Feline Leukemia

What is Feline Leukemia?

Feline leukemia (FeLV) is a retrovirus affecting cats. It is not transmissible to humans. After a cat is exposed to the virus it replicates in the oronasal region and then spreads throughout the rest of the body (Collado et al. 2007). There can be two different outcomes at this point. If the cat's immune response is strong enough to completely eliminate the virus then the cat can become FeLV free. If the cat cannot completely eliminate the virus then the virus becomes sequestered in the cat's bone marrow (Collado et al. 2007). Once this happens the cat remains infected with the virus for life.

Common problems seen in feline leukemia positive cats are secondary infections and tumor formation due to the cat's compromised immune system, and severe anemia. Gingivitis is common in feline leukemia positive cats and should be treated with antibiotics before the gingivitis leads to a more serious infection.

How is Feline Leukemia Diagnosed?

A diagnosis for feline leukemia can be made by two different blood tests. The most common test used to screen cats for feline leukemia is the ELISA (enzyme-linked immunosorbent assay) test. This test can be done in your veterinarian's office and the results are usually ready in about 15 minutes. If your cat tests positive for feline leukemia on the ELISA test then most veterinarians will do a second blood test called immunofluorescence assay (IFA). This test usually cannot be done in your veterinarian's office and must be sent to an outside lab. The results are usually back within a few days.

Both tests check for the presence of the FeLV p27 antigen in the blood (Herring et al., 2001), however, the ELISA tests for the presence of free FeLV antigen in the blood serum and the IFA tests for antigen presence in the white blood cells. A positive IFA indicates the bone marrow is affected and that the cat will remain persistently viremic. Also, occasionally a false positive will occur for the ELISA and so if the ELISA is positive for feline leukemia always have the IFA test done before making decisions regarding the cat.

Feline leukemia has an incubation period of about 8 weeks. If you take in a stray who tests negative for feline leukemia it is a good idea to have the cat retested for the virus about 2 months later. This is especially important for strays that have fight wounds when you first have them tested because feline leukemia is commonly transmitted through fight wounds in strays and outdoor cats. A cat that was very recently exposed to the virus before the initial feline leukemia test was done may initially test negative for feline leukemia, but may still be infected, and may test positive two months later. This is somewhat rare, but it does occur.

Treatment and Management of Feline Leukemia

If your cat has been recently diagnosised with feline leukemia he or she can still have a happy life for a time, it will just be shorter than the normal life span for a healthy cat. Try to take comfort in knowing that you are giving your cat the best life possible in the time he or she has left.

Cats infected with the feline leukemia virus can remain healthy for a couple of years, especially if the cat was healthy when the initial feline leukemia diagnosis was made. There are reports of cats living as long as 7 years or more with the virus, but FeLV positive cats usually only live about two more years after the diagnosis is made. If you find out that your cat is positive for feline leukemia please don't let it go outside to infect other cats. You must keep a feline leukemia positive cat indoors only.

Because feline leukemia positive cats have compromised immune systems they sometimes need treatment for secondary infections, such as eye and gum infections. These can usually be treated successfully with antibiotics. Your cat should be examined and treated for any internal or external parasites and have a complete blood count done to determine the status of your cat's health.

Good nutrition is very important. Feed your cat a high quality cat food, such as Hill's Science diet or some other premium cat food, but don't feed your cat semi-moist cat foods containing the ingredient propylene glycol (Cotter, 1991). Propylene glycol shortens the lifespan of red blood cells and may contribute to anemia, which is a serious problem in feline leukemia positive cats.

Some people give their feline leukemia positive cat interferon. This is an immunomodulator and has antitumor effects. In a controlled research study Weiss et al. (1991) found that feline leukemia positive cats that were given interferon had a 75 percent reduction in symptoms. Feline leukemia positive cats are given interferon every other week for seven days, usually for the rest of their life (McCaw, 1985). Interferon can be obtained from your veterinarian for feline leukemia positive cats.

If You Have Other Cats in Your Household

If you have other cats in your household in addition to the FeLV positive cat they should be tested for feline leukemia and if they are negative they should be vaccinated against the virus. The efficacy of the feline leukemia vaccine isn't 100 percent in preventing FeLV infection, but their degree of protection against the virus will be much greater than if they are unvaccinated.

Some veterinarians will suggest housing the feline leukemia cat separately from your other household cats. Depending on your situation and how much room you have at your house or apartment, this may be impractical, especially if the other cats have already been exposed to the FeLV positive cat before the diagnosis was made. In a study of FeLV households, once FeLV was detected only 17 percent of the other cats in the household developed feline leukemia (McCaw, 1995). However, you should have your other cats vaccinated against the virus if you are going to house your feline leukemia positive cat(s) together with your feline leukemia negative cats. Even after being vaccinated there is still some risk to your feline leukemia negative cats. FeLV positive cats shed the virus in their saliva, and so sharing water and food bowls and mutual grooming can result in infection. The virus doesn't survive long outside of the body, but it can live for several hours in a moist environment.

Also, young kittens are much more susceptible to infection from the virus than older cats. If you have young kittens in your household it is best to keep them separated from a feline leukemia positive cat until they are older and their immune system is stronger. This is true even if the kittens have been vaccinated against feline leukemia.

Please note that corticosteroids shouldn't be used on the feline leukemia negative cats in a feline leukemia positive household because if your negative cats are latently infected the steroids might activate the virus (McCaw, 1995).

Our cat Crispin who lost his battle with feline leukemia

Crispin, our dear cat who lost his battle with feline leukemia before his third birthday, but we did have a couple of very good years together even after his diagnosis.


Collado, V. M., Gomez-Lucia, E.,Tejerizo, G.,Miro, G.,Escolar, E., Martin, S., & Domenech, A. (2007). Effect of type I interferons on the expression of feline leukaemia virus. Veterinary Microbiology, 123 180-186.

Cotter,S. M. (1991) Management of healthy feline leukemia virus-positive cats. Journal of the American Veterinary Medical Association, 199, 1470-1477.

Herring,I. P., Troy, G. C., Toth,T. E., Champagne, E. S., Pickett,S. J. P., & Haines, D. M. (2001). Feline leukemia virus detection in corneal tissues of cats by polymerase chain reaction and immunohistochemistry. Veterinary Ophthamology, 4, 119-126.

McCaw, D.(1995). Caring for the retrovirus infected cat.Seminars in Veterinary Medicine and Surgery (Small Animal), 10(4), 216-219.

Weiss,R. C., Cummins, J. M., & Richards,A. B., (1991). Low-dose orally administered alpha interferon treatment for feline leukemia virus infection. Journal of the American Veterinary Medical Association, 199, 1477-1481.