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Feline Leukemia Virus Infection



•  A retrovirus that causes inability to develop a normal immune response (known as “immunodeficiency”) and development of tumors in domestic cats


•  No genetic susceptibility to infection by feline leukemia virus (FeLV)


•  Cats

Breed Predilections

•  None

Mean Age and Range

•  Number of cases highest between 1 and 6 years of age

•  Mean—3 years of age

Predominant Sex

•  Male-to-female ratio—1.7:1 (that is, males are 1.7 times more likely to have feline leukemia virus infection than are females)

Signs/Observed Changes in the Pet

•  Onset of feline leukemia virus–associated disease—usually occurs over a period of months to years after infection

•  Associated diseases—may be related to inability to develop a normal immune response (immunodeficiency) or to development of tumors or cancer

•  Clinical signs of FeLV-induced inability to develop a normal immune response (immunodeficiency) cannot be distinguished from those of feline immunodeficiency virus (FIV)-induced immunodeficiency

•  Signs depend on the type of disease (inability to develop a normal immune response [immunodeficiency] or tumor/cancer) and occurrence of secondary infections

•  Enlarged lymph nodes (known as “lymphadenomegaly”)—mild to severe

•  Upper respiratory tract disease—inflammation of the nose (known as “rhinitis”), inflammation of the moist tissues of the eye (known as “conjunctivitis”), and inflammation of the cornea (known as “keratitis”; the “cornea” is the is the clear outer layer of the front of the eye), seen in 18% of cases

•  Persistent diarrhea

•  Inflammation of the gums (known as “gingivitis”), of the mouth (known as “stomatitis”), and/or of the tissues surrounding and supporting the teeth (known as “periodontitis”)

•  Long-term (chronic), nonresponsive or recurrent infections of the external ear and skin; abscesses

•  Fever and wasting (seen in 42% to 53% of cases)

•  Lymphoma (a type of cancer that develops from lymphoid tissue, including lymphocytes, a type of white-blood cell formed in lymphatic tissues throughout the body)—most common FeLV-associated cancer

•  Leukemia

•  Fibrosarcomas (cancer that develops from fibrous tissue)—in pets co-infected with mutated sarcoma virus; most frequently in young cats

•  Disorders usually affecting the nerves to the legs and paws (known as “peripheral neuropathies”); progressive wobbly, incoordinated or “drunken” appearing gait or movement (known as “ataxia”)


•  Cat-to-cat transmission—bites; close casual contact (such as grooming); shared dishes or litter pans

•  Transmission of the virus from the mother cat (known as a “queen”) around the time of birth—fetal and newborn kitten death from 80% of affected queens; transmission across the placenta or through the milk in at least 20% of surviving kittens from infected queens

Risk Factors

•  Age—kittens are much more susceptible to infection than are adults

•  Male—result of behavior

•  Cat allowed outside; free-roaming cats

•  Multicat household


Health Care

•  Outpatient for most cats

•  Inpatient—may be required with severe secondary infections, low red-blood cell count (known as “anemia”), or extreme weight loss with muscle wasting (known as “cachexia”) until condition is stable

•  Blood transfusions—emergency support; multiple transfusions may be necessary

•  Management of secondary and opportunistic infections—primary consideration; “opportunistic infections” are infections caused by organisms that usually do not cause disease, but are able to cause disease because the cat’s body and/or immune system has been weakened, in this case by the feline leukemia virus infection

•  Supportive therapy (such as fluids and nutritional supplements) may be useful


•  Normal


•  Normal

•  Diarrhea, kidney disease, or long-term (chronic) wasting—may require special diet


•  Biopsy or surgical removal of tumors

•  Dental cleaning, tooth extraction, biopsy of the gums


Medications presented in this section are intended to provide general information about possible treatment. The treatment for a particular condition may evolve as medical advances are made; therefore, the medications should not be considered as all inclusive

•  Zidovudine (Retrovir)—antiviral agent; may lead to clinical improvement, but does not clear virus

•  Medications to alter the immune response (known as “immunomodulatory drugs”)—may alleviate some clinical signs; interferon (Roferon) may increase survival rates and improve clinical status; Propionibacterium acnes (ImmunoRegulin); acemannan (Carrisyn)

•  Mycoplasma haemofelis infection—suspect in all cats with low red-blood cell counts due to the destruction of red-blood cells, in which the body is producing new red-blood cells (known as “regenerative hemolytic anemia”); oxytetracycline or doxycycline; short-term use of steroids, administered by mouth, if needed

•  Lymphoma (a type of cancer that develops from lymphoid tissue, including lymphocytes, a type of white-blood cell formed in lymphatic tissues throughout the body)—management with standard combination chemotherapy protocols; periods of remission average 3–4 months; some cats may remain in remission for much longer

•  Blood disorders or disease and leukemias—less responsive to medical treatment; for low red-blood cell count (anemia), try erythropoietin (Epogen); for low neutrophil count (known as “neutropenia”), try Neupogen

•  Yearly vaccination for respiratory and intestinal viruses with inactivated vaccines recommended

Follow-Up Care

Patient Monitoring

•  Varies according to the secondary infections and other manifestations of disease

Preventions and Avoidance

•  Prevent contact with feline leukemia virus–-positive cats

•  Quarantine and test incoming cats before introduction into households currently with one or more cats


•  Several commercial feline leukemia virus vaccines are available

•  Test cats for FeLV before initial vaccination; if prevaccination testing is not done, advise clients that the cat may already be infected

•  Vaccinate kittens at 8–9 weeks and 12 weeks of age; administer booster FeLV vaccine at 1 year of age; revaccinate every 2–3 years thereafter

Possible Complications

•  Exposure of non-feline leukemia virus–infected cats to infection

•  Development of disease related to inability to develop a normal immune response (immunodeficiency)

•  Development of tumors or cancer

•  Death

Expected Course and Prognosis

•  Cats that persistently have feline leukemia virus in their blood (known as “FeLV viremic cats”)—more than 50% succumb to related diseases within 2–3 years after infection

Key Points

•  Keep feline leukemia virus–infected cats indoors and separated from FeLV-negative cats, to protect them from exposure to secondary disease-causing agents and to prevent spread of FeLV to other cats

•  Good nutrition is important

•  Control secondary bacterial, viral, and parasitic infections




Blackwell’s Five-Minute Veterinary Consult: Canine and Feline, Fifth Edition, Larry P. Tilley and Francis W.K. Smith, Jr. © 2011 John Wiley & Sons, Inc.