FeLV Basics

What is Feline Leukemia (FeLV)?

Feline leukemia virus (FeLV) is a retrovirus that infects cats. FeLV can be transmitted from an infected cat to a non-infected cat mainly through mating but also potentially by way of saliva or nasal secretions. This disease is often referred to as the "licking disease." If not defeated by the animal’s immune system, the virus can shorten their lifespan. 

How is FeLV spread?

By far, the main way the virus is transmitted is through mating.  Once cats are spayed or neutered, the chance of transmission drops greatly. Cat-to-cat transfer of the virus may occur from a bite wound, during mutual grooming, and rarely through the shared use of litter boxes and feeding dishes. Transmission can also take place from an infected mother cat to her kittens, either before they are born or while they are nursing. FeLV doesn't survive long outside a cat's body, dying quickly, usually in less than a few minutes.

What does FeLV do to a cat?

The Feline Leukemia virus weakens the cat's immune system that hinders its ability to protect itself against other infections. Once the leukemia is activated in the bone marrow, it generally shows up in one of several ways:

  • Severe non-regenerative anemia

  • White cells that are not healthy and cannot fight off infection

  • Cancerous growths on key organs (kidneys, liver or intestines) or chest masses that make breathing difficult

  • Cancerous external growths

How is FeLV diagnosed?

Initial screening in a vet’s office with a “snap test” or ELISA test indicates the presence of a protein in the cat’s blood.  This protein often is a false positive when a cat has a severe infection (not FeLV related) and after healing will test negative.  This test may only tell that the cat has been exposed to the FeLV virus, not that they have been infected with it, meaning it is in their bone marrow. Kittens can acquire the virus from their mothers but often by 4-6 months of age, they can fight it off.  In our experience, roughly 30-40% of the snap or ELISA tests are false positive results.

Since the snap test is only a first indicator of possible infection, to verify that a cat is truly infected with FeLV, we require the Quantitative PCR test which tells us that the virus is in the bone marrow.  This test is available from the major vet labs and takes 3-5 days to come back from the lab.  From the Idexx lab, the test numbers are 26354 or 26355.

How long do FeLV-infected cats live?

It is impossible to accurately predict the life expectancy of a cat infected with FeLV.  Kittens are often challenged to live to their first birthday because of weakened immune systems.  Cats that acquire the virus through mating often live longer since their immune system was stronger prior to infection. 

We have learned that home environments with less stress can help FeLV kitties to live longer.  Many misconceptions exist that FeLV infected cats and kittens will become sick soon after diagnosis and this is simply not the case as our experience shows.

Can I give a non-infected cat the FeLV virus after touching an infected kitty?

Feline leukemia virus will not survive outside the cat for more than a few minutes and washing hands after touching a kitty with the virus should keep you from giving it to a healthy kitty. If an infected kitty sneezes or drools on you or your clothing, washing your clothes is recommended.

Is there a vaccine to protect non-FeLV kitties?

FeLV kitties can live with non-FeLV kitties as long as they are up-to-date on their FeLV vaccine.  One vaccine, the Merck Nobivac Feline 2-FeLV vaccine is 92-96% effective in protecting non-FeLV kitties once the cat has had the initial vaccine and the booster in 3-4 weeks. The vaccine is also good for two years. Please consult a veterinarian about vaccines to protect non-FeLV cats.

Can people or animals get FeLV?

FeLV cannot be transmitted from infected cats to humans or other animals. It is unique to cats.