feline leukemia

Leukemia in Cats, Kittens

Feline Leukemia is a cancer of the cat's lymphocytes (white blood cells). It is caused by the Feline Leukemia Virus and is a common cause of illness and death in cats. Feline Leukemia can be transmitted from cat to cat via bodily fluids, primarily saliva. The presence of the virus can be detected via blood tests. Prevention often involves proper vaccination.

Kitten with Feline Leukemia (FELV)

Hi Simba, I recently found an adorable kitten amp; am already in love with it.
Yesterday I took it in for its first vet visit. The vet said it tested positive for feline leukemia(!) however we will test again in 3 weeks to be sure.

I am not going to have the kitten put down no matter what the test shows. Please tell me more about Feline Leukemia so we know what to do.
Dear Donna G,
How wonderful you have taken this little gal into your home. She is lucky to have a caring person as you to watch our for her. Here is a little background on Feline Leukemia (FeLV)

As you know, FeLV is a common cause of illness and death among cats.


Feline Leukemia is a disease caused by the Feline Leukemia Virus (FeLV). The Leukemia itself is a cancer of the cat's lymphocytes (white blood cells). What FeLV does is it produces an enzyme which permits it to make and insert copies of its genes into cells it infects. When it infects the white blood cells it suppresses the immune system.


Contact with bodily fluids from an infected Cat. Examples of transmission are contact with saliva from mutual grooming, biting, milk, urine, feces...In some cases contact with an infected cat's food dishes (not as common).

The good news is that FeLV is not stable in that does not live long outside of the body...a few hours maybe in a normal house.

Infected mother cats usually pass on the virus to their kittens, which often results in early death or even abortion.

Note that not all cats exposed to FeLV become infected with the virus since some cats may not be exposed to sufficient quantities of the virus and / or they are able to defend themselves via an effective immune response that eliminates the virus.

Age is also important. The younger the kitten the more susceptible he/she is to getting sick.


FeLV is a very common cause of cancer when it infects the blood cells (see above) and it also causes blood disorders that adversely affect the immune system...Cats with weak immune systems (see FIV) are susceptible to infections that they would otherwise easily resist.

Anemia is another common cause of death in FeLV kitties, (affects nearly 25% of infected cats). What happens is that the red blood cell in the bone marrow or in the blood stream becomes infected by FeLV which causes depletion and anemia.

Unfortunately, nearly 90% of infected cats die within 3 to 3 1/2 years after diagnosis. About half of deaths are caused by immune system suppression in which an otherwise beatable infection kills. Signs to watch (mthough not exclusive to Leukemia) for include:

There are 2 stages in FeLV infection.
  • First State / Primary viremia is an early stage of infection. This is when the cat's immune system fights FeLV. If successful, an effective immune response will eliminate the virus from the bloodstream and stop the disease from reaching State 2

  • Stage 2 / Secondary viremia is a later stage where the cat has a persistent infection of the bone marrow and other internal tissue. When the cat is in stage 2 it is no longer able to eliminate the virus and will be infected for the rest of its life.


Diagnosis of FeLV infection is straightforward, as the virus is present in the blood and within infected cells in the blood, bone marrow and elsewhere in the body. The tests (there are two) detect a protein component of FeLV as it circulates in the bloodstream.


There is now an widely used vaccine for preventing Feline Leukemia. There is both an injectable and a needle-less version of the feline leukemia vaccine. Note that there have been instances where the vaccine has resulted in injection-site tumors. Please discuss with your vet.

If your cat has been infected with FeLV the onset of symptoms will depend on the strength of his /her immune system. Your best bet is to continue being the loving and supportive parent and to keep the cat away from uninfected cats. - Simba

Leukemia in a New Family Kitten

Dear Simba,
My family and I just got a 6 week-old kitten last night. We took it to the vet today to get it checked out and they ran a blood test. From the blood test we found that the kitten may have leukemia, we will not know for sure until Monday.

My question is what do we do next if the kitten has this problem. We are totally new to the cat world and are trying to learn as we go. From people I have talked to this test is somewhat unreliable. I have been told that if the kitten has leukemia it still will live a long life. If this is true what do we need to do to keep as health as possible? I have a 4 and 2-year-old that are getting attached quick and the less pain for everyone the better, that is including the kitty too. Kevin W

Dear Kevin W,
I certainly hope that as I write this your little kitten is free and clear of Feline Leukemia. If he is not, do not give up just yet. Although he is against the odds, your little friend may make it after all. Given your young children and your wish to avoid causing them undue pain, you may want to give the kitten to a foster care home where the little guy can be cared for. There are many loving folks out there that will open their hearts to needy kittens, if only for a short time. Keep me posted. Simba

Surviving Feline Leukemia: Sheba's Story

Dear Simba,
I read the letters on FeLV and wanted to add something. I am glad you urged your readers to wait and see if their cats are okay. My cat Sheba caught FeLV at an early age. Sheba was a year old when we found her. She is now close to her 9th birthday! Over the years, we have had only minor problems with FeLV - Sheba had one mouth wound that required surgery to heal, and 2 decaying back teeth required removal. that is it! We have been very lucky, and I am so glad that I listened to my heart and did not put Sheba to sleep when we learned she was FeLV+. I want to encourage fellow cat lovers to give FeLV+ cats a chance! Do not put your cats 'to sleep' unless s/he is in severe pain or discomfort. Thanks for letting me share Sheba's story! Michelle in Houston

Thanks for the note. I am glad you and Sheba are doing well! Simba

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