The result of a new nine-year study published in Nature magazine show that assumption to be wrong. A group of scientists led by Beatrice Hahn at the University of Alabama at Birmingham carried out a study of a chimpanzee population in Gombe National Park in Tanzania. They found out that 9-18% of the apes carried SIV. Infected adults were 10-16 times more likely to die than those without the virus. All infants with SIV died, the study says.

Both symptoms of the disease shown by many infected animals and autopsy results resembled those of humans affected by AIDS. For instance, chimpanzees had an abnormally low level of a specific type of immune cell – the CD4 T cell – the same cell type that human immunodeficiency virus targets and destroys.

“From an evolutionary and epidemiological point of view, these data can be regarded as a ‘missing link’ in the history of the HIV pandemic,” said Daniel Douek of the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland.

Hahn says previous assumptions of chimps being able to control SIV similar to some other primates like sooty mangabeys, who have been proven to have this ability, was based on scarce data. “Really, we were making the assumption on very little data. I guess it’s the arrogance of humans thinking all monkeys are the same,” she said.