Feline leukemia virus (FeLV) is one of the most important infectious diseases of cats worldwide. Affected cats can develop anemia (a low red blood cell level), cancers, and/or suppression of the immune system. The disease worsens over time and is usually fatal. The virus can infect domestic and wild cats (such as lions). Widespread testing and vaccination efforts have helped to reduce the prevalence of the disease over the past 30 years, and in 2010 approximately 3% of the cats in the United States were infected. There is increased risk for the disease among outdoor cats, unneutered males, and cats with other diseases (especially respiratory disease, mouth diseases, and abscesses).
Feline leukemia virus is transmitted between cats via infected saliva and urine. Direct contact with these body fluids, mutual grooming, shared litter boxes and food dishes, and fighting (bite wounds) all expose uninfected cats to the virus. To become infected, cats typically require prolonged, repeated exposure to the virus. Mother cats can also transmit the virus to their kittens while they are in the womb and through breast milk. It is likely that the transmission from a mother to her kittens is the greatest source of infection. Young kittens have the highest risk for catching the virus, whereas adults may have some inherent protection. However, cats of all ages can catch the virus and develop the disease.
Cats infected by feline leukemia virus can develop a number of different disorders, including:
cancer (especially lymphoma and leukemia)
suppression of the immune system (increasing the risk of other infections)
immune-mediated disease (in which the cat's immune system causes damage to its own cells)
reproductive problems (loss of pregnancy and "fading kitten" syndrome)
intestinal inflammation, neurologic disorders (including nerve dysfunction and blindness)
stomatitis (severe inflammation in the mouth)
These disorders can be worsened by the presence of other infectious diseases, such as feline panleukopenia or calicivirus.
Feline leukemia virus is diagnosed with a quick blood test. Your veterinarian may recommend the test when you first adopt your cat, before vaccinating against the disease, after exposure to the virus (for example, after a cat bite wound), or if your cat is ill. The test may need to be repeated in 30 days if the risk of infection is high. If your cat goes outside or lives with another cat that has the virus, your veterinarian may recommend that the test be repeated every year. Additional laboratory tests may be necessary if your cat tests positive for the virus.
Unfortunately, there is no cure for feline leukemia virus. Some positive cats can live without major complications for years with routine veterinary care, proper feeding and care, minimal stress, and avoidance of secondary infections. Infected cats should be kept strictly indoors to reduce the risk of other infections and to prevent spreading the virus to other cats. Your cat should visit the veterinarian at least every 6 months to monitor for disease-related disorders and secondary infections. Your veterinarian will make a recommendation for appropriate vaccinations against other feline viruses (vaccination for FeLV will not help once a cat is infected with the virus). All infected cats should be neutered. See your veterinarian immediately if you notice any sign of infection or illness, because treatments should be started as soon as possible.
Feline leukemia virus is usually ultimately fatal. but infected cats may still have a good quality of life. The average survival time after diagnosis is 2.4 years, but some cats will appear "healthy" for multiple years. The disease typically develops faster in kittens than in adults, and some adults ultimately succumb to unrelated conditions.
A vaccine is available to prevent feline leukemia virus infection. Your veterinarian will tell you whether it is appropriate for your cat. The virus does not spread to people.