Feline leukemia virus (FeLV) is one of the most common and destructive of all cat viruses. It is highly contagious and is spread primarily by saliva during cat fights or mating. In cats living in close contact for long periods, the virus may spread through grooming of one another. The virus may also spread by contact with infected blood and urine. Kittens may become infected while still in the womb, at birth when the mother bites off the umbilical cord, or during nursing.
Not all cats exposed to FeLV become permanently infected. In about 60% of exposed cats, the immune system destroys or inactivates the invading virus. Approximately 30% of exposed cats become persistently infected, and in 10% the virus becomes dormant (inactive) in some area of the body. In this last group, the virus may later become active if the cat is given certain drugs, is severely stressed, or develops another disease.
Of the cats that become persistently infected (30%), about 50% die within 6 months of diagnosis and 80% die within 3 years. While the remaining 20% may live a normal lifespan, they tend to suffer a variety of chronic illnesses.
There is no single group of signs characteristic of FeLV infection. The virus tends to damage the body in one of three ways: an uncontrolled increase of virus-altered body cells that causes tumors or leukemia of the red, white, or bone marrow cells; destruction of parent or immature blood cells that results in severely decreased numbers of the cells essential for blood clotting or red or white blood cells; or dysfunction of the immune system, resulting in life-threatening infections.
Diseases commonly associated with FeLV infection include anemia, cancer, chronic respiratory disease, chronic infection of the mouth and gums, chronic eye disease, chronic skin disease, urinary tract infections, chronic digestive tract disorders, reproductive diseases (abortions, stillbirths, kitten deaths) and other systemic diseases, such as feline infectious peritonitis, feline immunodeficiency virus infection, and toxoplasmosis.
Vaccination before exposure to the virus is the best means of preventing FeLV infection. Without vaccination, isolation from other cats is the only means of prevention.
• Infected cats are at high risk for developing cancer or other life-threatening disease.
• While outdoor cats are at high risk for developing FeLV infection, indoor cats are at low risk.
• There is no uniformly effective treatment for cats infected with FeLV.