Scientists have discovered that chimpanzees in Tanzania are falling ill and dying from an AIDS-like disease -- a surprising finding that could lead to insights into the illness and, perhaps, to a vaccine.
The study, published in Thursday's edition of the British research journal Nature, showed that chimps infected by certain strains of simian immunodeficiency virus, a precursor to HIV, died 10 to 16 times more frequently than uninfected chimps during a nine-year study.
The results contradict previous evidence suggesting that chimpanzees were immune from AIDS and that SIV infections in the species were harmless.
Researchers already knew that some wild chimpanzees were infected with SIV from eating infected monkeys. A strain of SIV at some point mutated to human immunodeficiency virus in wild chimps in West Africa, where it had jumped to humans who ate infected chimp meat.
AIDS researchers say the discovery presents a unique opportunity to deduce how the closely related SIV and HIV cause disease in closely related species -- chimps and humans. That should speed up development of more effective AIDS therapies and vaccines, researchers say.
"It is a pretty momentous study," said Danny Douek, chief of the human immunology section of the National Institutes of Health vaccine research center in Bethesda, Md.
"You can regard the study as one that provides a missing link in the history of the HIV pandemic," said Douek, who is searching for possible AIDS vaccines and was not part of the Tanzania project. "If we identify the evolutionary adaptations, that opens up therapeutic avenues for HIV disease."
The chimps in the study, from Tanzania's Gombe National Park, are the same animals that scientists have followed since famous primatologist Jane Goodall began watching them in 1960. The 94 Gombe chimps, living in two groups, are habituated to human researchers in their forest home, a key to the study's success.
The primary research was conducted at the University of Alabama at Birmingham, but it relied on the work of two scientists at Chicago's Lincoln Park Zoo: Elizabeth Lonsdorf, director of primate research, and epidemiologist Dominic Travis. The pair set up a survey in 2004 to assess the overall health of the Gombe chimps.
They trained Gombe park biologists to gather data by following animals at least once a month, taking notes on behavioral cues for possible illness or injury, and gathering fecal and urine samples.
The samples were analyzed by the University of Illinois veterinary medical school's pathology department in Chicago. The pathologists trained park veterinarians in Gombe to do field necropsies when a chimp died, taking tissue and fluid samples from the carcasses for analysis in Chicago.
The health survey dovetailed with another project at Gombe by Beatrice Hahn, an AIDS researcher at the University of Alabama at Birmingham. Hahn, who pioneered research into the origins of HIV and how it jumped from chimps to humans, has led a consortium of scientists studying SIV-infected Gombe chimps since 2000.
Pathologist Karen Terio in Chicago was the first to see evidence of the SIV disease process in the chimps from necropsy samples she examined. The tissue in one dead chimp, she said, "looked just like a sample from a human patient who has died of AIDS."
"I couldn't quite believe what I was seeing in the microscope," Terio said. "So I had colleagues confirm it and then immediately got on the phone to tell Lonsdorf and Hahn."