Does the FeLV Vaccine Cause Cats to Become Positive on the SNAP FeLV ELISA Test?

That leukemia vaccine was a snap.
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Before you have Fluffy vaccinated for feline leukemia, your vet will blood test him to make sure he hasn't already been exposed to the virus. If your cat has been vaccinated previously, that won't cause him to turn up as positive on this test. That's not true of another vaccine.

Feline Leukemia

The very contagious feline leukemia virus (FeLV) generally spreads via contact with saliva. That means a cat can pick it up not only if bitten during a fight, but from food and water dishes used by infected felines. The immune system of some cats can eliminate the virus and become immune. Those cats aren't the majority, however, numbering about 40 percent, according to Greenbrier Veterinary Hospital. Symptoms of FeLV infection include fever, weight loss, dental and gum disease, diarrhea and upper respiratory infections. Affected cats also might suffer cancer or diseases because of compromised immune systems. There is no cure for feline leukemia, which eventually proves fatal. However, some cats that test positive might not come down with symptoms for many years. Good supportive care can help extend their lives.


Although the feline leukemia vaccine isn't considered one of the core vaccinations by major professional veterinary organizations, your vet might recommend this shot for your cat. That's true especially if Fluffy goes outside or comes into contact with strange felines. The initial two shots are given at two- to four-week intervals, with a yearly booster after that. Because the FeLV vaccine can cause a rare cancer, known as a fibrosarcoma, at the injection site, your vet will give your cat an inoculation in the left hind leg. If Fluffy does suffer a tumor at the site, leg amputation can save his life.


The Enzyme Linked Immunosorbant Assay test, better known as the ELISA, checks for evidence of the FeLV virus in feline bodily fluids, including saliva or blood. It's also called a SNAP test because of its brand name. Your vet conducts this test in her office, so she knows whether your cat has an early stage infection or one in the later stage. If it's an early stage, she'll perform the test again in about a month's time to see if the cat or kitten has fought off the infection. There is no point in vaccinating an infected cat against FeLV.

Feline Immunodeficency Virus

Symptoms of the feline immunodeficiency virus (FIV) often mimic that of FeLV. FIV is similar to the Human Immunodeficiency VIrus (HIV) responsible for AIDS in people. Although a vaccination is available for FIV, it will render an FIV-negative cat positive for a SNAP ELISA test for at least a year after the inoculation, according to the University of California at Davis School of Veterinary Medicine. In addition, it might not protect a cat against all strains of FIV. Always consult an experienced veterinarian regarding the health and treatment of your pet.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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