Feline Leukemia

Feline leukemia is a disease that is caused by infection with the feline leukemia virus (FELV) that can cause cancer and weaken a cat's immune system, making them extremely susceptible to infections. The virus is transmitted through bite wounds, close contact (e.g., mutual grooming) with an infected cat, or from an infected mother to her offspring. Young cats and pets that go outside or live with an infected housemate are at greatest risk for developing feline leukemia




When a cat is exposed to FELV it may develop an effective immune response and eliminate the virus from its body or become chronically infected. Clinical signs of FELV infection can vary tremendously, but lethargy, inappetence, weight loss, vomiting, diarrhea, oral inflammation, pale mucous membranes, and neurological disorders are all possible. Any sick cat or new addition to a household should be tested for FELV infection with a simple blood test. In some cases, several tests must be run over a period of time or different types of lab work ordered to determine if a cat is truly infected or free from the feline leukemia virus.




Although feline leukemia cannot be cured, diagnosing the disease in an otherwise healthy cat is not an immediate death sentence. Many animals can live perfectly normal lives for many years with FELV, particularly if they are kept inside and any health problems that do develop receive appropriate and prompt treatment. Once a cat becomes sick as a result of FELV infection, its long-term prognosis becomes poor. An FELV vaccine is available and routinely used to help prevent this devastating disease, but serious side effects, including cancer at the injection site, sometimes occur so its use should be restricted to cats at high risk for developing feline leukemia.


Written by: Jennifer Coates, DVM
Last reviewed: October 2, 2008