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Feline Leukemia

Feline leukemia is a viral infection of cats that can lead to immunosuppression and malignant neoplasia(cancer). Cats coming from multicat households and catteries as well as cats coming into contact with outdoor cats are more at risk. Infected cats shed virus in their saliva and urine. Transmission occurs more commonly during grooming and playing.

Virus can also be transmitted through blood (e.g.,transfusion) and by the queen through the placenta. The virus is sensitive to desiccation, heat and desinfectants so survival in the environment is not a big concern.

So the virus enters through the mouth then multiplies in the throat. If the cat’s immune response is adequate, infection won’t occur. On the other hand, if immune response is inadequate, viremia (virus in the bloodstream) will set in and the virus will spread to the lymph nodes. Once again, at this stage, the virus could be eliminated through adequate immune response. In that event, the virus will then reach the bone marrow where it will replicate, infect white blood cells and platelets and return to the bloodstream. When the virus will have infected the salivary glands and bladder, the cat will excrete the virus in saliva and urine.

Infected cats can show nonspecific signs such as fever, loss of appetite and lethargy. Those signs are usually associated to recent viremia. Weakness and anorexia could also be caused by anemia or malignancy. Weight loss, infections that reoccur, diarrhea, chronic nasal and ocular discharge could be signs of chronic Felv infection.

Upon physical exam, we could note depression, weakness and overall bad health. Immunosuppression can be the cause of chronic infections and cancer. Anemia, enlarged lymph nodes and haemorrhages can be seen. Sometimes a thoracic mass can cause breathing difficulties.

Different tests are available for diagnosis of Feline Leukemia. The ELISA (enzyme-linked immunosorbent assay) and an IFA (immune fluorescent assay). The first test detects free virus within the bloodstream and the second one detects the virus within white blood cells and platelets. A positive result on the latter means that the bone marrow is actively producing virus.

The ELISA test is an affordable screening test that can be done in clinic. If the test is negative, we assume it is true because the test will detect very small amounts of the virus in the bloodstream. If the ELISA test is positive, we will want to confirm it with an IFA test. This test is done in a private lab and if the result is positive will confirm that the cat really has feline leukemia permanently.

So if both tests are positive, this means that the cat is viremic and will remain infected for the rest of its life. Some cats can be negative both on the ELISA and IFA and be latent carriers, if Felv infection is suspected testing on bone marrow is required.

Within 4 years, 90% of the infected cats will have past away from the disease but often their quality of life remains very good. Cats that have leukemias (increased white blood cell count) and other bone marrow anomalies or those that develop lymphoma have a poorer prognosis.

The best to prevent feline leukemia is to prevent cats from going outside. If this is not possible, vaccination is very effective. Vaccinating cats that are already infected will not cure them even though it wouldn’t be harmful. However extremely rare, vaccination for feline leukemia has been associated with sarcomas at the site of injection. The benefits of vaccinating greatly outweigh the risks of sarcoma formation. Young kittens are most vulnerable and must be tested vaccinated before being introduced to other cats.
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