Feline Leukemia Vaccine
Feline leukemia virus (FeLV) is one of the most common infectious diseases in cats, affecting between 2 and 3% of all cats in the United States and Canada. Infection rates are significantly higher (up to 30%) in cats that are ill or otherwise at high risk (see below). Fortunately, the prevalence of FeLV in cats has decreased significantly in the past 25 years since the development of an effective vaccine and accurate testing procedures.
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Cats persistently infected with FeLV serve as sources of infection for other cats. The virus is shed in saliva, nasal secretions, urine, feces, and milk of infected cats. Cat-to-cat transfer of the virus may occur from a bite wound, during mutual grooming, and (rarely) through the shared use of litter boxes and feeding dishes. Transmission can also take place from an infected mother cat to her kittens, either before they are born or while they are nursing. FeLV does not survive long outside a cat's body – probably less than a few hours under normal household conditions.
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Cats at greatest risk of FeLV infection are those that may be exposed to infected cats, either via prolonged close contact or through bite wounds. Such cats include cats living with infected cats or with cats of unknown infection status, cats allowed outdoors unsupervised where they may be bitten by an infected cat, and kittens born to infected mothers.
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FeLV adversely affects a cat's body in many ways. It is the most common cause of cancer in cats, may cause various blood disorders, and may lead to a state of immune deficiency that hinders a cat's ability to protect itself against other infections. Because of this, disease that usually do not affect healthy cats can cause severe illness in FeLV-infected cats. These secondary infections are responsible for many of the diseases associated with FeLV.
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The only sure way to protect cats from FeLV is to prevent their exposure to FeLV-infected cats. Keeping cats indoors, away from potentially infected cats is recommended. If outdoor access is allowed, provide supervision or place cats in a secure enclosure to prevent wandering and fighting. All cats should be tested for FeLV prior to introducing them into a home, and infection-free cats should be housed separately from infected cats. Food and water bowls and litter boxes should not be shared between FeLV-infected cats and non-infected cats. Unfortunately, many FeLV-infected cats are not diagnosed until after they have lived with other cats. In such cases, all other cats in the household should be tested for FeLV. Ideally, infected and non-infected cats should then be separated to eliminate the potential for FeLV transmission.
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A relatively effective vaccine against FeLV is available, although it will not protect 100% of cats vaccinated, and it is not considered a core vaccine. Owners contemplating FeLV vaccination for their uninfected cats should consider the cats' risk of exposure to FeLV-infected cats and discuss the advantages and disadvantages of vaccination with a veterinarian. Since not all vaccinated cats will be protected by vaccination, preventing exposure remains important even for vaccinated pets.