Home » Pet Health » Feline Infections and Viruses » How is FeLV Diagnosed and Treated?


Feline leukemia virus (FeLV) is a common virus that infects cats. Most cats’ immune systems can fight the infection. But if your cat shows the following symptoms, it may have FeLV: fatigue, fever, wheezing, sneezing, diarrhea, sores on the skin, and inflammation in the mouth and lymph nodes. However, these could be signs of other issues. Since a FeLV infection could lead to cancer if untreated, it is best to have your vet determine if your has FeLV.


Your vet will test your cat’s blood for markers of FeLV. The presence of those markers confirms that your cat is FeLV positive. The cat will remain FeLV positive for its lifetime and can pass the virus on to other cats.


Currently, therapies such as vaccines may help reduce viral replication and spread, improving the condition of infected cats. Like any treatment, there may be side effects to look for, but your vet can tell you what to expect with a vaccine and how to manage potential side effects.

Additionally, studies are underway to look for experimental drugs, such as those that fight against viruses in the same class as FeLV and immune-boosting therapies. Since FeLV suppresses the immune system, your cat may have difficulty fighting off other infections. Therefore, vets managing FeLV-positive cats usually treat diseases that arise due to a weak immune system, such as bacterial infections.

Although there is currently no therapy for FeLV, your cat can have a good quality of life for years after diagnosis. Reports suggest that FeLV-infected cats that are well-cared for and treated for symptoms of the virus are likely to have an improved and extended life.

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Last Updated: August 3, 2022

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The following sources were referenced to write the content on this page:  

de Mari, K, Maynard, L, Sanquer, A, Lebreux, B & Eun, HM 2004, ‘Therapeutic effects of recombinant feline interferon-omega on feline leukemia virus (FeLV)-infected and FeLV/feline immunodeficiency virus (FIV)-coinfected symptomatic cats’, J Vet Intern Med, vol. 18, no. 4, pp. 477-482.

Greggs, WM 3rd, Clouser, CL, Patterson, SE & Mansky LM 2011. ‘Broadening the use of antiretroviral therapy: the case for feline leukemia virus’, Ther Clin Risk Manag, vol. 7, pp. 115-22.

Hartmann, K 2012 ‘Clinical aspects of feline retroviruses: a review’, Viruses, vol. 4. No. 11, pp. 2684-2710.

Hofmann-Lehmann, R, Tandon, R, Boretti, FS, Meli, ML, Willi, B, Cattori, V, Gomes-Keller, MA, Ossent, P, Golder, MC, Flynn, JN & Lutz H 2006, ‘Reassessment of feline leukaemia virus (FeLV) vaccines with novel sensitive molecular assays, Vaccine, vol. 24, no. 8, pp. 1087-94.

Stuetzer, B, Brunner, K, Lutz, H & Hartmann, K 2013, ‘A trial with 3′-azido-2′,3′-dideoxythymidine and human interferon-α in cats naturally infected with feline leukaemia virus’, J Feline Med Surg, vol. 15, no. 8, pp. 667-671.

The Pet Cancer Foundation’s medical resource for pet owners is protected by copyright.

For reprint requests, please see our Content Usage Policy.