Feline Leukemia Virus Infection


Feline leukemia virus (also known as FeLV ) is a special type of virus called a retrovirus. After infection, retroviruses change their genes (i.e. their genetic makeup) to match the infected animal's genes. This allows the retrovirus to become part of the infected animal's DNA, and in most cases, remain in the animal for the duration of his or her life.

FeLV in cats is spread mostly through contact with saliva, but can also be spread from:

  • Blood

  • Tears

  • Urine

  • Feces

  • Nasal discharge

  • Milk

  • Unborn kittens

Common causes of spread include:

  • Sharing food and water bowls

  • Sharing litterboxes with infected cats

  • Infected cats grooming non-infected cats

Only feline species (e.g. cats) can be infected with FeLV.

Feline leukemia virus infection tends to affect organs and blood cells that are associated with the immune system. This can lead to a weakened immune system, causing pets to struggle to fight off illnesses (e.g. respiratory tract infections) or to come down with illnesses and diseases more frequently than healthy cats.

Symptoms and Identification

Feline leukemia virus symptoms vary quite a bit depending on how the cat's immune system handles the virus. Some cats do not show any symptoms. Other cats will only show symptoms during or after stress or other illnesses. Still others may only show symptoms of poor healing or increased numbers of other types of infections compared to healthy cats. In other words, FeLV-infected cats are not sick all the time, so it may be difficult to tell that they are infected.

Common symptoms seen in sick cats with FeLV include:

  • Fever

  • Weight loss

  • Not wanting to move around

  • Acting tired

  • Poor appetite

  • Pale skin and gums

  • Enlarged lymph nodes (which appear as lumps under the skin)

  • Squinting and eye redness

  • Painful

  • Red gums (also known as gingivostomatitis)

  • Diarrhea or loose stool

  • Runny nose and eyes

Cats with FeLV are prone to cancer such as leukemia or lymphoma, so masses/tumors may also be noted in cats showing symptoms.

Many veterinary clinics have tests for FeLV that can be performed in the clinic. Results take about 10 minutes, and they are usually pretty accurate. Infected cats are referred to as FeLV-positive cats. Sometimes additional testing needs to be sent off to confirm the results, or the in-clinic test needs to be performed again in 60 days. If cancer is also suspected, biopsy or additional lab testing may also be needed. If the pet has very severe symptoms of illness, additional lab work and X-rays may be required to assess how the internal organs and immune system are handling the illness.

Affected Breeds

No specific breeds are predisposed to FeLV infection, but some research has shown that male cats are more prone to infection than females.


No cure exists for FeLV infection, and many infected cats remain infected for life. Some antiviral treatments have been studied and may be helpful for cats who only show symptoms after stress/other illness. However, these treatments have not been studied in great detail, so it is unclear how effective they really are.

Because FeLV infection decreases the body's ability to fight infections, the primary means of treatment is through managing or preventing other illnesses that occur because of FeLV. As soon as an FeLV-positive cat begins to act sick (e.g. sneezing, coughing, diarrhea, trouble urinating, etc.), they need to be taken to the vet for care. The sooner an illness can be addressed, the less likely it will be to become severe or drawn out.

Long-term, FeLV-infected cats may have a shorter lifespan than non-infected cats, but it depends on many factors. Overall, cats with FeLV can live a good quality of life if infections can be managed well and they can be kept healthy.

Veterinary Cost

Cost depends on how sick the pet is. In-clinic testing ranges from $60-120. Confirmation tests at an outside laboratory may range from $150-300. Yearly veterinary costs for FeLV-positive cats will likely be increased compared to non-infected cats because of an increased risk for other infections. Yearly cost above vaccines and other preventives may range from $150-600 depending on how sick the cat becomes with other illnesses.


Feline leukemia virus vaccines can help prevent infection. They are not 100% effective, but studies have shown that being previously vaccinated definitely lowers the risk of FeLV infection.

The American Association of Feline Practitioners (AAFP) currently recommends that all kittens one year of age or younger be vaccinated for FeLV. Cats at high risk for FeLV, such as those that spend time outdoors or those who live with an FeLV-positive housemate, should be vaccinated yearly. Cats at lower risk for infection can potentially be vaccinated every 2-3 years.

Non-infected cats in the household can be further protected from FeLV-positive housemates by separating them if possible. At a minimum for cats that can't be separated, use individual litter boxes and food and water bowls and clean and disinfect surfaces routinely. As cats age, they become less likely to become infected. However, FeLV infection can still happen in older cats, so caution is always warranted.


1. Hartmann K: Feline Leukemia Virus Infection. Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis, 2006 pp. 105-129.

2. Hartmann K: Update on Management and Treatment of Feline Leukemia Virus-Infected Cats. ACVIM 2007.

3. Colleran EJ: Feline Retrovirus Updates. Atlantic Coast Veterinary Conference 2017.

4. Little S, Levy J, Hartmann K, et al: 2020 AAFP Feline Retrovirus Testing and Management Guidelines. J Feline Med Surg 2020 Vol 22 (1) pp. 5-30.

5. Cattori V, Randon R, Riond B, et al: The kinetics of feline leukaemia virus shedding in experimentally infected cats are associated with infection outcome. Vet Microbiol 2009 Vol 133 (3) pp. 292-296.

6. Yoshino Y, Chambers JK, Nakamori T, et al: Primary cerebellar lymphoma with Hodgkin lymphoma-like morphology in a cat. J Vet Diagn Invest 2017 Vol 29 (5) pp. 707-710.

7. de Miranda L H, Meli M, Conceicao-Silva F, et al: Co-infection with feline retrovirus is related to changes in immunological parameters of cats with sporotrichosis. PLoS One 2018 Vol 13 (1) pp. e0207644.

8. Gruffydd-Jones T: Update On Testing For Feline Retroviruses. World Small Animal Veterinary Association World Congress Proceedings 2009.

9. Levy J, Frenden M, Hamman N: FeLV: What You Need to Know for Shelter Decision Making. American Pets Alive! Conference 2019.

10. Buch JS, Clark GH, Cahill R, et al: Analytical validation of a reference laboratory ELISA for the detection of feline leukemia virus p27 antigen. J Vet Diagn Invest 2017 Vol 29 (5) pp. 654-659.