Feline Leukemia Virus (FeLV)

FeLV is a very serious disease of the feline world. It is caused by a retrovirus (FIV is also caused by a retrovirus) that is spread from cat to cat by saliva, urine, and respiratory secretions. This means that cats that share litter pans and feeding bowls, along with cats that fight, are at risk. Kittens born to mothers that have the virus may also be infected.

Most cats that get exposed to the virus develop antibodies and are able to fight it off. This is especially true for cats that are free of parasites, are current on their routine vaccines, and are fed a good diet. Cats that have minimal exposure to other cats are at significantly less risk of getting this disease.

The ability to identify FeLV positive cats has been a significant factor in the reduction of FeLV exposure and infection.

Several outcomes are possible if your cat is exposed to this virus:

• It makes antibodies and fights off the virus
• It becomes a carrier of the virus without showing any symptoms initially. These cats can spread the virus to other cats easily because they show no signs of illness. After a variable period of time these cats will probably develop one of the diseases associated with the virus.
• The virus weakens the immune system and various problems of a chronic nature (anemia, infections, etc.) develop.
• It causes a serious cancer of the lymph nodes. This is why it was called Feline "Leukemia" Virus when first discovered.

Symptoms

There are no specific set of symptoms that tell us for certainty that a cat has FeLV. Cats that have this virus will commonly have fevers (>103 degrees F), poor appetites, are lethargic, suffer from recurring infections, and will have experienced weight loss. These symptoms are quite variable though, and are also present with other diseases, so a correct diagnosis is important. Cats that are carriers of the disease may not have any symptoms.

Cats that have FeLV are susceptible to other diseases, notably FIA (Feline Infectious Anemia). FIA is caused by a blood parasite called Hemobartonella. This parasite will either cause anemia by itself, or worsen the anemia caused be FeLV.

Testing Recommendations

Testing for FeLV is our first line of defense. Our hospital follows the recommendations of the American Association of Feline Practitioners/Academy of Feline Medicine. Their recommendations are summarized as follows:

• The FeLV status of all cats should be known
• Testing and identifying positive cats is the mainstay of managing this disease
• All new kittens and adult cats should be tested before introduction into any house
• Kittens can be tested at any age
• Vaccination with FeLV vaccine does not interfere with the FeLV test
• The ELISA (Enzyme linked immunosorbant assay) test is the preferred screening test
• All positive screening tests should be repeated
• The IFA (Immunofluorescent antibody) test should be used to confirm a positive ELISA test
• All cats with negative test results that are exposed to FeLV positive cats should be retested not sooner than 90 days after exposure
• Testing of outdoor cats or those at risk for exposure to the virus should be performed annually
• Any cat in a multiple-cat household found to be FeLV positive should be isolated from other cats
• FeLV positive cats can live a high quality life for months to years

Testing Procedure

Our in house FeLV test is the ELISA test. It checks for evidence of the virus in blood saliva, or tears. Cats that are positive on this test should be rechecked in 30 days since some of them can become negative. This test also checks for antibodies to FIV (Feline Immunodeficiency Virus) at the same time. This added convenience minimizes cost and requires less blood than if 2 separate tests were run. In addition, it is highly accurate, and can be performed within 15-20 minutes.

Specialized equipment and training is needed to accurately run the ELISA test. The bottle with the dark blue top is the reagent used to start the chemical reaction needed to read the test. A few drops of blood are all that is needed. The test kit the blood will be placed into is called a Snap test, because the right hand side of it is snapped down to complete the test.

After being placed in the reagent solution, the blood is transferred to the diagnostic test kit well. The blood immediately starts flowing towards the white circle in the center of the test kit. It takes 30-60 seconds to reach the white circle

When the blood flow reaches the center circle the kit is activated by pushing down on the elevated area on the right side of the test kit. After a few seconds the blood starts flowing back to the left.

The blood eventually flows all the way back to its starting point. After 10 minutes a blue dot appears, signifying that this cat is negative for both FeLV and FIV.

The three different type of positive results that are possible:

There is an additional test for the FeLV called the IFA (Immunofluorescent Antibody) test that checks for evidence of the virus in white blood cells. This test is used to confirm a positive ELISA test, and signifies a persistent infection. It is not used as an initial screening test like the ELISA test because it can miss the initial stage of virus infection in the blood stream. This test needs to be sent to our outside laboratory, and is used only when one of our doctors feels it is necessary.

Treatment

There is no medication that will kill this virus. Treatment is aimed at keeping the immune system as strong as possible and utilizing medication as needed. Several disease syndromes are associated with this disease, especially since the virus is immunosuppressive:

• Anemia can occur because the virus attacks the bone marrow and prevents the production of red blood cells. Anemia is diagnosed by a blood sample that counts the red blood cells. It is treated with vitamins, anabolic steroids, immunostimulants, erythropoetin, and even blood transfusions. Pets that are anemic tend to be lethargic and have poor appetites. Cats that are anemic due to the FeLV need their red blood cells checked every 3 months on a routine basis. Fortunately this test is inexpensive and can be performed in our hospital in a few minutes.
• Chronic wounds or infections are another common problem associated with FeLV. They are treated with proper wound care and antibiotics. Symptoms of this problem could be lethargy, poor appetite, swelling, draining wounds or soreness when petted.
• Malignant cancer of the white blood cells or lymph nodes occurs on occasion. This is a serious complication of the disease and requires specialized medical and surgical care. Pets with this syndrome of the FeLV virus might show signs of weigh loss, have poor hair coats and poor appetites.
• Associated disease like FIA can occur due to immunosupression. This is a parasite of the red blood cells that can worsen the anemia that might already exist. It is treated with the use of special antibiotics, but may be difficult to control due to the effect the FeLV has on the immune system.
• Diseases of internal organs like the liver, kidneys, brain, lung, GI tract, and eyes are also associated with FeLV. Diseases of these organs are also treated with symptomatic care.

FeLV Vaccine

The vaccine for FeLV is highly effective, and all cats that go outside or are at risk should be vaccinated for this virus after testing negative on a blood sample. It will not reverse the deleterious effects of a cat that already has one of the diseases associated with FeLV. Initially it is given to kittens after 9 weeks of age, and reboostered 2-4 weeks later. If the second vaccine in the 2 vaccine series is given greater than 4 weeks after the first, an additional vaccine needs to be administered 2-3 weeks later. After the initial series, yearly boosters are given. If your cat goes outside frequently, we recommend yearly FeLV testing along with vaccination.