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(Opinions compiled by Rita Bybee from research on the internet, just for information only and not professional opinion)

What is feline leukemia?  It is a cancerous disease caused by the leukemia virus (FeLV). It causes diseases other than the leukemia including other than leukemia. They may not show signs for months or years. Approximately 2.3% of cats in the Unites States are infected with FeLV. 

What are the characteristics of this dreaded disease? It is a type of virus called a retrovirus, in the same family as the FIV virus and human HIV virus that causes AIDS. This FELV virus will only infect cats and cannot be spread to humans.

What are the symptoms of FELV? Many times a cat who has the FeLV virus will not manifest any symptoms for many months possibly to years. Some of the signs include (this is in the acute phase) fever, lethargy, diarrhea, and swollen lymph nodes). However, some things to keep in mind when a cat is exposed to FeLV:

  1. Some cats will not be infected due to inadequate exposure or a good immune response.

  2. Some cats develop a latent infection, meaning they will not be able to destroy all of the viral

RNA and DNA but they can hold the disease in check, meaning it is a latent or regressive disease. These cats show no signs and do not shed the virus in their saliva or other bodily secretions (there is some controversy over this, though, in that it is still in their DNA and later on they can reactivate the disease due to different factors, and that they could also still be carriers. I’ve read different opinions regarding this.)

  1. Some cats will become persistently infected in that they don’t develop an adequate immune response and will remain permanently infected.  This is considered progressive. They shed large amounts of virus in their saliva and often develop FeLV-associated diseases with a few years.

  2. Little kittens are especially susceptible when exposed to FeLV , since almost all of them exposed to FeLV less than 8 weeks of age will show signs of the disease and become permanently infected.

What ailments/diseases are associated with FeLV infection?

  1. Weight loss

  2. Fever

  3. Immunodeficiency and infections

  4. Anemia

  5. Immune-mediated diseases

  6. Reproductive problems such as sterility, etc.

  7. Gastrointestinal disease such as stomatitis.

  8. Neurologic disease

  9. Platelet disorders

  10. Lymphadenopathy

  11. Cancer

  12. Respiratory and eye problems

  13. Oral disease

How is FeLV diagnosed?

The ELISA test (also known as the Snap test), is one of the most commonly used tests for FeLV in cats at the vet office. It can usually be done with results in about 10 minutes, and with all of the research I have come across, is very effective. It is done by taking a blood sample from the cat.  If the sample comes back positive, then a confirmatory test, called IFA, should be performed. If the IFA comes back negative, then there are usually 2 possibilities. One is a false positive ELISA test and the other is a stage of the disease is present at which the IFA test does not detect infection. Therefore, the cat or kitten should be isolated and re-tested in at least 6 weeks. If at that time the IFA is positive, you know the cat is infected. The IFA is 99% accurate. An IFA positive cat can be shedding the virus and infect other cats and kittens!

Should I breed cats that have tested positive on ELISA and negative on the IFA confirmatory test? Read this interesting article from Dr. Nell Barrett Salter at: A very significant part of this article is as stated below in quotes in reference to this question:

“Sixty to eighty percent of cats with a healthy immune system who are exposed to the FeLV virus develop antibodies that prevent progression of the infection. However, a percentage of infected cats will progress to a bone marrow infection and go no further, thereby harboring the virus in the bone marrow. These cats can test negative on both tests, or positive on the ELISA and negative on the IFA. For breeders, this dilemma is significant. If a cat is harboring virus in the bone marrow, it can appear healthy and normal. But a stress, such as pregnancy, can cause a reappearance of the virus, and infection and transmission of the virus. If you think about this, you will understand that even testing new cats and kittens entering your cattery will not completely safeguard you against FeLV. This is the reason that I recommend routine FeLV testing of all breeders at least every 6 months, and testing of all kittens before going to their new home or before being kept as replacement kitties. I personally recommend that a cat who has ever been positive (ELISA or IFA) should NOT be used in the cattery as a replacement. You may lose some prospective breeders this way, but "better safe than sorry."”

Introducing a New Cat to a Home Where a Cat has Tested Positive for FeLV on ELISA and then Negative on IFA.  I would recommend never letting a new cat or kitten have any contact with a cat who has ever tested positive for this disease, and I would also recommend never breeding them, just to be safe. I would keep them separate, and ultimate I would try to find new homes for cats who don’t have other cats but who have  tested positive. It is best not to home cats who are infected with those who are noninfected.

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