Feline Leukemia Virus – When and Why Should We Vaccinate?

The Feline leukemia virus vaccine is a non-core vaccine in Canada, meaning it is not one of the mandatory vaccinations required for your cat at vaccinations. It is however recommended by vets, especially for kittens and outdoor cats and is boosted yearly to provide protection against disease for those cats at risk of infection.

What is Feline Leukemia, and what does it cause?
Feline leukemia virus (FeLV) is one of the most common infectious diseases in cats, although its prevalence is decreasing thanks to vaccination and blood testing.
It is a viral infection that can result in a number of different disease processes.

  • Neoplasia – FeLV is one of the most common causes of cancer in cats, damaging DNA resulting in blood tumours such as lymphoma and leukemias. FeLV cats are 50x more likely to develop lymphomas than non-infected cats.
  • Immunosuppression – FeLV suppresses a cat’s immune system, predisposing them to infections due to weakened immune response. These infections are responsible for many of the FeLV related diseases seen in infected cats.
  • Anemia – various blood disorders develop from FeLV due to suppressing blood formation in the bone marrow.
  • Other diseases – FeLV can cause numerous other disorders including skin disease, arthritis, intestinal problems, neurological signs and reproductive failure (infertility, abortion).

Feline Leukemia Virus Symptoms
Immunosuppression is the main cause of clinical symptoms in cats infected with FeLV. During the early stages of infection, a cat may exhibit little to no symptoms of a disease, however over time they may show signs of recurrent or long term illnesses with the cat’s health deteriorating.

Signs can include:

  • Loss of appetite
  • Progressive weight loss
  • Lethargy
  • Poor coat condition
  • Persistent fever
  • Pale gums
  • Enlarged lymph nodes
  • Inflammation of gums and mouth
  • Persistent diarrhea
  • Skin, urinary and respiratory infections
  • Eye problems
  • Abortion/reproductive failure in females

How do cats get Feline Leukemia Virus?
Cats that are persistently infected with FeLV act as a source of infection for other cats. The virus is shed in saliva, nasal secretions, feces, urine and milk of infected cats. It is contagious and spread in numerous ways, including:

  • Mutual grooming
  • Bite wounds
  • Nursing (mother to a kitten)
  • Shared litter boxes (rarely)
  • In utero (passed from infected mother to kittens during pregnancy)
  • It does not survive long in the environment, only persisting for a few hours in a household environment.

How is FeLV Diagnosed?
Blood tests are available to test your cat for FeLV. It is heavily recommended for any new cat to be screened for FeLV infection before entering a household as well as any cat showing clinical signs of FeLV sharing a household with a FeLV-infected cat.

So why is it important to vaccinate against Feline Leukemia Virus?
There is no cure for FeLV, and it is usually fatal.
Cats most at risk of FeLV infection are those who are exposed to infected cats and kittens.

  • Outdoor cats have an increased risk as they may encounter cats with unknown FeLV status.
  • Kittens are especially at risk as they are much more susceptible to infection than adult cats and can be exposed to the infection through nursing as well as grooming and bites.
  • Cats that live with FeLV positive cats are also at an increased risk.

Vaccination Recommendations
All kittens should be vaccinated at their initial round of vaccines, usually at 12 and 16 weeks of age.
This is then boosted yearly to maintain immunity.
Yearly boosters are recommended for outdoor cats and those interacting with other cats or known FeLV infected cats.

Written by: Dr. Jenni Bartlett, BVM&S MRCVS

Feline leukemia virus (FeLV) | International Cat Care. (2017). Retrieved 27 September 2019, from https://icatcare.org/advice/cat-health/feline-leukaemia-virus-felv
Feline Leukemia Virus. (2019). Retrieved 27 September 2019, from https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/feline-leukemia-virus
Feline Leukemia Virus (FeLV) – Cat Owners – Veterinary Manual. (2019). Retrieved 27 September 2019, from https://www.merckvetmanual.com/cat-owners/disorders-affecting-multiple-body-systems-of-cats/feline-leukemia-virus-felv
Feline Leukemia Virus and Related Diseases in Cats – Overview – Generalized Conditions – Veterinary Manual. (2019). Retrieved 27 September 2019, from https://www.merckvetmanual.com/generalized-conditions/feline-leukemia-virus-and-related-diseases/feline-leukemia-virus-and-related-diseases-in-cats-overview
Younghusband, T. (2019). Feline Leukaemia Virus: a guide for cat owners – The Village News. Retrieved 27 September 2019, from https://thevillagenews.co.za/feline-leukaemia-virus-a-guide-for-cat-owners/



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Last updated: December 16, 2020

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Thank you for choosing Seneca Animal Clinic for your pets' veterinary needs. As we continue to adjust to the "new normal," we have implemented new protocols to keep you and our team safe.

It is still preferred that you stay in your vehicle while we bring your pet in for their appointment. However, as of August 14, 2020, we will be allowing one client to accompany their pet during their visit for urgent, new puppy/kitten, or euthanasia appointments.

Should you choose to come in with your pet, we kindly ask that you comply with the following protocols:

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