Feline immunodeficiency virus (FIV) was first discovered in 1986 in a California cattery where some cats appeared to have an illness similar to AIDS (acquired immunodeficiency syndrome) in people. Since then, FIV has been discovered in every country that has tested cats for its presence. It appears likely that FIV has been present in cats for many years. The rate of infection varies from about 1% (in healthy cats) to as high as 14% (in ill cats) in Canada and the United States. FIV is often found in cats that are positive for the feline leukemia virus. On average, 2-4% of cats in the United States are infected with FIV. FIV belongs to the same family of viruses as HIV (human immunodeficiency virus) and immunodeficiency viruses in other species. This family of viruses (Lentiviruses) is known for being species-specific, for life-long infection, and for slowly progressive diseases. FIV is not transmissible from cats to people, and HIV is not transmissible to from people to cats.