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Feline Leukemia Virus (FeLV)

Fact Sheet| Veterinarian Awareness

Quick Facts:

  • FeLV is a retrovirus that compromises a cat’s immune system.
  • FeLV is a feline-only virus that cannot be transmitted to humans.
  • Cats who test positive for FeLV can live for many years without serious symptoms.
  • A positive FeLV test result SHOULD NOT be a death sentence.
  • A vaccination for FeLV exists, but it is not 100 percent effective.
  • In rare instances, FeLV can spread through the shared use of litter boxes and/or feeding dishes.
  • A positive FeLV test in a cat is not necessarily a diagnosis. False positives can occur.
  • We strongly recommend against testing community cats for FeLV.
  • Spaying and neutering is key to preventing FeLV spread by minimizing biting behavior that is the main mode of transmission.

Alley Cat Allies is committed to providing cat owners, caregivers, veterinarians, veterinary technicians, policymakers and anyone who cares for cats with the most up-to-date facts about Feline Leukemia Virus (FeLV). We have worked with veterinary experts and advisors for decades to develop best practices and protocols to protect cats who test positive for FeLV.

FeLV is a feline-only virus that cannot be transmitted to humans. It’s important to not confuse FeLV with Feline Immunodeficiency Virus (FIV), though both are species-specific viruses that only affect cats.

Though there is no known cure, FeLV is far from a death sentence. They have weaker immune systems, but cats who test positive for FeLV can live fulfilling and happy lives like any other catsand can live for many years, often without harmful symptoms.

Why is it important to understand FeLV and how it is tested?

Consider this scenario: A cat with no signs of health issues is brought to an animal shelter. Shelter staff conduct a routine FeLV test, and the cat is found positive for FeLV. As a result, the cat is killed. Though she showed no symptoms of FeLV-related health problems, the test was still treated as a life or death matter.

This cat, and many others just like her, could have had a high quality of life in indoor homes with people or outdoors with their feline families. On top of that, the test may have been incorrect. FeLV tests are not diagnoses and can be unreliable for multiple reasons.

Whether you have a cat who has tested positive for FeLV, are trying to decide which tests to include for a Trap-Neuter-Return (TNR) program, or are answering questions from others on FeLV, the information below will help you save lives.

What Is Feline Leukemia Virus (FeLV)?

Feline Leukemia Virus (FeLV) is a retrovirus belonging to the coronavirus subfamily, which means it is a cancer-causing virus. FeLV only affects cats and cannot be spread to humans or other animals.

How Is FeLV Spread?

FeLV is spread primarily through cats’ saliva. It can also spread through blood, tears, feces, and urine.

Most cats get the virus from their infected mothers at birth or through prolonged direct contact with FeLV-positive cats, such as mutual grooming. FeLV also spreads through bite wounds, such as those caused by male cats fighting.

In rare instances, FeLV can spread through the shared use of litter boxes or feeding dishes.

How Can FeLV Transmission Be Prevented?

FeLV cannot survive for more than a few hours outside a cat’s body in most environments and is easily destroyed with soap and water.

Spaying and neutering cats helps prevent FeLV transmission by minimizing biting behavior. When cats are spayed or neutered, hormone-driven fights (and any resulting bites) associated with mating decrease dramatically. Spaying and neutering also ends the transmission of FeLV from mother cats to kittens.

It is important to know that a vaccination for FeLV exists, but it is not 100 percent effective. People should consult their veterinarians and determine their cat’s risk factors for FeLV when deciding whether to vaccinate.

What Happens When a Cat Is Exposed to FeLV?

FeLV can cause severe anemia and suppress the immune system, leaving the cat vulnerable to a variety of opportunistic diseases.

FeLV Stages

One of three things can happen once a cat contracts FeLV:

1. Abortive Infection and Immunity

The cat may experience a transient viral infection, fight off the virus, and develop future immunity. Kittens younger than 16 weeks old are much less likely to fight off FeLV than adult cats.

2. Progressive Infection and Disease

If the initial FeLV infection is not overcome, the virus replicates and the kitten or cat becomes persistently infected. The virus eventually moves to the bone marrow and compromises the immune system. Although a cat in this state may show no signs of illness for several years, FeLV-related diseases such as anemia, skin diseases, and leukemia typically develop within two to three years. Cats with progressive FeLV infection shed the virus in their bodily secretions (including saliva) and can infect other cats.

3. Regressive Infection and Immunity

Cats who become persistently infected do not always develop disease as a result. Some cats produce an effective immune response to the virus while continuing to harbor the virus in their bodies. This results in a regressive or carrier statean FeLV-infected cat who has low risk of developing FeLV-related diseases. The regressive phase of FeLV infection seems to be temporary for most cats. They can actually become free of the virus within a few years. Cats in the regressive infection state are unlikely to shed or spread FeLV.

Unlike cats with progressive infections, cats with regressive infection of FeLV almost never shed or spread the virus. They do not infect other cats unless through a blood transfusion done by a veterinarian.

What are the Symptoms of FeLV?

Signs that a cat has FeLV include:

  • Loss of appetite
  • Weight loss
  • Poor coat condition
  • Persistent fever
  • Inflammation of the gums and mouth
  • Skin, urinary, and upper respiratory tract infections
  • Persistent diarrhea
  • Seizures, behavior changes, and other neurological disorders
  • A variety of eye conditions

It is important to note that many of these symptoms may not be related to FeLV at all.

