I. What is Feline Leukemia Virus?

Feline leukemia virus, or FeLV, is what is known as a Retrovirus. The Retroviruses are the family of viruses to which HIV, or human immunodeficiency virus, belongs. All domestic cats and some exotic cats can be infected with FeLV. The virus is found worldwide.

FeLV is shed in the blood, saliva, tears, nasal discharge, urine and feces of infected cats. Cats are exposed and become infected with FeLV when they come into contact with an infected cat that is shedding virus particles. Contact can be as simple as using the same food and water dishes, using the same litter box, or mutual grooming, or it can include fighting, hissing, and bite wounds. The most common means of exposure is usually casual contact such as mutual grooming. Kittens can get the infection from their mother before they are born or as she cleans, grooms, and nurses them when they are very young. Cats that go outdoors and cats that are frequently around unfamiliar cats are more likely to be exposed and become infected with FeLV. Young kittens are much more susceptible to infection than older cats are, but cats of any age can become infected if they are exposed to enough virus particles.

After a cat is exposed to the virus, usually via the nose and mouth, the virus replicates in the tonsils and infects white blood cells there called lymphocytes. In the lymphocytes, the virus is carried, via the bloodstream, to the spleen, lymph nodes, bone marrow and intestines. If the cat’s immune system is able, it will destroy the virus in the cat’s body at this stage and before it is able to infect the bone marrow. Once in the bone marrow, the virus infects neutrophils (other white blood cells) and platelets which are released from the bone marrow into the blood. Neutrophils and platelets in the blood carry the virus through the entire body where it can infect many other tissues including the salivary glands and tear glands. From these glands, the virus is shed in the tears and saliva of an infected cat and can be passed to other cats. A cat can shed virus particles and pass virus on to other cats even if it does not have symptoms of disease.

Once a cat is exposed, there are several possible things that can happen

• Persistent infection with shedding of the virus can occur in healthy appearing as well as sick cats.


• Elimination of the virus by the immune system with no persistent infection.


• Short term circulation of the virus in the blood followed by a hidden (latent) infection in the bone marrow, spleen, lymph nodes, or intestines. This only happens in a small number of cats


• Reactivation of a hidden infection with circulation of virus in the blood and shedding of the virus.

II.What to Watch for at Home – Symptoms

Because FeLV suppresses the immune system and is carried in the blood to all parts of the body, it can cause diseases in all parts of the body. The virus can cause or lead to cancer, most commonly lymphosarcoma or leukemia. It also suppresses the immune system leading to many other infections by viruses, bacteria, or fungi which might not be a problem for cats with a normal immune system.

While any age or breed of cat can get FeLV, it is most commonly seen in young male cats because they are the most likely to roam, fight, and come into contact with unknown cats.

The symptoms that can be seen are:

• Loss of appetite


• Weight loss


• Depression


• Enlarged lymph nodes


• Chronic infection in the skin, respiratory tract, or urinary tract


• Diarrhea


• Vomiting


• Bad breath and sores in the mouth


• Difficulty breathing


• Enlarged abdomen


• Stillbirth or infertility in un-spayed female cats


• Difficulty walking or weakness


• Leaking urine while sleeping (urinary incontinence)

Not all cats infected with FeLV will have symptoms. Some cats can be infected with the virus and shedding the virus without any symptoms.

III.The Veterinary Visit – How to Tell if a Cat Has an FeLV Infection

FeLV infections are diagnosed with blood tests. There are two types of tests available both of which look for the presence of the virus in the blood. The ELISA test is the type of test that is done in the veterinarian’s office. It can detect the virus in the early stages of infection before the bone marrow becomes infected. A small sample of blood is drawn for the test and the results are obtained in ten to fifteen minutes.

The other available test is the IFA. An IFA test needs to be sent out to a laboratory. The IFA test looks for virus in neutrophils and platelets. This stage of infection occurs after the bone marrow is already infected.

Because an ELISA test can detect FeLV before the bone marrow is infected, it can be positive in a cat whose immune system may be able to destroy the virus before the bone marrow is infected. For this reason, any cat which tests positive with an ELISA test should also have an IFA test to confirm the results. An IFA test will not become positive until after the bone marrow has already been infected by the virus. Most cats that have a positive IFA test will remain infected with the virus for the rest of their lives.

