Feline Leukemia Virus

If you are debating whether to keep your cat indoors and/or let him roam outside, one of the best reasons to keep your cat(s) indoor is the presence of the Feline Leukemia Virus. Outdoor cats are considered to be high risk with as many as 13-16% of the population estimated to be positive for the virus. 

How Feline Leukemia Virus is Transmitted

There are a number of ways a cat can be exposed to the virus. It is spread primarily through saliva, although other bodily fluids such as urine, feces, and nasal secretions are possible modes of transmission as well. Therefore, sharing of food and water bowls and litter boxes, grooming each other, mating, bite wounds and blood transfusions are the main ways cats are exposed to the leukemia virus. Kittens can also be infected while in the mother's uterus or from nursing from the mother cat. Because of this, the cats that are most at risk are cats that go outside, young kittens, and any cat that shares a home with an FeLV positive cat. 

Signs of Leukemia Virus

  • Loss of appetite
  • Poor hair coat
  • Fever that is non-responsive to treatment
  • pale mucous membranes, which are the result of serious anemia
  • Lymph nodes that are swollen
  • Decrease in weight - in later stages, there is serious loss of muscle and body weight
  • Behavioral changes and neurological problems such as seizures
  • Eye problems of all types
  • Reproductive problems in females
  • Liver disease and/or intestinal disease
  • Cancer (lymphosarcoma and leukemia)
  • Suppression of the immune system making the cat susceptible to a variety of infectious diseases  (respiratory, mouth, fip, poor wound healing, abscesses and chronic generalized infections)
  • Skin infections, urinary tract infections, and upper respiratory tract infections
  • Diarrhea that doesn't go away
  • Gingivitis (inflammation of the gingiva (gums) which can be present throughout the mouth and even into the throat.

Stages of Feline Leukemia Virus Infection

If a cat encounters the Feline Leukemia Virus, there are two possible stages of infection that can take place.


Primary viremia is the term applied to the stage during which some cats will be able to rid their bodies of the virus with a strong immune response.


Secondary viremia refers to a subsequent stage that affects the cats that were not able to fight off the virus during the primary stage. In this stage, the bone marrow and other tissues have been invaded by the virus. The virus can then remain in a passive state in the bone marrow for quite some time. These cats will, for the remainder of their lives, have the virus in their bloodstream, able to reproduce. 


Feline Leukemia Virus is diagnosed with blood tests. There are 2 types of blood tests: the Eliza test (enzyme-linked immunosorbent assay) and the IFA (immunoflourescent assay) test. Eliza is the test that is initially performed, often in your veterinarian's office, while the IFA is a confirmatory test that is sent to an outside commercial laboratory. Both tests operate on the basis of detection of a certain protein in the cat's blood. 

Which Cats Should Be Tested

All cats should be tested for Feline Leukemia according to guidelines suggested by The American Association of Feline Practitioners. This is due, in part, to the fact that this virus causes more illness and death than any other disease that affects cats. 

Treatment and Prevention


Even though your vet may have some suggestions for treatment, none are curative, so the best way to treat FeLV is not to get it in the first place. Prevention is the most effective thing you can do:


(1) keep your cats indoors


(2) test all potential adoptees. Only adopt negative cats.


(3) If you have cats that are positive for feline leukemia as well as negative ones, keep them completely separated from each other.


(4) Talk to your veterinarian about the leukemia vaccine if your cat falls into any of the risk categories. It may be wise to vaccinate all kittens during the first year of life since they have greater susceptibility and they may slip out doors or the owner may change his mind and decide to let the cat spend time outdoors.

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