FIV is efficiently transmitted through bite wounds, with virus being shed in the saliva of infected cats. Placental or colostral transmission for FIV from an infected queen to her offspring occurs infrequently. Serologic tests for FIV indicate that the virus is distributed widely throughout North America. Estimated prevalence of FIV infection in the United States is 1.5 to 5 percent in the healthy cat population and 9 to 15 percent in cats exhibiting signs of clinical illness. Restrospective serologic surveys conducted in the United States, Great Britain and Japan indicate that FIV has been well established in the cat population for more than 20 years.
Male cats are approximately three times as likely to be infected as females.
The prevalence of FIV infection increases with age, with average age being about 5 years at the time of diagnosis. When cats are infected with FIV, neutralizing antibodies appear three to four weeks after infection. FIV can be isolated from infected cats in spite of high neutralizing antibody titers. Some cats may have undetectable or weak antibody levels for weeks to months before finally seroconverting. In addition, FIV antibody levels may drop precipitously in some cats during the terminal stages of disease.