Guide to the Feline Leukemia Virus (FeLV)

"The Feline Leukemia Virus (FeLV) usually affects young cats or kittens. Since the mid 1980's it has been prevented with a vaccine. There is no known treatment for Feline Leukemia. Symptoms gradually appear as the immune system weakens such as lymphoma (neoplastic disease). Some cats can fight the virus when it is in its early stages. The risk is from other diseases such as cancer and infection that can form when the immune system isn't working properly. The disease can be spread through mutual grooming to other cats. In cats that get the disease, there are three outcomes; 1) recovery, 2) eventual infection (possibly in years as infection in the bone marrow eventually cause the disease) or 3) persistent infection. It is possible for a cat to recover or stay healthy for a period of time, only to get sick from a secondary infection (another infection made possible by the weakened immune system). Sick cats should remain indoors to avoid being exposed to infections and away from other cats."

Feline Leukemia is are caused by what is known as a retrovirus. The disease is also called FeLV. A retrovirus spreads by inserting something called an enzyme into healthy cells. The infection is found in 2% - 3% of all cats and is the leading cause of cancer in cats.

The disease is spread from cat to cat through:

Leukemia is a cancer that spreads in the tissues of the body that create blood. The condition causes the white blood cells to multiple abnormally, a problem interferes with the immune system. This makes it easier for infections caused by bacteria, fungus, other viruses and protozoa to take hold. It also can cause disorders of the blood.

There is no evidence that the disease cannot be passed from cat to human. That said, a cat that is susceptible to other illnesses due to a weakened immune system could be a risk to people depending on the disease.

Stages of Cat Leukemia Symptoms

The disease is often referred to by different names depending on the stage:

Cats Likely to Be Infected

Outdoor cats or if your indoor cat spends some time outdoors she can be susceptible to the disease from bites from an infected cat. If a cat is infected and gives birth, the kittens will be infected.

Feline Leukemia Symptoms

In most cats, symptoms of FeLV will not appear for two weeks. Symptoms start of appear slowly. It might seem like you cat is getting sick more often than usual.

According to the Cornell University College of Veterinary Medicine, specific feline leukemia symptoms include:

Diagnosis of Leukemia in Cats

Your veterinarian will administer a blood test (CBC) that detects a protein that exists in the virus. The tests are called ELISA (results in the vets office) or IFA (must be sent to an outside laboratory).

Both tests might be needed for a certain diagnosis.


There is no known treatment for cat leukemia virus. The threat is often not from the virus itself, but from other infections and diseases that form due to a weakened immune system. Herbal and natural remedies with ingredients selected to support the systems of cats with cancer such as PetAlive C-Caps could help to maintain a better quality of life. Discuss this and all alternative approaches with your veterinarian.

Secondary infections can be treated with antibiotics. Any lymphoma or neoplasms can be treated with radiation or chemotherapy depending on the tumor.  Some cats respond to a treatment called human recombinant erythropoitin.


Be sure to vaccinate your cat from FeLV (administered to only FeLV cats). The vaccine does not work in cats that are already infected. It may not work in some vaccinated cats.

Since exposure to the virus usually occurs from one cat to the next, prevention starts with isolation. This includes keeping your cats away from other cats when outside and when adopting cats, make sure that they are test.

Prognosis of Infected Cats

A cat can live with cat leukemia for several years. Persistently viremic cats are likely to develop overt disease within a
relatively short period after infection, with about 1/3 of all infected cats dying each year after infection. As the immune system is weakened over time and cat leukemia symptoms start to appear, your cat could become increasingly ill.


Update on feline retroviral infections
Leah A. Cohn
DVM, BS, PhD, Dipl ACVIM, Columbia, USA

Feline Lymphosarcoma (Lymphoma, LSA)

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