What happens when a cat has feline leukemia

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Tatiana, a Cat With FeLV
Tatiana, A Cat With FeLV Photo Credit: © About.com Member Nuria Rodriguez

FeLV (Feline Leukemia Virus) and FIV (Feline Immunodeficiency Virus) are both in the retrovirus category, the same type of virus responsible for HIV and some forms of human leukemia. Although somewhat similar, neither FeLV nor FIV are considered to be Zoonotic diseases, i.e. humans cannot contract HIV or Leukemia from cats with FIV or FeLV, (nor can cats contract the feline forms of the latter diseases from a human with HIV or Leukemia).

According to the AAHA (American Animal Hospital Association) Feline leukemia (FeLV), a widespread, incurable virus that typically suppresses a cat’s immune system, is the most common cause of cancer in cats. FeLV is species-specific, so humans and dogs are not at risk.

Since FeLV+ and FIV+ cats can carry several other contagious diseases, it is recommended that certain people who are immunocompromised avoid contact with those cats.

cat looking at top
cat looking at top

How FeLV is Spread

Although the FeLV virus has a limited lifespan outside the body of only two or three hours, it can still be spread in a number of ways:

  • To fetuses in the mother cat's womb
  • To nursing kittens, through the mother's milk
  • Through saliva (bites, mutual grooming, and sometimes shared food dishes)
  • Through nasal secretions - rubbing noses or through mutual grooming
  • Sometimes through urine and feces by shared litter boxes or using the same areas outdoors to leave body waste

Prevention of the Feline Leukemia Virus

Although a FeLV vaccine is available, it is not considered to be a Core Vaccine. It falls into a special category, and the AAFP(Association of Feline Practitioners) does not recommend it routinely, but does recommend an initial shot for all kittens, and recommends it for cats at high risk (indoor-outdoor cats). The reason for these recommendations is the possibility of VAS (Vaccine-Associated Sarcoma), which can occur at the site of the injection. Further, the protocol for giving the FeLV vaccine is in the left rear leg, to allow for amputation in case of VAS.

brown tabby cat close-up photography
brown tabby cat close-up photography

Symptoms of FeLV

Some of the symptoms are similar to several other diseases, and, if not diagnosed early, may become progressively worse over a period of months or even years. They include, but are not limited to:

  • Lethargy
  • Dull, rough coat
  • Painful oral disease, including gingivitis and stomatitis, leading to:
  • Poor appetite, resulting in a slow but steady weight loss
  • Pale gums, due to anemia

Diagnosing FeLV

There are two blood tests to diagnose FeLV:

white and black kitten
white and black kitten
  1. ELISA
    The ELISA test can be done in your veterinary clinic and will determine whether there is FeLV virus in the blood. The initial state of FeLV is called Viremia, literally, virus in the bloodstream. Some cats with healthy immune systems can kick FeLV in that stage, and remain free from FeLV, with the virus leaving their bloodstreams. Your veterinarian will likely request a second ELISA test a few months later. If that test remains clear, your cat will likely remain free from FeLV for life.
  2. The IFA test must be sent out to a laboratory, and your veterinarian might want to order it to confirm the positive results of a second ELISA test. The IFA test will only detect the Viremia stage of the virus. Therefore, a cat who tests positive with the IFA will likely be infected for life.

Treatment of FeLV+ Cats

Like FIV, FeLV attacks the immune system, and death often occurs from a hitchhiker disease, such as infection, rather than from the retrovirus itself.

Potential Hitchhiker Diseases:

short-coated white and black cat sitting on gray metal box
short-coated white and black cat sitting on gray metal box
  • FIP (Feline Infectious Peritonitis)
  • Cancer, such as Lymphoma
  • Other secondary infections, which might be fairly benign when diagnosed and treated promptly in normal healthy cats, including URI's (upper respiratory infections, UTI's (urinary tract infections, such as FLUTD), fungal infections, ringworm, or toxoplasmosis, the latter normally fairly mild in cats to the point of being non-detectible.

Since there is no known treatment for FeLV itself, normal treatment will be confined to those secondary diseases which have attacked the cat's weak immune system.

Experimental Therapy:

greyscale photography of cat beside faucet
greyscale photography of cat beside faucet
white and brown long fur cat with green and red rose on head
white and brown long fur cat with green and red rose on head

Some veterinarians are willing to prescribe certain homeopathic or natural therapies for cats with the FeLV virus. Please do not medicate your cat without consulting with your own veterinarian first, and expect your veterinarian to carefully monitor these therapies. Two of the most commonly-prescribed therapies are:

  • Human Interferon Alpha:
    A veterinary prescription is supplied, and the liquid is given orally. There are potentially harmful side effects, and the effectiveness may be lost within a period of weeks.
  • L-Lysine:
    Available over-the-counter at some pet food stores or online. L-Lysine comes in a powder form to be mixed with food; as a gel, and as flavored treats. I am currently giving one of my cats L-Lysine treats daily for an unrelated condition. However I received them from my veterinarian, and I urge you to consult with your veterinarian before purchasing L-Lysine in any form.

The Ultimate Prognosis

While some treatments may buy time by curing secondary disease, and others may make the cat's day-to-day life more comfortable, the sad truth is that, at the present time, FeLV is considered a fatal disease and the cat will die sooner or later. This is difficult to accept, but there are no guarantees in life, nor can any of us foretell the future.


The author of this article is not a veterinarian. Your own veterinarian should always be your first source for treatment and care advice for a sick cat, regardless of the nature of the illness. This article is meant only to give you a starting place to do your own research so you can make an informed decision, should it ever become necessary.