Feline Leukemia Virus

Feline leukemia virus (FeLV) infection is one of the most serious diseases affecting cats and other small animals. The virus is spread from cat to cat in saliva, through bite wounds, by contact, and sharing feeding bowls or litter boxes. Most at risk are cats that are allowed to spend time outdoors. Kittens are especially susceptible to this infection. The virus is present in many apparently healthy cats. Blood tests are available to determine if a cat is infected with the virus. The disease can spread among animals, however, there is no proved connection with leukemia in humans.

Routes of Infection

Feline leukaemia virus infection in cats results mainly from exposure to infectious saliva and nasal discharge. Bites from infected cats are a highly efficient method for transmission for FIV and FeLV due to high levels of virus in the saliva. Recent studies have shown that fecal shedding of feline leukemia virus in the feces of infected cats can be a source of infection. Non-infected cats exposed to these feces showed that infection through feces took place. These findings prove that fecal shedding of FeLV plays a role in transmission, but it is probably of secondary importance in viral infections. Nevertheless, sharing of litter pans by susceptible and infected cats could increase the environmental infectious pressure and appropriate measures should be taken to avoid unnecessary viral exposure.

Signs vary depending on the particular form of the disease. Signs of the neoplastic form often include enlargement of the lymph nodes, lethargy, fever, vomiting, weight loss, labored breathing, jaundice, pale gums, general weakness and diarrhea. The non-neoplastic form is characterized by persistent fever, weight loss, discharge from the nose, sores around claws and inflammation of the gums.


The vaccination is recommended only for cats considered at risk for FeLV infection which include those allowed outdoors, those living in shelters, or those living in situations where new cats enter the environment frequently. Cats can catch feline leukemia only from direct contact with an infected cat. Mother cats can also pass it to their kittens. The best way to protect your cat against feline leukemia is to prevent exposure to possibly infected cats, as the vaccine isn't perfect and doesn't confer protection on all vaccinated cats. At-risk cats should be vaccinated every year. Initially, kittens are given two doses of vaccine three-to-four weeks apart, starting at age eight weeks. Because infected cats may appear to be healthy, it is recommended to have any new cats tested before bringing them home.


  1. Fecal shedding of infectious feline leukemia virus and its nucleic acids: A transmission potential.Gomes-Keller MA, Gönczi E, Grenacher B, Tandon R, Hofman-Lehmann R, Lutz H. In: Vet Microbiol. 2008 Aug 22.
  2. The kinetics of feline leukaemia virus shedding in experimentally infected cats are associated with infection outcome. Cattori V, Tandon R, Riond B, Pepin AC, Lutz H, Hofmann-Lehmann R. In: Vet Microbiol. 2008 Jul 25.
  3. 2008 American Association of Feline Practitioners' feline retrovirus management guidelines. Julie Levy, Cynda Crawford, Katrin Hartmann, Regina Hofmann-Lehmann, Susan Little, Eliza Sundahl and Vicki Thayer. In: Journal of Feline Medicine & Surgery, Volume 10, Issue 3, July 2008, Pages 300-316.

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