The first evidence of the clinical disease of Acquired Immune Deficiency Syndrome (AIDS) in an animal infected with the human immunodeficiency virus (HIV-1) was presented by Yerkes Primate Research Center scientist Frank Novembre at the Conference on Retroviruses and Opportunistic Infections on Jan. 30 in Washington, D.C.
A detailed description of the research history and clinical status of the animal, a chimpanzee, is currently being prepared for publication. Since the conference was covered by many reporters, Novembre's presentation about the first animal with AIDS made headlines throughout the country.
The chimpanzee, named Jerom, was experimentally infected with HIV-1, the infectious agent responsible for AIDS in humans, more than 10 years ago in a research study conducted by scientists at Yerkes and the U.S. Centers for Disease Control and Prevention (CDC).
The animal with AIDS is one of 13 chimpanzees at the center that were inoculated with HIV-1 as part of research to develop a primate model for research on this disease or as part of vaccine studies. Several other research centers have conducted similar investigations with chimpanzees, and the total number of chimpanzees that have been infected with HIV-1 as part of vaccine, drug and other research studies on AIDS at these five centers is estimated to be 100. Jerom was the first of these 100 chimpanzees to develop clinical indications of AIDS.
Novembre and Chief of Yerkes Research Resources Harold McClure point out that a chimpanzee developing AIDS as a result of HIV infection supports the case that HIV is the cause of AIDS in humans, referring to the few scientists who have contended that AIDS is not caused by this virus. This finding also strengthens the value of these primates for use in the evaluation of experimental vaccines to protect people against AIDS and for certain other research studies on AIDS.
The use of chimpanzees in many types of AIDS research, however, likely will be limited by the relatively long latency period -- the time between infection and onset of disease -- that has characterized Jerom and that is typical in many people who are infected with HIV-1.
Yerkes scientists have initiated studies to determine whether the HIV isolate from the chimpanzee with AIDS can infect and induce disease in pigtailed macaque monkeys. "The availability of a more readily available, less expensive monkey model for HIV-1 infection would be an extremely important animal model system for studies of the pathogenesis of HIV-1 induced disease as well as for the evaluation of AIDS drugs and vaccines," said McClure, who heads the Yerkes studies related to AIDS.
Although Jerom became persistently infected with HIV--his immune system produced antibodies against the virus, and the virus was isolated repeatedly from samples of his blood--clinical signs of AIDS did not occur until late summer of 1995.
Although he is not yet receiving AZT or other anti-viral drugs that are used to treat people with HIV, Yerkes veterinarians have been treating Jerom when clinical complications that may cause him discomfort have occurred, said McClure. In addition to receiving extensive care from Yerkes veterinarians, Jerom also has been the focus of a great deal of personal attention from the center's primate caretakers and the center's behavioral scientist, who is in charge of enrichment of the laboratory animals' environment, McClure added.
Like many people with AIDS, Jerom has developed several clinical problems associated with the HIV infection. These include: chronic diarrhea with intermittent episodes of severe, acute diarrhea; severe thrombocytopenia, which is a low number of platelets; a cough and a low-grade pneumonia and anemia.
Of particular importance, Jerom's CD4+ cells--which are infection-fighting cells of the immune system--have declined progressively over the past few years and are currently at critically low levels. Such progressive, severe declines in CD4+ cells are a "classic marker" of AIDS in people, said Novembre.
As part of the study, Nathan, one of the 13 chimpanzees in the original AIDS research group, received a blood tranfusion from Jerom. While Nathan has not developed clinical indications of AIDS, his CD4+ cells dramatically declined after exposure to Jerom's blood. The group of 13 will remain the core of the AIDS research efforts with chimpanzees since there are no immediate plans to infect additional chimpanzees.
-- Cathy Yarbrough