Other conditions FeLV can cause include:

  • Leukemia
  • Lymphoma
  • Infertility

How Does FeLV Testing Work?

Usually, cats are initially tested for FeLV with a point-of-care (POC) test, meaning they are tested at a veterinary clinic or shelter. This test, also called an ELISA (enzyme-linked immunosorbent assay) test, provides a quick diagnosis during the same visit in which the cat is tested. FeLV POC tests are best run on a cat’s blood rather than saliva.

It can take up to 30 days or more after infection for an infected cat to test positive for FeLV antigens. For the most conclusive results, cats should be retested a month after they were believed to be infectedespecially if they originally tested positive for FeLV.

A positive FeLV test in a cat is not necessarily a diagnosis. Many times, further testing is needed. An FeLV-positive test does not require euthanasia unless the cat is already ill and suffering beyond treatment.

If a cat or kitten tests negative for FeLV:

If the initial ELISA test is negative but you believe the cat was exposed to FeLV, you can have the test redone after 30 days for a more accurate result.

If a cat or kitten tests positive for FeLV:

If the initial ELISA test is positive, a more in-depth test is required to confirm the diagnosis. The veterinarian can send a sample to a laboratory, which will conduct a polymerase chain reaction (PCR) test or an immunofluorescence assay (IFA).

FeLV tests can provide false positives or inconclusive results:

  • A cat in the initial stage of FeLV infection may test negative for FeLV even if they are infected. A cat exposed to FeLV may test positive during the transient phase of the infection and then test negative if the virus is overcome. Overall, results can be shaky and difficult to trust.
  • In general, FeLV tests are not 100 percent accurate and can yield false positive results.

How is FeLV Managed?

Although there is no known cure for FeLV, supportive care can improve the quality of life, health, and longevity of cats with FeLV. An infected cat may live free of FeLV-related disease for her entire lifetime. Any secondary infections and diseases can be treated as they occur.

Some recommendations for supportive care include:

  • Minimizing stress. Consider products like FELIWAY®, which mimics a cat’s natural calming pheromones.
  • Feeding ’em the good stuff. Make sure your cat is getting good nutrition and consult with a veterinarian to determine the healthiest possible food.
  • Being vigilant. Promptly taking cats to the veterinarian when they appear ill is especially important for cats with FeLV. Their weakened immune systems can cause them to contract other diseases or infections more easily. If you watch closely and get them immediate treatment, you can better protect them.
  • Staying up to date. Keep up with the latest information on FeLV in case new treatments or diagnostic developments emerge.
  • Seeking support. Ask for help from fellow caregivers caring for cats with FeLV. You may have someone in your area with lots of experience and helpful advice. Try reaching out to our Feral Friends Network members near you.

What About FeLV in Community Cats?

Alley Cat Allies, informed by the advice of our veterinary experts, strongly recommends against testing community cats for FeLV. Studies show that FeLV is present in community cats at an equally low rate as in owned cats.[1] There is no need for particular concerns about community cats, who thrive in their outdoor homes.

In addition to low rates of FeLV and poor viability of the virus, the cost of testing makes regular community cat FeLV tests irresponsible. Plus, these costly tests can provide inconclusive results. Not only can testing needlessly endanger community cats’ lives if their results are positive, it simply isn’t worth the money spent.

Investing funds in spay and neuter programs like TNR, Shelter-Neuter-Return (SNR) and Return-To-Field (RTF) is a far better way to protect cats outdoors from FeLV. You can find the details in the “How Can FeLV Transmission Be Prevented?” section above

Caregivers can help community cats with FeLV by providing care including:

  • Shelter or a quiet place to rest
  • Good nutrition
  • Swift veterinary services if cats ever appear ill

As of 2020, the American Association of Feline Practitioners (AAFP) Feline Retrovirus Testing and Management Guidelines are now further in line with Alley Cat Allies’ FeLV recommendations.

Read for more information about selection and interpretation of FeLV and FIV tests and suggestions for FeLV-positive cat care from the (AAFP).

Best Practices for Veterinarians and Animal Shelters

A cat who tests positive for FeLV at a veterinary clinic or shelter should not be euthanized unless she is already ill or suffering beyond what can be treated. FeLV testing should be done with a plan to help the cat if she tests positive, not to end her life.

No veterinary hospital or shelter should prohibit a cat who tests positive for FeLV from leaving with her owner or caregiver. People should be allowed to take their cat regardless of test result. If a healthy community cat is brought into a veterinary clinic for spay and neuter as part of Trap-Neuter-Return (TNR), she should not be tested for FeLV at all.

Alley Cat Allies recommends that adoptable cats in shelters be tested for FeLV in-house only if they will be placed for adoption regardless of the result rather than “euthanized.” Shelters can also simply advise adopters to have their new cat tested for FeLV at a veterinary clinic and not test in their facilities at all.

All shelters should implement programs that help find homes for adoptable cats who test positive for FeLV. Many shelters already have model programs that can be used as blueprints.

Additional Resources


[1] “Prevalence of feline leukemia virus infection and serum antibodies against feline immunodeficiency virus is unowned free-roaming cats,” JAVMA, Vol 220, No. 5, March 1, 2002