Feline Leukemia Virus

Feline Leukemia Virus is in the retroviral family of oncornaviruses. This class of RNA viruses function by converting their RNA into DNA using an enzyme called reverse transcriptase. They then integrate their DNA into the host’s DNA. After infection the virus either integrates its DNA into the host and remains latent in the host cell, or the virus integrates itself and then begins to replicate itself on a grand scale. Also when the host cell replicates itself (as cells often do) it creates copies of virus RNA with its own DNA. The FeLV virus specifically infects cells of the bone marrow, red blood cells, and lymphocytes (white blood cells).

The feline leukemia virus is excreted in bodily fluids (saliva, tears, possibly urine and feces). The leukemia virus does not survive well outside of the body, so your cat will need bodily fluid contact (sharing food bowls, litterboxes etc.) with an infected cat to become FeLV+ him/herself. Many cats, although being exposed to the virus, become immune to it and will not even carry the virus in their blood or bone marrow. Other cats carry the virus (these cats will test as FeLV+) but do not appear to be ‘sick’. These cats can live a long and healthy life as a carrier of the disease. However, they are carriers and can infect other cats in your home. Usually these cats, unless stressed or immunocompromised, never show signs of disease. A cat, once ‘ill’ with the disease can survive for weeks, months or longer with the proper treatment. About 30% of all cats who come in contact with the virus will actually show signs of disease. Cats can get three primary diseases from infection with FeLV: 1) leukemias or cancer of the white blood cells 2) lymphosarcomas or cancer of the lymphoid tissue and 3) immunosuppressive related diseases (anemias, respiratory infections etc.). There is no cure for FeLV but you can help your cat live a good healthy life for an extended period of time with effort, love and the proper care.

As of now it is not thought that FeLV can be spread to humans and there does not seem to be a link between AIDS patients and FeLV. However this has not been definitively proven so if you have AIDS you may want to be very careful when handling an FeLV+ cat.

Symptoms to look for:


  • Lethargy
  • Depression
  • Weight loss
  • Decreased appetite
  • Diarrhea
  • Blood in the stool
  • Incontinence
  • Vomiting
  • Enlarged lymph nodes
  • Respiratory distress
  • Increased drinking
  • Increased urination
  • Secondary infection
  • Chronic diseases
  • Cancer
  • Liver/Kidney disease
  • Jaundice (yellowing of the skin)
  • neurological problems


Your vet will draw blood from your cat and perform an ELISA (enzyme linked immunosorbent assay) test. An IFA (immunofluorescence assay) can also be done, however this test will need to be sent out to a diagnostic lab and takes longer to get results from. Both tests detect the virus but in different compartments of the body (serum vs. wbc’s). This shows the presence of the virus at different stages in it’s life cycle (ELISA can detect infection at any stage whereas IFA only detects virus in later stages of infection). If your cat is tested and tests negative it could have the virus in a very early stage that isn’t showing up yet, or the virus could be in such a cycle that it isn’t seen in the blood at the time of the test. Thus if your cat has all the symptoms and these symptoms are unexplained by other diseases, and your cat tests negative for FeLV you may want to have him/her retested at a later date.

There currently is no cure for FeLV. If you have an FeLV positive cat you need to be very diligent about treating all of the secondary infections and symptoms. This can help keep the cat healthy, strong, and extend his/her life. Some therapies used to directly combat the virus are chemotherapeutic agents and antiviral drugs (including interferon). These have been found, in some cases, to produce temporary remission. Some cats may also benefit from steroid therapy (prednisone) as this can decrease the number of circulating white blood cells and abnormal or cancerous blood cells, and inhibit the cell-mediated immune response. Other drugs that are being used for treatment of FeLV (some are controversial) include AZT (antiviral drug used to decrease viral load), immunoregulin (stimulates the immune system’s cell-mediated response), acemannan (an aloe vera derivative which has been shown to stimulate the immune system, help the body produce interferon, and possibly combat certain viruses) and Staphylococcal A (an immune stimulant which may or may not be helpful). However the best approach at this time seems to be treating all of the secondary infections, while giving a combination of interferon and prednisone.

Precautionary measures:

There is a vaccine for FeLV that has been found to be reasonably successful. This seems to be the best line of defense today. Before bringing any new cat into your home make sure that he/she has been tested and vaccinated. You can also get yearly boosters at your vet’s office. Other than that, keep your cat indoors if you can, to limit the possibility of your cat coming in contact with an FeLV+ cat.

As FeLV is contagious you will need to protect other cats in your home if you have an FeLV+ cat. The best thing to do is to make sure that they are all vaccinated and keep the FeLV+ cat separated from the other cats. As you will have contact with both sets of cats you will need to be careful about spreading the disease. Make sure to wash your hands between handlings and if you clean the litterbox or have any cat saliva on your clothes, you should also change clothes in between handling cats. Your home should also be routinely disinfected with a bleach containing solution to kill any viruses that may be free in your home. This will make sure that even though your cats are separated that no virus spread through the home.

Please click here to read about Mariah. Mariah had FeLV and was put to sleep on May 9, 2000. This link includes a tribute to Mariah and links to other FeLV information.