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What is Feline Leukemia Virus (FeLV)? Vet Advice

Feline Leukemia Virus (FeLV) is a virus that infects cats and weakens their immune system. It can cause different types of cancers, blood disorders, and other diseases in cats. FeLV is one of the most common and serious infectious diseases in cats worldwide.

How is FeLV transmitted?

FeLV is spread mainly through saliva from one cat to another. Cats can get infected by biting, grooming, sharing food or water bowls, or using the same litter box with an infected cat. Kittens can also get infected from their mother before birth or during nursing.

What are the signs of FeLV infection?

FeLV infection can have different stages and outcomes depending on the cat’s age, health, and immune response. Some cats can fight off the virus and clear the infection, while others can carry the virus for life and develop diseases related to FeLV.

Some of the signs of FeLV infection are:

  • Loss of appetite
  • Weight loss
  • Poor coat condition
  • Enlarged lymph nodes
  • Fever
  • Pale gums
  • Mouth or gum inflammation
  • Skin, urinary, or respiratory infections
  • Anemia (low red blood cell count)
  • Lymphoma (cancer of the lymph nodes)
  • Leukemia (cancer of the white blood cells) 

Some cats may not show any signs of FeLV infection for a long time, but they can still spread the virus to other cats or develop diseases later in life.

How is FeLV diagnosed?

FeLV can be diagnosed by testing a blood sample from the cat. There are different types of tests that can detect different stages of FeLV infection. The ELISA test, which identifies the FeLV antigen (a protein produced by the virus) in the blood, is the most commonly used test. A positive ELISA test means that the cat is infected with FeLV and can spread the virus to other cats.

How is FeLV diagnosed
How is FeLV diagnosed?

Another test is the PCR test, which detects the presence of FeLV DNA (the genetic material of the virus) in the blood or other tissues. A positive PCR test means that the cat has FeLV DNA integrated into its own DNA and may develop diseases related to FeLV in the future.

How is FeLV treated?

There is no cure for FeLV infection, but there are ways to manage it and improve the quality of life of infected cats. Some of the treatment options are:

  • Antiviral drugs: These drugs can reduce the amount of virus in the blood and slow down the progression of FeLV-related diseases. However, they are not widely available, expensive, and may have side effects.
  • Immunomodulators: These drugs can boost the immune system and help fight off secondary infections. They may also reduce the risk of developing cancers related to FeLV.
  • Chemotherapy: This is a treatment for cancers caused by FeLV. It involves using drugs that kill cancer cells or stop them from growing. Chemotherapy can shrink tumors, relieve pain, and prolong survival.
  • Supportive care: This includes providing good nutrition, hydration, parasite control, pain relief, and antibiotics for infections. Supportive care can help improve the cat’s comfort and well-being.

How can FeLV be prevented?

The best way to prevent FeLV infection is to vaccinate cats against it. There are different types of vaccines that can protect cats from FeLV infection or reduce its severity. However, no vaccine is 100% effective, and some cats may still get infected despite being vaccinated.

Other ways to prevent FeLV infection are:

  • Testing: All cats should be tested for FeLV before being introduced to a new home or a multi-cat household. Cats that test positive should be isolated from other cats or kept with other FeLV-positive cats only.
  • Neutering: All cats should be neutered to prevent unwanted pregnancies and reduce roaming and fighting behaviors that can increase the risk of FeLV transmission.
  • Indoor living: Cats that live indoors are less likely to encounter infected cats or other sources of infection than outdoor cats. Indoor living also reduces exposure to other hazards such as traffic, predators, or poisons.

US-Approved Cat Treatment

In 2006, a new cat treatment called Lymphocyte T-cell immunomodulator (LTCI) got a special nod from the United States Department of Agriculture. It’s made and distributed by T-Cyte Therapeutics, Inc.

LTCI is designed to help cats with feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV), and the problems these viruses bring, like low white blood cells, infections, anemia, and more. The good news is, it seems to be very safe for cats.

LTCI does a great job at controlling a type of white blood cell and making it work better. It’s been tested in animals and found to boost these cells and help produce a helpful substance called Interleukin 2.

LTCI is made of one special kind of protein. It’s positively charged and super pure, made from cow cells. This protein is very much like proteins found in other animals and is a solid 50 kDa protein with an isoelectric point of 6.5. It comes as a tiny 1-microgram dose that you mix with sterile stuff to give your cat a shot.

European-Approved Cat Treatment

In Europe, they’ve got a treatment called Interferon-ω (omega), and it goes by the name Virbagen Omega. It’s made by a company called Virbac. When used on cats with FeLV who aren’t in the very last stages (usually older than 9 weeks), it has made a big difference. For cats not dealing with anemia, it has cut the chance of dying by about 20% from the normal 50% rate. This has improved how we help cats with feline leukemia in Europe.


Feline Leukemia Virus (FeLV) is a serious disease that affects many cats around the world. It can cause various cancers, blood disorders, and immune problems in cats. You can diagnose FeLV with blood tests and treat it using antiviral drugs, immunomodulators, chemotherapy, and supportive care. To prevent FeLV, you can vaccinate your cats, test them, neuter them, and keep them indoors. FeLV-infected cats can still live a happy and comfortable life with proper care and management.

Frequently Asked Questions (FAQs)

  1. What are the symptoms of feline leukemia virus?

    Cats with feline leukemia virus can show various symptoms like loss of appetite, weight loss, lethargy, fever, and respiratory issues. They might also have recurring infections, gum problems, or even behavioral changes.

  2. How long can a cat live with feline leukemia?

    Cats with feline leukemia can have varying lifespans. Some might live for a few years, while others may live longer. It depends on their overall health and how well the virus is managed.

  3. Is feline leukemia virus fatal?

    Feline leukemia can be a serious and sometimes fatal disease. It weakens a cat’s immune system, making them more vulnerable to other illnesses. With proper care, some cats can live a good quality of life, but sadly, it can be fatal.

  4. Is feline leukemia actually cancer?

    Feline leukemia is a viral infection, not cancer. However, it can sometimes lead to certain types of cancer, like lymphoma. It’s a complex disease that affects a cat’s health in various ways.

  5. How is feline leukemia virus diagnosed in cats?

    Feline leukemia virus can be diagnosed through a blood test, most commonly the ELISA test, which detects the presence of the virus’s antigen in the blood. If your cat is at risk or showing symptoms, consult your veterinarian for testing and guidance.

References, sources, and more:

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