Signs Of Feline Leukemia

Before setting out the signs of feline leukemia a little background information may help. I am also making the presumption that people searching for information about feline leukemia are in fact searching for information about the feline leukemia virus, which causes cancer and it is referred to as an oncogenic RNA virus. An RNA virus is a virus that has RNA (ribonucleic acid) as its genetic material1. Oncogenesis is the process of malignant transformation leading to the formation of a cancer or tumor (tumorigenesis). It is characterized by a progression of changes on cellular and genetic level that ultimately reprogram a cell to undergo uncontrolled cell division, thus forming a malignant mass1.

Above: the feline leukemia virus (Wikipedia Commons file)

The cancer caused is lymphosarcoma. 90% of cats with this cancer carry this virus. However only a small percentage of cats with persistent viremia develop a virus related cancer3. Viremia means: a medical condition where viruses enter the bloodstream and hence have access to the rest of the body1.

The virus is known as FeLV. FeLV infects cats throughout the world including small wildcat species.

The virus survives for only minutes to hours outside the body. This means that infection is by direct contact between cats is necessary to transmit the disease (or in utero transmission – leads to fetal death 80% of time). This also means that the highest infection rates are in crowded colonies or groups (e.g. colonies of urban feral cats).

Infected cats become carriers as they are unable to rid themselves completely of the infected cells2. Cats that are viremic (have the infection in their blood stream) spread the virus through:

  • saliva – e.g mutual grooming, licking, biting, sharing feeding bowls
  • respiratory secretions
  • faeces – sharing litter boxes
  • urine

Most infected adults are less than 3 years old. Older infected cats have either died or combated the disease.

There are four outcomes following infection2:

All catsVirus infects lymphatic tissue (lymph nodes). Virus present in blood stream. Cat sheds virus.
1. 30% cats successfully fight of diseaseCats develop immune response.  Disease does not progress. Virus eliminated.
2. Unknown number of  cats develop immunity but carry diseaseVirus remains in body of cat but it is not shed to other cats. Most of these cats eventually eliminate disease.
3. 30 – 40% of cats latently infectedLate immune reaction. Virus does not spread in body. No shedding of virus to other cats. Mothers transmit disease to kittens via milk.
4. 30 –40% of cats actively infectedInfection progresses. Poor prognosis. Most die within 3 years

Signs of Feline Leukemia2|3

StageSigns of Feline Leukemia
Initial infection
  • These last for 4 months or 2 – 16 weeks:
  • non-specific signs
  • mild illness
  • apathy
  • vomiting
  • constipation
  • enlarged regional lymph nodes
  • low grade fever
  • anorexia
  • anemia
  • pale mucous membranes
  • weight loss
  • transient leukopenia (an abnormally low number of white blood cells in the circulating blood)
Stage 2: Peristent infection
  • Occurs months to years after initial stages:
  • FeLV depresses the cat’s immune system allowing other diseases to develop such as:
  • feline infectious peritonitis,
  • feline infectious anemia,
  • feline viral respiratory
  • disease complex,
  • toxoplasmosis
  • cystitis
  • periodontal disease
  • bacterial infections
  • anemia and spontaneous bleeding due to bone marrow suppression
  • jaundice (yellowing skin and white of eyes):
  • a small percentage of cats develop cancer of which lymphosarcoma is most common and leukemia (rapid uncontrolled growth of white blood cells.

  • for kittens who received the disease from their mother:
  • fading kitten syndrome
  • still birth

As can be seen the signs of feline leukemia are wide because FeLV leads to a wide range of other diseases.

Related pages – further information

FeLV infected cats can live for a relatively long time and therefore need homes. These are adoptable FeLV cats. This page: Adoptable FeLV cats also covers information about testing for FeLV and has an input page for people to advertise FeLV cats for adoption.

Signs of Feline Leukemia – Notes:

1. Wikipedia authors

2. The Cat, Its Behaviour, Nutrition & Health by Lind P Case pages 198 – 202.

3. Cat Owner’s Home Veterinary Handbook by Drs Carlson and Giffin  pages 62 – 64.

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Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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  • Has anyone heard of RetroMAD1 in Malaysia, or Interferon Omega for treating cats with feline leukemia? I'm presently treating my cat and kittens with LTCI, which is helping.

      • Hi. My cat got some viral infection. And now the doctors are giving him RetroMAD1. They only started today. Have you hear anything about this medication?
        Thank you so much

        • Christina where are you located? I had to tell my Vet about RetroMAD1 and while he was EXTREMELY skeptical that such a FeLV drug existed he let me order it to his office. In the words of my Vet my kitten had at most, 10 days to live. My Vet is a great guy who loves animals but it sure was great watching him eat crow as my kitten is now a healthy full grown cat. She has yet to test negative for FeLV but the virus is slowly being killed off by the RetroMAD1 and she is symptom free. She might have even been one of the worst case kittens to be treated with RetroMAD1. The fact that she made it past the 10 day death sentence and is living a normal life a year and two months later is all the proof my Veterinarian needs to retract his statement and say "You were right this stuff works, i'm more than amazed"

          • I too live in the USA and can contest to this wonder drug RetroMAD1. I have a 3 year old FeLV cat who just started RetroMad1 three days ago. I have experienced the same amazing positive results! My cat has lots more energy, appetite has increased, and sleeping less since on the drug. Christina, just curious if your cat is still doing well? Have you had to administer more RetroMAD1 since the fist initial treatment? I'm curious how long they remain symptom free. Thank you!

  • The photo that you are showing of the cat's eye is what drew me to this site. My cat has cancer of the kidneys, and began chemo two weeks ago.

    Just yesterday, we noticed a spot on his eye that looks just like the above photo. Can you tell me more about this condition? Is it tied to the cancer, or bleeding in the eye? Any information you can share would be much appreciated. We are in the midst of another snowstorm, and cannot get him out to the vet today.

    • Amanda, sorry to hear about your cat's poor health. There are many pages on FeLV on PoC. It is a big subject. If you click on the link below you'll be taken to a list of articles:

      List of articles

  • my 6month old cat developed some lumps in his neck and leg I took him to the vets they told me his got cancer I had to have put down I only had him 4months I want to know how did he got it and how long was it in his body I miss him so much he was the sunshine of my life

    • Hi Jamilla, thanks for visiting. I think you'll find that we don't fully understand cancer yet either in animals or humans so we don't know how it starts except to say cancer in cats is at least partly related to feline leukaemia and FIV. Feline leukemia virus accounts for about 50% of all internal cancers in cats.

      It was probably present for quite a while to develop into lumps. Very sorry to hear of your loss.

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