Feline Leukemia Virus (FeLV)

FeLV is one of the most common viral diseases seen in domestic cats, especially in stray cats. Most commonly, cats are infected at a young age. Typically two scenarios with infected cats are seen. In the first case, kittens get very sick within a few months of becoming infected and die. Those kittens that survive this initial phase tend to have close to normal lives. Since the virus impacts their immune system, they are more susceptible to infections, but tend to be able to recover. As they get older, they are predisposed to other diseases, especially cancer. Lymphoma is the most common cancer seen in FeLV positive cats.

FeLV is most commonly transmitted through the saliva with bites or from even casual contact such as mutual grooming and drinking from the same water source. It can also be transmitted to fetuses in utero, through milk to nursing kittens, or through urine. If a young cat tests positive, it is typically recommended to retest in a few months to confirm he or she is still positive. Sometimes, such as with a low virus exposure, the cat is able to clear the virus. Adult cats tend to have a more natural immunity to the virus, but are still at risk of developing FeLV if exposed to a positive cat.

Any cat new to a household should be tested for FeLV, ideally before being introduced to other cats within the household. An effective vaccine is available against FeLV. It is given by a different route (transdermally) than most vaccines (subcutaneously) to reach immune cells within the skin itself and to decrease the chance of developing an injection-site sarcoma in the future. This vaccine is typically given to cats that go outdoors, or ones in households that foster cats or are exposed to numerous other cats. It is given as a series of 2 vaccines separated by 3 to 4 weeks. It is then repeated annually.

Feline Immunodeficiency Virus (FIV)

FIV is another viral disease found in domestic cats, especially stray cats. It is usually spread by more aggressive contact via saliva—typically bite wounds. Therefore, intact male cats are the most commonly infected. It can also be spread to fetuses in utero and nursing neonates.

Similar to HIV in humans, FIV affects the immune system of infected cats. These cats are predisposed to other diseases, including respiratory disease, gastrointestinal disease, and cancer (especially lymphoma). FIV cannot be spread to humans.

Similar to FeLV, all new cats to a household should be tested for FIV before introducing them to other cats. The test for FIV is looking for antibodies (proteins that develop after the cat is exposed to the virus), not for the virus itself. These antibodies can cross through the placenta during pregnancy and stay in a young kitten’s bloodstream for up to 6 months. Therefore, a young kitten can have a false positive test result. Positive tests should be repeated once the kitten is over 12 months old to see if they remain positive.

There is a vaccine available for FIV, but it has not proven to be effective, and therefore is not offered. Vaccinated cats will have positive test results.