Feline Leukemia Virus: What You Need To Know

May 31, 2018
cat health
feline leukemia virus

If you have a cat, chances are that you have heard of feline leukemia virus (FeLV). Maybe your cat has been vaccinated against this virus; maybe your cat has been tested for the virus at some time; or maybe you have been unlucky enough to lose a cat to this serious viral infection. Whatever your experiences, if you have a cat, it is important to understand this virus and why your cat needs to be protected.

What is Feline Leukemia Virus?

FeLV causes lymphoma and leukemia. It is also capable of causing bone marrow disease leading to anemia and immune suppression. As a result, infected cats are more vulnerable to other infections and diseases that healthy cats are better able to fight.

Feline Leukemia Virus infects 3 to 14% of cats worldwide. In Canada, a 2011 survey revealed that about 4.3% of domestic cats tested positive for the virus.

Is my cat at risk?

The virus is transmitted through saliva, feces, urine, and milk from infected cats. Kittens that are under 16 weeks of age are very susceptible to infection.3 It is readily spread between cats that live in sustained close contact, through food and water bowls, litter boxes, and mutual grooming. It can be spread through bite wounds from infected cats. New cats coming into the household pose an infection risk.

Is testing available to diagnose infection?

A screening test is available that detects the presence of viral protein in the blood. If a cat is positive for this test, additional tests may need to be run to confirm infection.

Who should be tested?

All new cats coming into a household and all kittens should be tested for FeLV. Cats that roam outdoors should be tested annually, and cats that have interacted with new cats since their last test should be tested again. Sick cats should be tested, regardless of prior test results. The need for testing should be evaluated regularly by your veterinarian, based on your cat’s risk of exposure.

What can I do to protect my cat?

Vaccinations against FeLV provide excellent protection. All young cats should be vaccinated against FeLV. Outdoor cats, or cats that come into contact with new cats regularly, should also be vaccinated. Cats that live with FeLV-infected cats should be tested for FeLV infection and if negative, vaccinated against the virus. New cats coming into a household should be tested prior to introducing them to existing cats.

Feline leukemia virus is an insidious infectious agent that can complicate a cat’s health severely, and eventually lead to death. While testing is available to detect infected cats, there are no specific treatments available. As such, vaccinating and identifying infected cats to prevent infection remains the most successful means of protecting cats from this virus.


1. Burling AN, Levy JK, Scott HM, et al. (2017). Seroprevalences of feline leukemia virus and feline immunodeficiency virus infection in cats in the United States and Canada and risk factors for seropositivity. J Am Vet Med Assoc251 (2):187-194.

2. Little S. Bienzle D, Carioto L et al. (2011). Feline leukemia virus and feline immunodeficiency virus in Canada: Recommendations for testing and management. CVJ: 52 (8); 849-855.

3. Grant CK, Essex M, Gardner MB and Hardy WD, Jr. (1980). Natural feline leukemia virus infection and the immune response of cats of different agesCancer Res40: 823–829.

This article was sponsored by Boehringer Ingelheim Animal Health and written by feline specialist Kelly St. Denis, MSc, DVM, DABVP of Charing Cross Cat Clinic, Brantford, ON.

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