Feline Leukemia Virus (FeLV)

Melissa Boldan, DVM
By Melissa Boldan, DVM on Feb. 6, 2023

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What Is Feline Leukemia Virus (FeLV)?

Feline leukemia virus is a common disease that affects about 2% of cats in the United States. It is spread cat-to-cat and leads to the destruction of the cat’s white blood cells and immune system. This 

leaves them more susceptible to infection, cancer, and death. Widespread vaccination has led to an overall decrease in leukemia cases; however, it remains a major disease in cats who frequent the outdoors.

The leukemia virus attacks the cat’s blood cells by invading tissue that makes up the blood cells, including bone marrow and lymph tissue. Blood cells (red blood cells, white blood cells, and platelets) play an important role in keeping the body supplied with oxygen and nutrients. These cells help fight infections and eliminate waste products. White blood cells are especially important in helping the immune system, and special types of white blood cells are called to action when a cat is fighting an illness.

When a cat is infected with feline leukemia virus, its white blood cells have been compromised and are no longer able to help fight off infections. Various skin, respiratory, and urinary infections can develop without a healthy immune system in place. The affected cat is unable to fight off these infections, leading to a shorter life span. The virus also causes mutations leading to cancer, including lymphoma and lymphosarcoma.

Symptoms of Feline Leukemia Virus (FeLV)

Clinical signs of feline leukemia virus come from the blood cells being attacked. Initially, cats may show little signs of infection until the virus has strengthened and taken over more of their immune system. Over time, clinical signs may become more involved as cats develop cancers secondary to the leukemia virus.

The most common clinical signs of feline leukemia virus are:

  • Pale gums (anemia)

  • Decreased appetite

  • Weight loss

  • Unthrifty coat (poorly groomed, dry, brittle)

  • Inflamed gums and mouth (gingivitis and stomatitis) 

  • Fever

  • Enlarged lymph nodes

  • Chronic diarrhea

  • Chronic skin, eye, respiratory, or urinary tract infections

Causes of Feline Leukemia Virus (FeLV)

FeLV in cats is spread through saliva. It is spread most commonly from those exposed to one another for longer periods of time through mutual grooming, mating, or shared food/water/litter boxes. It may also be spread by bite wounds and from a mother to her kittens through the placenta.

A cat at any age can be infected with feline leukemia virus through exposure. Allowing an unvaccinated cat to be unsupervised while outdoors may expose it to infected cats. Bringing a new cat into the home that has not tested negative for the feline leukemia virus may also spread the disease.

Fortunately, the virus is not very hardy in the environment and can only survive on surfaces for a couple of hours. Transmission usually occurs from direct contact between cats.

Feline leukemia virus is not contagious to people or to other pets, like dogs or rabbits.

How Veterinarians Diagnose Feline Leukemia Virus (FeLV)

Feline leukemia is usually diagnosed by a test that requires a small amount of blood, called an ELISA test. This test is quick and routinely done in veterinary clinics. Your veterinarian may recommend repeating the test if they get a positive result, especially in young cats and kittens. Repeating the test 8 to 12 weeks later helps to confirm if an infection is persistent. Some cat immune systems can eliminate the virus when they are first exposed. About 20 to 30 percent of cats will eliminate the virus successfully when they're first exposed.

FeLV undergoes several stages. In the first stage, infected cats show very little signs of disease as the virus enters their mouths and replicates on their tonsils. A little less than one-third of cats can eliminate the virus in this stage—if their immune system is healthy. For the remaining two-thirds of cats, the virus will spread to the lymph tissue and intestines, leading to shedding of viral particles in the feces in addition to the saliva. In advanced stages of the disease, it infects the bone marrow as well. Once the virus gets into the bone marrow it cannot be cleared and these cats are persistently infected for life.

Treatment of Feline Leukemia Virus (FeLV)

Unfortunately, feline leukemia virus does not have a cure. Affected cats are managed medically by treating any secondary infections that can result from the disease. Cats infected with feline leukemia virus often develop secondary skin, upper respiratory tract, eye, or urinary tract infections due to their immune system being compromised.

Antibiotics may be prescribed to treat any secondary bacterial infections that may be present. Sometimes appetite stimulants or anti-inflammatory medications are prescribed in leukemia cat pet patients who have a poor appetite or fever. Occasionally, blood transfusions may be recommended for continued quality life for cats with severe anemia.

If your cat tests positive for feline leukemia virus, it is important to limit its exposure to secondary infections. It is best that she remains indoors only and does not have access to other cats that may have spreadable diseases. While a simple upper respiratory tract infection may be easily cleared by a healthy cat’s immune system, feline leukemia patients have a compromised immune system and will require more aggressive treatment and earlier intervention with antibiotics. Any illness, no matter how small, is a threat to a compromised immune system.

Recovery and Management of Feline Leukemia Virus (FeLV)

Some cats diagnosed with FeLV can live normal lives for years, especially if they are kept indoors with minimal exposure to secondary illnesses. The average life span after testing positive for leukemia virus is less than three years. If your cat has feline leukemia and is allowed access to the outdoors, be sure it is under supervision. It is also important to prevent any cat interactions, such as fighting. If your cat enjoys the outdoors, but you want to limit its exposure to the elements, consider a catio. Always avoid allowing shared food/water bowls and litter boxes between affected and non-affected cats to reduce risk of transmission.

Management of a cat with feline leukemia may require more frequent cleaning of the eyes and ears to keep them free of debris. Secondary skin, respiratory, eye, ear and urinary tracts can be common in cats with compromised immune systems, so it’s helpful to keep them clean. Commercial ear cleaners, like Epi-Otic or Epi-Klean, can be used to clean out any waxy debris in the ear canals. Eye washes can be helpful in keeping the eyes clear.

Regular brushing will keep the skin and coat healthy. If any signs of infection are noted, such as green-yellowish drainage in the eyes or nose, lethargy, decreased appetite, cough, increased urination, or inflammation in the ears, schedule an appointment with your veterinarian as soon as possible. Often, vets tend to be more proactive with antibiotics in a cat that has feline leukemia, since its immune system is not as robust.

Prevention of Feline Leukemia Virus (FeLV)

You can reduce your cat’s risk of contracting feline leukemia with regular vaccination. It is recommended that cats who spend any time outdoors—or cats that have exposure to potentially infected cats—get an annual vaccination. The American Association of Feline Practitioners recommends all kittens be vaccinated within their first year. Young kittens start the vaccine series at 8 weeks of age and receive a booster 3 to 4 weeks later. Cats at-risk should continue regular vaccination each year, while low risk indoor-only cats may discontinue the vaccine after the initial series. Vaccinated cats will not test positive on feline leukemia snap tests.

If a cat tests positive for feline leukemia, it should not be vaccinated, as it puts excess strain on its immune system. Any new cat should be tested for feline leukemia and FIV prior to being introduced to other cats in the household.

Feline Leukemia Virus (FeLV) FAQs

Is feline leukemia fatal?

Feline leukemia virus is a fatal disease; however, many infected cats can live for several years with good quality of life.


  • Cornell Veterinary Health Center. Feline Leukemia Virus. 2016..

  • Legendre, A. DVM 360. Feline Leukemia Virus. 2009.

  • Teller, L. Today’s Veterinary Practice. Feline Leukemia Virus Vaccination. 2021.

Featured Image: iStock.com/Hanna Taniukevich


Melissa Boldan, DVM


Melissa Boldan, DVM


Dr. Melissa Boldan graduated from the University of Missouri College of Veterinary Medicine in 2012. She initially practiced mixed animal...

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