Feline Leukaemia Virus (FeLV)

Feline leukemia virus, a retrovirus, is a common infection of cats. It is the cause of more cat deaths, directly or indirectly, than any other organism and is widespread in the cat population.

Disease Transmission

Feline leukaemia virus infection (FeLV) can be transmitted several ways:

  1. by the saliva of infected cats contaminating the eye, mouth, and nose membranes of non-infected cats via licking.
  2. by passing infected blood to non-infected cats.
  3. from mother to fetuses (developing kittens) during pregnancy.


Most infected cats eliminate the virus and become immune. In those cats that do not develop immunity, the virus spreads to the bone marrow.

Proliferative and degenerative diseases may occur in any of the tissues invaded by the virus, or the virus may be indirectly responsible for other illnesses because of its immunosuppressive effect. A large percentage of the cats that are exposed to the virus will have latent (hidden) infections and will be capable of transmitting the disease in saliva, tears, and urine. Some of these latent carriers will become clinically ill when stressed.

Diagnostic Tests

Necessary diagnostic tests may include blood chemistry, hematology, radiography, bone marrow aspiration, ophthalmoscopy, and specialized antibody tests.


There is no effective treatment for the myeloproliferative (bone marrow) form of leukemia. Treatment is mainly supportive, and may require blood transfusions and prednisolone.

FeLV cancer (lymphoma) has a better response to therapy than the myeloproliferative diseases do and has the same response to chemo as dolymphoma cases in FELV – cases. Treatment may include chemotherapy,glucocorticoids, interferon, and supportive treatment.


Eighty-five percent of cats with FeLV infection, with 2 positive tests 2 months apart, die within 3 years of the diagnosis.

Prevention of FeLV

There are several preventive measures that can be taken to decrease the risk of contracting FeLV.

  1.  Cats can be FeLV tested, and then vaccinated if they are negative.

Vaccination is strongly recommended for high risk cats. FeLV vaccination of infected cats does not affect the carrier state,

the capacity to infect other cats, or the development of disease in the infected cats. Vaccination may also be associated with adverse events.

(Duration of immunity may vary from fifteen weeks to three years.)

Kittens may be tested at any age. However, infection in newborn kittens may not be detected until weeks to months after birth.

Therefore, several FeLV tests during the first six months of life may be necessary to feel completely “safe” about a negative test result.

All kittens or adult cats that test negative by the first ELISA screening test – but with a known or suspected exposure to FeLV – should be retested. This is done to rule out possible negative results obtained during incubation of the FeLV virus. Although the majority of cats will test positive within several weeks, final retest of negative cats should be no sooner than 90 days post-exposure.

  1. In large catteries, a test and removal program can be instituted.
  1. Multi-cat households with FeLV positive cats should be maintained as a closed colony. (No new cats should be brought into the household, to prevent the spread of infection to the new arrivals.)


Retroviruses are unstable, live for only minutes outside the cat’s body, and are readily destroyed by most disinfectants. Because the feline leukemia virus is so unstable, a new, healthy cat can be brought safely into a “contaminated” house within days of the departure of a FeLV infected cat

Acknowledgement: Becky Lundgren, DVM, Dave Miller MMedvet, BVsc