of the natural history of both the human and simian AIDS viruses, including the potential for and mechanisms of cross-species transmission; demonstrating the feasibility of an AIDS vaccine by showing that monkeys became resistant to simian AIDS when injected with weakened versions of the virus; demonstrating that SIV alone, rather than environmental or other factors, causes simian AIDS; defining the mechanisms of HIV/SIV transmission between hosts; and identifying the role of antibodies and cellular immunity, especially CD8 cells -- a specific immune system component -- in fighting the virus.

The symposium traces its origins to 1983, when about 30 researchers from the then seven U.S. primate research centers met at Tulane University to discuss what was then a poorly understood, spontaneously occurring immunodeficiency syndrome of macaque monkeys. The monkey disease had many strong similarities to AIDS, which was first described in 1981. HIV was first identified in 1983 and SIV in 1985.

Gardner said the founders of the primate centers could never have imagined that monkeys, specifically the Asian rhesus macaque, would play such a critical role in fighting the global AIDS pandemic. Over the past 20 years, AIDS has sickened or killed nearly 40 million people. An estimated 68 million people will have died as a result of AIDS by 2020.

Today, more than half of the research done at the federally funded primate research centers is AIDS-related. In fact, directors of the primate centers maintain they are unable to meet the demand for monkeys for AIDS research and other work because of limited resources. The recent focus on bioterrorism research has further strained an already tight supply.

The National Institutes of Health created the primate centers in 1962 to provide resources and facilities for various regions around the country for biomedical research requiring the use of nonhuman primates. An eighth center, the Southwest National Primate Research Center, was added in 1999. NIH recently gave all the centers a national designation, reflecting their expanded role in addressing biomedical issues in the national interest.

For more information on the symposium, see .