Feline Leukemia Virus (FeLV) is one fo the most common and destructive of all cat viruses.  It is highly contagious and is spread primarily by saliva during cat fights, grooming or mating.  The virus is also spread by blood, urine and feces.  Kittens may become infected while still in the womb, when the mother bites off the umbilical cord or during nursing.

Not all cats exposed to FeLV become infected.  About 40% of exposed cats have immune systems that destroy the invading virus.  The remainder of exposed cats become persistently infected (30%) or develop a latent infection (30%).  The latter group has inactive virus in their bone marrow, and these virus particles may later become active when the cat becomes ill from another disease, stress or certain drugs.

Of the cats persistently infected, about 25% will die within 1 year and 75% will die within 3 years.  Some may live a normal life but tend to have various chronic illnesses.


There are no signs specific for FeLV infection.  The main effect of the virus is to disrupt the cat’s immune system.  While anemia is the most common disorder caused by the virus, cancer and various other diseases are common.  Disorders commonly associated with FeLV infection include: chronic respiratory disease; chronic infection of the mouth, gums and tongue; chronic eye disease; frequent or chronic skin disease; reproductive disease; frequent or chronic urinary tract infections; chronic digestive tract disease; and other systemic diseases.


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.  Indoor cats are at low risk for developing FeLV, while outdoor cats are at a much higher risk.