Feline Leukemia Virus (FeLV) is associated with illness in, and death of, more cats than any other infectious agent. Feline Leukemia Virus and Feline Immunodeficiency Virus (FIV) infection occurs worldwide in cats, with prevalence varying by location. Ideally, all cats should be tested for infection with Feline Leukemia Virus and Feline Immunodeficiency Virus.

While there is currently no vaccine available to prevent FIV, one to prevent FeLV infection has been available for many years. It is recommended that those cats at risk of exposure to cats carrying FeLV infection receive the vaccine. However, the most effective way to prevent FeLV infection, and the only way at the present time to prevent FIV infection, is to prevent exposure to infected cats. Testing to identify infected cats serves as the mainstay of preventing viral transmission.

Cats infected with FeLV or FIV may live for many years. A decision for euthanasia should never be made solely on the basis of whether or not a cat is infected. No single test is 100% accurate at all times and under all conditions. A confirmed positive test result should be considered only an indication of retrovirus infection, not clinical disease. And remember, illness in cats infected with FeLV or FIV may not necessarily be a result of retrovirus infection.