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Feline leukemia

What Is Feline Leukemia?

Feline leukemia is a deadly viral infection in cats caused by the spread of the feline leukemia retrovirus. Feline leukemia results in the mortality of numerous cats every year. The disease produces reverse transcriptase, an enzyme that inserts virus copies into the genetic material of cells, functioning similarly to Feline Immunodeficiency Virus.

The disease is not extremely common infecting approximately 2-3% of cats in the United States. It can be spread more easily in cats that are already ill and in kittens that are very young. In cats that are diseased or young the rate of infection rises to more than 13%. Feline Leukemia is most commonly acquired through contact with other cats.

Transfer of saliva from an infected cat to a healthy cat is the most common route of viral infection, although lower levels of virus particles are also found in urine, semen and feces. Transmission occurs by licking, biting and sneezing. Food, water dishes, and litter boxes are likely sources of infection when they are shared with an infected cat. It can also be transferred to kittens from an infected mother, though this is rare.

What Does It Do?

The virus has several negative effects that can be particularly harmful to cats. The disease itself is a cancer that primarily infects bone tissue which can lead to a variety of blood disorders. As bones are the site of lymphocyte production, infection in bones can prevent white blood cells from being produced properly.

A lack of proper white blood cells can impair the immune system of cats in a manner similar to that of the AIDS virus in people. Feline leukemia is therefore very comparable to Feline Immunodeficiency Virus, as it can cause cats to lose their ability to fight disease-causing bacteria, viruses and fungi. The normal bacteria and viruses that a healthy cat can ward are therefore the cause of many of the diseases associated with feline leukemia.


Cats with feline leukemia can exhibit:

  • Anemia
  • Atrophy of the thymus gland
  • Ulcers of the mouth
  • Skin lesions
  • Reproductive problems such as miscarriages and weak or dying kittens (fading kitten syndrome
  • Chronic digestive and respiratory problems
  • Persistent Fever Gingivitis and Stomatitis
  • Persistent diarrhea
  • Seizures
  • Enlarged lymph nodes

  • Treatment

    If your cat becomes infected with leukemia, there are 3 possible outcomes: Approximately 40% develop immunity and become resistant to future infections. About 30% become latent carriers, where they are neither fully recovered nor seriously affected. These carriers can be susceptible to the disease at some future point, and if reactivated, they can pass the virus to their offspring. The remaining 30% are persistently infected and, of these, 83% die within 3 years of the time of infection from leukemia or its associated diseases. Cats can die suddenly or after suffering for prolonged periods.


    Cats can be tested for leukemia using a simple blood test (done by your veterinarian). The most important step in prevention is vaccination. Kittens can be vaccinated starting at 8 to 10 weeks. After the initial vaccinations, boosters are done once yearly. You can also try Fel-O-Vax Lv-K as it protects against feline Leukemia Virus, and for healthy cats 8 - 10 weeks of age or older.

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