What is Feline Leukemia Virus (FeLV)?

Feline Leukemia Virus (FeLV) is a common infectious disease in cats and most prevalent in environments where there are a lot of cats, like a multi-cat household and where feral cats are living in a free-roaming or unowned environment.

Signs and Symptoms of FeLV

The signs and symptoms of FeLV vary greatly depending on what cells are infected. Some cats may show mild symptoms, but many cats remain without noticeable symptoms altogether. Some signs may include:

Cat liying on the top of a couch at home
  • Fever
  • Loss of appetite
  • Weight loss
  • Lethargy
  • Poor coat condition
  • Enlarged lymph nodes
  • Pale gums
  • Infections of the skin, bladder, and upper respiratory
  • Reproductive problems in unspayed females

Eventually, FeLV-associated diseases will arise which can include:

  • Anemia
  • Liver disease
  • Intestinal disease and reproductive problems
  • Lymphoma or leukemia
  • Chronic respiratory infections
  • Chronic gingivitis and stomatitis (inflammation of the gums and mouth)
  • Poor healing of wounds and abscesses

How is FeLV Transmitted?

  • FeLV is transmitted in the saliva, feces, milk, and urine of an infected cat (the most common route is through saliva). Transmission occurs through grooming, licking, biting, sharing dishes and litter pans, and may occur during pregnancy or nursing from an infected mother to kitten.
  • Close cat-to-cat contact is required to transmit the disease. FeLV can also be transmitted through a blood transfusion.
  • Young cats, especially those under 4-6 months of age, are the most susceptible to FeLV since their immune systems are not fully mature.
  • FeLV cannot be transmitted to people, dogs, or other animals.


FeLV is diagnosed by a simple blood test available at most veterinary practices. There are two types of blood tests that are commonly used for diagnosis:

  • ELISA (enzyme-linked immunosorbent assay) This test identifies FeLV proteins in your cat’s blood and can identify cats with early infections.
  • IFA (indirect immunofluorescent antibody assay) This test must be sent out to a diagnostic laboratory and can detect when the disease has progressed into the secondary stage. Generally, cats with a IFA-positive test result have a poor long-term prognosis.

All new cats or kittens should be tested, as well as any cats that may have been exposed to a known FeLV-infected cat, cats with outdoor access, and any cats that are ill, regardless of whether they have tested negative in the past. Due to the nature of the virus, after exposure an infected cat may not test positive for about 60 days.

Vaccination for FeLV

  • Vaccination against FeLV is recommended for all cats, especially cats with access to outdoors, cats living with known FeLV-infected cats, and in multi-cat environments.
  • FeLV vaccination is also recommended for all kittens due to their increased susceptibility to the virus.

Treatment and Management

  • Unfortunately, there is no cure for FeLV. If your cat tests positive for FeLV and he has a progressive infection, your cat will remain infected for the remainder of his life. A FeLV vaccination is not beneficial if your cat is already infected.
  • You should keep your FeLV infected cat indoors and your cat should be neutered.
  • By partnering with your veterinarian, you can help your cat feel well for as long as possible and help protect them from secondary infection. Your veterinarian will help you to manage your cat’s condition, including the symptoms and any FeLV-associated diseases that may develop.