For cats that have a positive ELISA test and a negative IFA test, both tests should be repeated at four to six week intervals for three months. If a cat is going to become persistently infected, both the ELISA and IFA should be positive at the end of the three month period. During this time, the cat should be isolated from other cats so that the infection is not spread.

Because cats with FeLV can have many other conditions as well, other tests might be necessary. These include:

• Complete Blood Count, Biochemical Profile and Urine Analysis. Common findings on these tests might include a low red blood cell count (anemia), leukemia, kidney failure, and liver disease.


• Blood tests for Feline Immunodeficiency Virus and Feline Infectious Peritonitis Virus. Because FeLV suppresses the immune system, infections with these other viruses may occur at the same time as infection with FeLV.


• Blood tests for other fungal or protozoal infections such as Toxoplasmosis.


• Fecal tests for intestinal parasites.


• Skin scrapings to look for mites such as Demodex cati or Notoedres cati.


• X-Rays and Ultrasound of the chest and abdomen to look for evidence of cancer or tumors


• Bone Marrow Aspirate or Biopsy. This test may help to determine the cause of anemia or help to diagnose some kinds of leukemia.

Many cats with FeLV develop some form of cancer or tumor. In these cats, a biopsy of the affected area or organ is necessary.

IV.Treatment

There are currently no known treatments that have been proven to be effective in fighting FeLV infection in cats that appear healthy. For cats that have symptoms associated with an FeLV infection, there are some treatments that have been tried. They include:

• Interferon-α, which may help to prevent the release of new virus particles from cells.


• Staphylococcus A, which helps to stimulate lymphocyte (white blood cell) activity and improves the function of the immune system


• Propionibacterium acnes, which helps to stimulate and improve the function of the immune system


• Acemannan, which stimulates immune function


• AZT, which helps to prevent the virus from replicating

Interferon-α, Staphylococcus A, Propionibacterium acnes and Acemannan work by stimulating the immune system and helping the cat to feel better. They may take four to six weeks to work. AZT may help to buy some time for other therapies to work in critically ill cats, however, it does not clear the virus in most cats. AZT can also cause severe side effects and should only be used cautiously in critically ill cats.

In addition to treatments directed at the FeLV virus, it is important to treat any other medical condition that the cat has. Antibiotics, antifungals or other medications will be needed to fight infections and may need to be given longer than normal because of the decreased ability of the immune system to fight infection. Chemotherapy or other cancer therapy may be needed if tumors are present.

At home, it is important to provide high quality food. A prescription diet from the veterinarian may be necessary. Vitamin supplements and antioxidants have not been shown to help but will not hurt and may provide some benefit. Regular check-ups and follow-up visits with the veterinarian can help diagnose and treat any infections or other problems that arise earlier so that they might be easier to manage.

FeLV positive cats should not be allowed to go outside to prevent the spread of the infection to other cats and also to help prevent them from being exposed to other diseases. Good flea control should be practiced to prevent the cat from getting any diseases that are carried by fleas. Flea control should be used even if the cat is indoors only. FeLV positive cats should not be allowed to eat raw meat or eggs as these can carry bacteria that might cause a serious problem. FeLV positive cats should not be allowed to hunt for this same reason. Unfortunately, cats with persistent FeLV infections usually develop cancer or severe secondary infections despite the best care and usually do not live more than two or three years after they are diagnosed.

V.Prevention

The best way to prevent infection with FeLV is to prevent exposure to the virus. Some important things that should be done to prevent exposure include:

• Keep all cats indoors and away from cats whose FeLV status is not known.


• Keep FeLV positive cats separated from FeLV negative cats. Do not allow them to share food and water bowls or litter boxes. FeLV is easily spread by casual contact so it is important to keep the cats completely separated.


• Before bringing a new cat or kitten into the household, have it tested twice for FeLV. Do the tests six to eight weeks apart. Keep the new cat isolated from the rest of the house until two negative test results are available.


• FeLV does not live long in the environment outside of the cat. Common disinfectants and hot water can be used to clean bowls and bedding that have been used by an FeLV infected cat.

There are vaccines available against FeLV. None of them are 100% effective in preventing infection, so it is still important to follow the preventative measures listed above. Vaccination is very important for cats that go outside or have contact with many other cats of unknown FeLV status. In rare cases, tumors can develop at the site of an FeLV vaccination, so it is important to assess each individual cat’s risk of exposure to the virus and vaccinate accordingly.

The following video is a discussion of retrovirus infections in cats.