Cats and Leukemia Virus Infection (FeLV)

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Feline Leukemia Virus Infection (FeLV) in Cats

Feline leukemia virus (FeLV) is a disease that impairs the cat’s immune system and causes certain types of cancer. This virus is responsible for a majority of deaths in household cats, affecting all breeds. Males are more likely to contract the infection than females, and it is usually seen between the ages of one to six years old.

Symptoms and Types

Signs depend on the type of infection: FeLV-A, FeLV-B, or FeLV-C. Cats found with the virus can be infected with one, two, or all three types.


  • Occurs in all cats infected with FeLV. It severely weakens the immune system (immunosuppression).


  • Occurs in about 50 percent of FeLV-infected cats, and causes tumors and other abnormal tissue growths.


  • The least common type, occurring in about 1 percent of FeLV-infected cats. It causes severe anemia.

Of these types, some of the more common symptoms include:

  • Anemia
  • Lethargy
  • Weight loss
  • Abscesses
  • Enlarged lymph nodes
  • Persistent diarrhea
  • Infections of the external ear and skin
  • Fever (seen in about 50 percent of cases)
  • Wobbly, uncoordinated or drunken-appearing gait or movement
  • Inflammation of the nose, the cornea, or the moist tissues of the eye
  • Inflammation of the gums and/or mouth tissues
  • Lymphoma (the most common FeLV-associated cancer)
  • Fibrosarcomas (cancer that develops from fibrous tissue)


FeLV is usually contracted from cat-to-cat transmission (e.g., bites, close contact, grooming, and sharing dishes or litter pans). It can also be transmitted to a kitten at birth or through the mother’s milk. Kittens are much more susceptible to the virus, as are males and cats which are allowed to go outside.


Your veterinarian will first rule out other infections such as bacterial, parasitic, viral, or fungal. In addition, nonviral cancers need to be ruled out.

A complete blood count is done to determine if the cat has anemia or other blood disorders. Diagnosis may also be determined by conducting a urinalysis, or through a bone marrow biopsy or bone marrow aspiration (removing a small amount of marrow fluid for study).


Your veterinarian will prescribe medication to treat the symptoms and causes for FeLV. After that, a yearly vaccination for respiratory and intestinal viruses is recommended. Your cat will not be hospitalized unless it has severe secondary infections, low red-blood cell count or extreme weight loss with muscle loss. In these cases, it will be kept under hospital care until its condition stabilizes. Emergency treatment, such as blood transfusions, is sometimes needed.

Opportunistic infections are another concern. These are infections that occur indirectly because of the animal’s weakened immune system (due to the FeLV). Supportive therapy, such as fluids or nutritional supplements, are helpful in these cases.

Diarrhea, kidney disease, or long-term (chronic) muscle loss may require a special diet. Also, infected teeth or gums must be cleaned; teeth extraction is necessary in severe cases.

Living and Management

You will need to monitor your cat for symptoms of infection and keep in touch with the veterinarian regarding follow-up treatment and testing. More than 50 percent of cats that persistently have FeLV in their blood (known as FeLV viremic cats) succumb to related diseases within two to three years after infection.

Keep FeLV-infected cats indoors and separated from healthy cats to prevent the spread of the disease. Good nutrition is important, as is controlling any secondary bacterial, viral, or parasitic infections.


Keeping infected cats separated (and quarantining them) is the only way to prevent FeLV in healthy cats. There are several commercial vaccines for the disease available. However, test the cat before initial vaccination, as it may already be infected.

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