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Feline Leukemia and Feline Immunodeficiency Virus


What You Need To Know About Feline Leukemia (FeLV) and Feline Immunodeficiency Virus (FIV)

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Feline Leukemia Virus (FeLV)

Feline leukemia is a serious disease in cats, caused by a virus infection. It is a complex disease, of which leukemia (cancer of blood cells) and cancerous tumors are only a small part. The other diseases that make up the leukemia virus complex include anemia, oral ulcers, skin lesions, chronic digestive and respiratory problems, and reproductive problems such as miscarriages and weak dying kittens.

The feline leukemia virus impairs the cat’s immune system similar to the way the HIV virus affects humans. As a result, cats lose their ability to fight the bacteria, viruses and fungi that cause disease.


Feline leukemia is spread by direct contact with infected cats. Kittens can contract the virus directly from an infected mother. The virus is usually transmitted in the saliva, but low levels of virus can also be found in urine and feces. Licking, biting and sneezing are common forms of transmission. Food and water dishes and litter boxes are likely sources of infections, if healthy cats share them with infected cats. Any cat that goes outdoors, even on a casual basis, is at risk of infection.

FeLV Testing

We strongly recommend testing every new cat, whether an adult or kitten, for leukemia virus. This is especially important if there are other cats in the household. Kittens can be tested as early as six weeks of age through a simple blood test run in our hospital. Ideally, kittens and new cats should be isolated from any other cats in the home until two negative leukemia test results are achieved. The second leukemiatest can be run 90 days or more after the first test. For young kittens (less than six months of age), we recommend the second test be run in combination with a Feline Immunodeficiency Virus (FIV) test at six months of age (see FIV information on the reverse). Two negative leukemia tests serve a strong assurance that this deadly virus will not affect your beautiful new feline family member. If your cat tests positive for the leukemia virus, your veterinarian will discuss the possible consequences to your cat’s health.


We recommend vaccinating all kittens for the leukemia virus in their first year with a two-booster vaccine series. This protects new kittens from the virus until a firm committed decision has been made about whether the kitten will remain exclusively indoors or whether she/he will be allowed outdoors. If at any time an indoor cat becomes an indoor/outdoor cat, the leukemia virus vaccine can then be boostered on an annual basis. If the cat remains exclusively indoors, further boosters are optional. We encourage you to discuss the decision with your veterinarian.

Feline Immunodeficiency Virus (FIV)

Feline Immunodeficiency Virus is also a serious disease in cats, caused by a virus infection. The general symptoms of the disease are immunodeficiency, cancer, and neurological disease. FIV mimics the HIV virus in its progression – however humans are not at risk of contracting either virus from cats. The immune system’s T-helper cells are affected first and the destruction of these cells over time leads to a less and less effective immune system. The lymph nodes enlarge and the cat loses the ability to fight off common bacterial, viral, and fungal diseases. Mouth and skin infections are common and may progress to more serious infections, until finally, the immune system fails completely.


Feline Immunodeficiency Virus is spread primarily through bite. Kittens contracting the virus from an infected mother are rare, but occasionally kittens are born infected. Generally, kittens that are tested for FIV and are found to be negative can be considered free of the virus, unless they are allowed outdoor contact with other cats.


We strongly recommend testing every cat, whether an adult or kitten, for the FIV virus. Just as with FelV, this is especially important if there are other cats in the household. Ideally, kittens and new adult cats should be isolated from any other cats in the home until a negative FIV test result is achieved. We perform FIV tests with a simple blood test run in our hospital. The test is usually run in combination with the FelV test. In kittens less than six months of age, the results of the FIV test are considered inconclusive. If your kitten is tested for FelV prior to six months of age, we will not report the FIV test result unless a positive result is observed. A positive result at this young age will only be used to encourage owners to keep the new kitten isolated from other family cats until a retest can be performed at six months of age. If the second test (performed when the kitten is six months old or older) is positive, your veterinarian will discuss the consequences for your cat’s health. A negative FIV test in a cat or kitten older than six months serves as a strong assurance that your new feline family member is virus-free.


Unfortunately, there is no vaccine to protect cats from FIV. The only means of prevention is to keep your cat exclusively indoors. Your cat is at greater risk of exposure for both FIV and FelV if:

  • It is allowed outside the house.
  • It is a male cat.
  • It fights with other cats.
  • It has not been neutered.
  • It has not been vaccinated for FeLV.
  • It lives in a multi-cat household.
  • It is an indoor cat, but has contact with an outdoor cat.
  • It has unknown or untested mother.
  • It is from a cattery, pet store, or breeder.

Please ask your veterinarian any questions you have regarding your cat’s health, vaccinations or FIV and FeLV testing.