Feline Leukemia Vaccine


Feline Leukemia Virus (FeLV) was one of the leading causes of death in cats until the development of a vaccine in the mid-1980’s.

What is Feline Leukemia Virus (FeLV)?

Feline leukemia virus (FeLV) is one of the most important viruses infecting cats. FeLV tends to become a persistent infection and depresses the immune system of cats. FeLV is an important cause of anemia in cats and can cause cancers of several types.

How common is FeLV?

FeLV infection is found worldwide. Because cats become persistently infected and may carry the virus for long periods before showing any clinical signs, your cat may be exposed to FeLV without you realizing it.

What diseases does the virus cause?

FeLV invades and replicates in various cells of the cat’s immune system and blood-forming tissues, as well as other cells. The immune system becomes suppressed, making the FeLV-infected cat more susceptible to chronic or recurrent infections. Death or dysfunction of infected cells may give rise to enteritis (inflammation of the intestine) or anemia (low red blood cell numbers). FeLV infection can also change the genetic code in infected cells. The genetic code programs the cell’s functions. Changes in genetic code as a result of FeLV infection may eventually give rise to cancers such as leukemia, lymphosarcoma or other tumors. These tumors may affect one or many tissues, organs or body sites.

FeLV is usually fatal. Studies have shown that 80-90% of FeLV-infected cats will die within three to four years of the initial diagnosis.

Is there any treatment for FeLV infection or disease?

There is currently no specific treatment for FeLV-infected cats. Treatment is usually aimed at easing the symptoms and treating secondary infections. Most FeLV-infected cats will eventually die of diseases related to their infection or require euthanasia.

Is there a test for FeLV infection?

Special blood tests have been developed. Most tests are designed to detect the presence of viral antigen in the cat’s blood. In general these tests are very reliable although rarely a false positive result occurs. In some situations it may be necessary to confirm infection with the virus through repeated blood testing.

Does my cat need to have a blood test before vaccination?

For the vast majority of cats, this is highly recommended. Remember not all FeLV-infected cats that test positive become sick. Approximately 30% of cats exposed to FeLV will eliminate the virus and will not contract the disease. Some FeLV-infected cats may not show signs of disease for months or even years.

How safe is the vaccine?

FeLV vaccines have been specially developed so that they do not contain any infective virus material. They are considered to be safe. You are unlikely to see any ill effect of the vaccine apart from some mild sluggish behavior a day or two after the vaccine is given. A very few cats may have a mild allergic reaction. Most vaccine reactions occur almost immediately and your veterinarian will provide appropriate treatment. If you are concerned that your cat is experiencing an abnormal reaction in the hours or days following any vaccination, please call us.

How effective is FeLV vaccination?

FeLV vaccines have now been available for many years and they have been continuously improved. They are helpful in preventing infection with FeLV and thus controlling FeLV-related disease. Unfortunately, no vaccine is 100% protective. Where possible do not allow your cat, particularly a kitten, to come into close contact with known FeLV-infected cats or cats of unknown vaccination history.

How often is revaccination necessary?

Revaccination is necessary in the initial course of vaccines to provide strong lasting immunity. Even so, immunity does decline over time and your veterinarian will advise you of the recommended revaccination schedule for your pet based on your cat’s lifestyle and needs.


  This client information sheet is based on material written by Ernest Ward, DVM

© Copyright 2005 Lifelearn Inc. Used with permission under license. October 13, 2015

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