Epidemiologic and clinical aspects of feline immunodeficiency virus infection in cats from the continental United States and Canada and possible mode of transmission

Summary The epidemiologic features of feline immunodeficiency virus (fiv) infection were evaluated in 2,765 cats from the United States and Canada. Of these cats, 2,254 were considered by veterinarians to be at high risk for the infection, and 511 were healthy cats considered to be at low or unknown risk. Of the cats in the high-risk group, 318 (14%) were found to be infected with fiv. The infection rate among low- or unknown-risk cats was 6 of 511 (1.2%). Male cats in the high-risk group were 3 times more likely to be infected than were females, similarly as were cats >6 years old, compared with younger cats; domestic cats, compared with purebred cats; and free-roaming cats, compared with confined cats. Feline immunodeficiency virus and FeLV infections did not appear to be linked with each other; 16% of FeLV-infected cats in the high- and low-risk groups were coinfected with fiv. In contrast, there was a pronounced linkage between fiv and feline syncytium-forming virus (FeSFV) infections. Seventy-four percent of FeSFV-infected cats in the high-risk study group were coinfected with fiv, compared with a 38% fiv infection rate among cats that were not infected with FeSFV. The major clinical manifestations associated with fiv infection in cats that were surveyed included chronic oral cavity infections (56%), chronic upper respiratory tract disease (34%), chronic enteritis (19%), and chronic conjunctivitis (11%). Bacterial infections of the urinary tract (cystitis), skin, and ears were seen in a small proportion of cats. Fever of unspecified origin, anorexia, weight loss, lethargy, vomiting, abnormal behavioral problems, lymphosarcoma, and myeloproliferative disorders were seen as accompanying or primary features of the disease in a proportion of affected cats. Anemia and leukopenia were observed in about a third of the cats that were clinically ill at the time of testing. Experimental studies indicated that biting was a highly efficient mode of transmission. Cats with clinical signs of illness tended to shed more virus in their saliva than did healthy carrier cats. Seroepidemiologic studies also supported the notion that territorial aggression and biting were important natural modes of fiv transmission. A group of 18 human beings who had intimate contact with fiv-infected cats were found to be seronegative for the virus. There was no positive evidence that fiv was of public health importance.