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Preventative Pet Health Care Series: Feline Leukemia – Core or Non-Core Vaccine?



Feline leukemia is caused by a retrovirus for which there is no cure once a cat is infected.  Many cats may contract the virus and be latent carriers that do not show outward signs of disease for months to years, potentially spreading the disease to other cats during this time, while themselves not showing any signs of disease.   Most feline leukemia positive cats die within 3 years of infection.

Feline leukemia virus can be transmitted in three ways.

1.)    Saliva of an infected cat coming in contact with eye, mouth, nose, and genital membranes of non-infected cats via licking or biting.

2.)    Passing of blood into non-infected cats as commonly occurs during coitus or fights.

3.)    Mother to fetus during pregnancy.

Feline leukemia primarily infects the bone marrow of cats, leading to deficiencies in blood cells that the bone marrow is responsible for synthesizing.  This commonly leads to anemia and low white blood cells.  The latter is the feline immune system’s first line of defense, thus feline leukemia commonly leads to opportunistic infections and cancers (much like HIV does in people).   Direct degenerative disease can occur in any tissue or organ system that the virus subsequently invades.

There is no cure for feline leukemia, with treatment generally aimed at management of disease.  Once in full blown disease, management commonly becomes expensive and of limited benefit.  Management may include chemotherapy, interferon, Protein A, steroids, and supportive measures.


All new cats with an unknown medical history or who have never been retroviral tested before should for feline leukemia prior to introduction to an environment with non-infected cats.   Any household with at least one cat that has access to outside should be immunized yearly with the feline leukemia vaccine.  This would make feline leukemia a core vaccine for cats that have access to outdoors (and therefore access to other cats that kmay be feline leukemia positive).

 Some veterinarians do not consider feline leukemia a core vaccine for indoor cats, since they feel that strictly indoor cats with no access to other cats are not candidates for the vaccine, carrying very little risk.  Other veterinarians consider feline leukemia a core vaccine for all cats given lack of compliance of many feline owners to engage in proper testing prior to adding new cats to a household; and many cats having a tendency to try to escape outdoors.

I can understand both stances.  My position is a bit of a hybrid of the two.  With kittens being the most susceptible to disease, as well as taking into consideration feline escape tendencies and feline leukemia screening compliance issues; even for kittens slated to be indoor cats with relatively low risk of disease, it is advisable to administer the feline leukemia vaccine at 9 weeks, 12 weeks, then boostered one time one year later.  From my view, this middle ground imparts some immunity to account for possible accidental/incidental exposure to feline leukemia virus, while avoiding over-vaccination for generally low risk feline patients.

Dr. Roger Welton is the President of Maybeck Animal Hospital in West Melbourne, FL, Chief Editor of the Veterinary Advice and Information Website, Web-DVM, and founder/CEO of Dr. Roger’s Holistic Veterinary Care.

One thought on “Preventative Pet Health Care Series: Feline Leukemia – Core or Non-Core Vaccine?

  1. says:

    can dogs take human penicillian its 500 milligrams ,she is 12 years old and has a mass that has gotten bigger in the last week by her nipple she has had only one litter of pups years ago it started out small like a bite or like a clog but today it is much bigger she isnt crying or anything but has become very distant,she lets me feel it and don’t jump or anything like that when I do but I am so worried and I live on a limited income what can I do please help me help her she is my grand dog and I love her so much but I am at a loss

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