Feline Leukemia (FeLV) is a highly contagious and deadly disease among cats. Keep reading to learn about the symptoms, diagnosis, and prevention of FeLV.

The Feline Leukemia Virus (FeLV) is a highly contagious virus in the feline community (it can not be spread to humans or species other than cats). It is a different virus from the Feline Immunodeficiency Virus (FIV). Feline Leukemia is caused by a retrovirus; The virus produces an enzyme that allows it to create copies of its own genetic material using the host’s cells.  There are 3 different types of FeLV, 2 stages in the progression of the illness, and several possible symptoms.

Title Photo Credit: Kristin Nador via Flickr

Types of Feline Leukemia:

  1. Feline Leukemia (FeLV) is a highly contagious and deadly disease among cats. Keep reading to learn about the symptoms, diagnosis, and prevention of FeLV.

    An electron micrograph of the Feline Leukemia Virus. Public Domain via Wikimedia Commons

    This type causes immune deficiency in the cat – a problem caused by all 3 types.  Cats with FeLV may develop serious or even fatal illnesses caused by viruses, bacteria, or other infectious materials that a healthy cat would easily fight off.

  2. FeLV-B
    This type of FeLV is the most common cause of cancer in cats. They could develop tumors and other abnormal growths. About 50% of all cats diagnosed with FeLV have FeLV-B.
  3. FeLV-C
    This is the least common type of FeLV. Cats with FeLV-C will develop blood disorders such as anemia.

Stages of the Disease

  1. Primary Viremia.
    When a cat first becomes infected with the virus it will be in the Primary Viremia stage.  The cat may not show any symptoms at all during this stage, but is still capable of infecting other cats. The good news is that at this stage, the cat may still be able to rid themselves of the virus (60% of cats do). A cat may remain in this stage up to 4 months after infection.
  2. Secondary Viremia.
    This stage is reached with the virus has made its way into the bone marrow and other tissues. Unfortunately, once a cat comes to this stage of the disease, it will not be able to rid itself of the virus; They will live with the virus for the rest of their life. When this stage is diagnosed, less than 30% of cats live longer than 3 years.

How Does FeLV spread?

FeLV is VERY contagious. Infected cats can shed the virus in their saliva, nasal secretions, urine, feces, and milk. Cats become infected by contact with infected cats – bite wounds, mutual grooming, sharing food/water dishes, sharing litter boxes, etc. Mother cats can also spread the virus to their kittens in utero or through their milk.

Young kittens are the most at risk for FeLV infection. It seems that older cats develop better ways to fight off the virus.  The risk for infection climbs for cats of any age in multi-cat households and with cats that are allowed outdoors without supervision.


The symptoms of Feline Leukemia are not specific to this disease. More likely, FeLV will be discovered through the symptoms of a secondary illness. There’s no way to definitively tell if a cat has this disease through observation only. If you feel that your cat may have FeLV, visit your veterinarian and get a proper diagnosis. Some symptoms that might be observed include:

  • Feline Leukemia (FeLV) is a highly contagious and deadly disease among cats. Keep reading to learn about the symptoms, diagnosis, and prevention of FeLV.

    Photo Credit: Austin Community College via Flickr

    Progressive weight loss

  • Loss of appetite
  • Abscesses
  • Poor coat condition
  • Fever
  • Diarrhea
  • Seizures
  • Behavior changes
  • Pale gums
  • Eye conditions
  • Upper respiratory infections
  • Urinary tract infections
  • Infections of the skin
  • Enlarged lymph nodes
  • Inflammation of the gums or mouth
  • Aborted pregnancies and other reproductive problems

Diagnosis & Treatment

Feline Leukemia (FeLV) is a highly contagious and deadly disease among cats. Keep reading to learn about the symptoms, diagnosis, and prevention of FeLV.

A snap test showing that a cat is FIV+, but FeLV negative. Photo Credit: Kalumet via Wikimedia Commons

Your veterinarian will have to do a blood test to diagnosis Feline Leukemia. These tests will not give accurate results until 60 days after the initial infection takes place. A snap test can be done quickly right in the veterinarian’s office.  This test will detect both stages of the disease, but it can not determine which stage the cat is in. The IFA test, which is a little more expensive and must be sent out to a lab is very definitive and will only detect the second stage (Secondary Viremia). Discuss your options with your veterinarian as they may want to do other tests as well to rule out other problems.

If your cat has been officially diagnosed with Feline Leukemia, work with your veterinarian on a care plan. Most likely, you will need to bring the cat in for a check-up every 6 months. You will also have to make sure that your cat’s diet is nutritionally balanced. It will be important to protect your cat from harmful bacteria, fungus, mold, etc because of its weakening immune system. Providing a comfortable quiet place for your cat to rest when they are not feeling well is important too.


There is no cure for Feline Leukemia yet. Taking steps to prevent the disease is very important. As it is said, “an ounce of prevention is worth a pound of cure.” Here are a few steps you can take:

  • Get any new cat entering your home tested for FeLV before introducing it to your other cats.
  • House FeLV + cats separately from uninfected cats. Adopting an FeLV+ cat is perfectly fine if they are the only cat in the household or if all of the other cats in the household are FeLV+ as well.
  • Keep cats indoors.  This limits their exposure to infected cats.
  • A vaccine is available, but it is not a cure-all. Even a properly vaccinated cat can potentially become infected through contact with an infected cat. The vaccine will not help a cat that is already infected.
  • Disinfect surfaces (including your skin or clothing) that are exposed to a FeLV-infected cat before exposing a non-infected cat to those same surfaces. The FeLV virus does not live long outside of the cat’s body (only a few hours) and is killed by normal household disinfectants.

Have you ever known a cat with Feline Leukemia?

Sources & Digging Deeper

Feline Leukemia Virus (FeLV) – Cornell University College of Veterinary Medicine

Feline Leukemia Virus – PetMD

A Cause of Immunodeficiency in Cats – Drs. Foster & Smith

Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV) – What’s the Difference? – Dr. Karen Becker, DVM