Feline Leukemia Virus (FeLV)


Feline leukemia virus is a retrovirus that infects cats. FeLV can be transmitted between infected cats when the transfer of saliva or nasal secretions is involved. If not defeated by the animal’s immune system, the virus can be lethal. A disease caused by this virus is a form of cancer of the blood cells called lymphocytes (a type of leukemia).  While proper care provided by a veterinarian can extend, and in many instances increase the quality of life of an infected cat, there is currently no known cure.

Signs and Symptoms

The signs and symptoms of infection with feline leukemia virus are quite varied and include loss of appetite, poor coat condition, anisocoria (uneven pupils), infections of the skin, bladder and respiratory tract, oral disease, seizures, lymphadenopathy (swollen lymph nodes), skin lesions, fatigue, fever, weight loss, stomatitis (inflammation of the mucous lining of the mouth, gums or lips), gingivitis, litter box avoidance, pancytopenia (a reduction in the blood cell count and platelets), poor grooming, recurring bacterial and viral illnesses, anemia, diarrhea, and jaundice.


Cats infected with FeLV can serve as sources of infection. They can pass the virus between each other through saliva and close contact, by biting another cat, through a litter box or food dish used by an infected cat, and from milk during nursing. Transmission can take place from an infected mother cat to her kittens, either before they are born or while they are nursing. It is estimated that most transmissions of FeLV occur via saliva and friendly behaviors, such as nursing, sharing feeding bowls and mutual grooming (as distinct from fighting and biting).

FeLV causes immunosuppression in domestic cats, but there is also credible evidence for its existence of the virus in larger wild cat populations (e.g. lynx, cheetahs, and lions).  On the other hand, overwhelming epidemiologic evidence suggests FeLV is not transmissible to either humans or dogs.  In fact, there is apparently no canine version of this disease at all.  It is not known to infect non-feline species.

Because of their immature immune systems, young kittens are more susceptible to infection, but by 8 months of age become somewhat resistant.  They can also be born with it, having contracted it from their mother while in utero.


Vaccines are very effective and the best means of prevention.  Although no FeLV vaccine provides perfect protection, the overwhelming majority of veterinarians recommend vaccination.

Since the virus is very weak and dies within two hours in a dry environment, the incidence of transmission will drop considerably if the litter box is kept from remaining damp between uses in multi-cat households. One method is to clean all damp litter out of a standard box after each use; however, this is sometimes not practical.

Another option is a specialized three-part litter box that uses either a ground corncob or safflower seed litter in a slotted top unit, which allows the liquid to drain into a reservoir that is emptied regularly. The litter material air-dries quickly, thus killing the virus. This litter box was originally designed for diabetic cats to allow regular testing of the sugar level in the cat’s system. Coincidentally, the box was also found to help reduce the chances of FeLV transmission between household cats.