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Care Guide

About Care Guides[x] These care guides are written to help your clients understand common conditions, tests, and procedures, as well as to provide basic information about pet care. They are based on the most up-to-date, documented information, recommendations, and guidelines available in the United States at the time of writing. Pharmaceutical product licensing, availability, and usage recommendations are based on US product information. Use the Download Handout button to generate a PDF for printing or e-mailing to your clients.

Feline Leukemia Virus

    • Feline leukemia is a contagious disease that can be fatal among cats.
    • Feline leukemia has been linked to the development of certain cancers in cats.
    • Cats that go outside are at increased risk for exposure to feline leukemia.
    • Vaccination can aid in the prevention of disease associated with feline leukemia.

    What Is Feline Leukemia?

    Feline leukemia virus (FeLV) is contagious among cats.  Unlike many other viruses that enter specific cells in the body and destroy them, FeLV enters certain cells in a cat’s body and changes the cells’ genetic characteristics. This permits FeLV to continue reproducing within the cat each time infected cells divide. This allows FeLV to become dormant (inactive) in some cats, making disease transmission and prognosis (outlook) difficult to predict.

    How Do Cats Become Infected With Feline Leukemia?

    Feline leukemia is generally transmitted through contact with saliva from an infected cat. Other body fluids, like nasal secretions, urine, feces, and milk, can also contain virus. Certain “social” behaviors such as mutual grooming and sharing food or water bowls can spread the disease; some cats become infected through bite wounds. Kittens can become infected during fetal development or during the first days of life as their mothers nurse and care for them.

    FeLV is killed by many disinfectants and does not live for very long in the environment, so contact with an infected cat (or food/water bowls) is the most common way for the disease to spread. However, predicting which cats can transmit the disease is complicated because some cats that are potentially contagious may not show signs of illness. 

    Signs of Feline Leukemia

    Not every cat that becomes infected with FeLV develops clinical signs or long-term complications associated with the virus. However, some cats may experience various illnesses and immune suppression before eventually dying of FeLV-associated complications.

    Because FeLV can affect almost any organ system in the body, associated clinical signs and illnesses can vary significantly and include the following:

    • Anemia (inadequate numbers of red blood cells)
    • Leukemia
    • Immune suppression
    • Fever
    • Lethargy (tiredness)
    • Chronic respiratory infections
    • Chronic oral and gum infections
    • Cancer of the lymphatic system (and other cancers)

     Diagnosis and Treatment

    Because there are several stages of disease and not every cat handles FeLV infection the same way, diagnosis is not always straightforward. Some infected cats test positive on routine FeLV screening tests, whereas specific tests on blood or bone marrow are required to confirm infection in other cats. Some cats may test positive on blood tests when they are young kittens but test negative later. Similarly, some cats may test negative at one point and test positive later as the virus progresses through various stages in the body. Because FeLV infection can have many clinical presentations, your veterinarian may want to test your cat if he or she seems to be ill—especially if a fever is present. Some cats need to have multiple tests done to confirm infection.    

    Treatment options for FeLV are limited, and no treatment can eliminate the virus. Some antiviral or immunomodulating drugs have been investigated, but most treatments are aimed at managing the clinical signs and complications. Cats that are anemic may receive blood transfusions; cats that are dehydrated or not eating may receive intravenous fluids and feedings; chemotherapy is sometimes helpful in managing cancers; and antibiotics may be used to treat associated infections.

    Vaccination and Prevention

    Several vaccines are available for preventing disease associated with FeLV. All of the available FeLV vaccines have been tested and found to be safe and effective when administered as directed.

    Kittens are generally vaccinated against FeLV around 8 to 9 weeks of age. A booster vaccination is given 3 to 4 weeks later according to the vaccine label, followed by boosters each year as long as the risk for exposure remains. Cats that go outside or live with other cats are at greater risk for exposure to FeLV compared with cats that stay indoors and have limited contact with other cats. If risk for exposure is low, your veterinarian may not recommend the FeLV vaccine for your cat. Ask your veterinarian about how to protect your cat from this disease.

    Because FeLV is transmitted through contact, keeping sick cats separated from healthy cats can reduce the likelihood of transmission. Any new kitten or cat being introduced into the home should be examined by a veterinarian as soon as possible and separated from all other household pets for a quarantine period of several weeks. During that time, the new cat should be tested for FeLV and monitored closely for any signs of illness. Any problems should be reported to your veterinarian before introducing the new cat to your other pets.