Pet Articles

Cat Leukemia – Feline Leukemia

Feline Leukemia (FeLV) is similar to Feline Immunodeficiency Virus (FIV) in that it is caused by a retrovirus, is transmissible between cats, and results in suppression of the immune system. The end stage of both diseases is death from secondary infection or cancer. Just like FIV, the Feline Leukemia virus has a worldwide distribution and its prevalence in the population varies between geographic regions (please see the article entitled FIV- Feline Immunodeficiency Virus for a thorough description of the disease).

FeLV is spread very easily between cats because it is shed continuously in the saliva. An infected cat that plays or grooms with other cats will pass on the virus. Drinking from the same water bowl is enough to spread the virus through an entire household or cattery. An infected mother can pass on the virus to her kittens through the placenta but it is more likely that she will do so when she grooms them after birth. Like FIV, FeLV is NOT transmissible to humans but has very serious consequences for infected cats.

Infection with FeLV suppresses the cat’s immune system and renders it extremely susceptible to a wide range of diseases and cancer, such as upper respiratory tract infection, stomatitis (inflammation of the inside of the mouth), feline infectious peritonitis, and feline panleukopenia (‘distemper’). Upon initial infection, cats may show signs of fever, tiredness, and poor to no appetite. At this stage of infection some cats are able to mount an immune response against the virus and clear it from the body. Sometimes, the cat’s immune system is able to control the infection but not totally eliminate it, making them carriers of the disease. These cats will often show signs of FeLV infection when they are stressed or ill. Cats that are unable to eliminate the virus become persistently viremic. As the virus replicates and infection progresses, cats become repeatedly infected with other diseases that have varying symptoms. Infected cats often lose weight and become anemic, which contributes to them feeling and acting tired the majority of the time.

Just like with FIV, FeLV infection can be detected by your veterinarian with a simple blood test. The ELISA Snap test used to detect FeLV is different however than the test for FIV because it looks for the presence of viral antigen in the blood rather than antibodies. An antigen is a piece of the invading virus that the body recognizes as foreign and which stimulates the body’s immune response. Antibodies are what are made by the body’s immune system when it fights the infection. Antibodies are used to recognize and neutralize specific viruses and bacteria and they hang around long after the infection is cleared to patrol the body and look for signs of re-infection. Antibodies are the reason why the body can fight off an infection much faster the second time it is infected and the principal behind why we vaccinate against certain diseases. Since the FeLV ELISA Snap test looks for the presence of antigens it only tests positive when the cat is in fact infected with the virus. This is not affected by the vaccination status of the cat which is why it is safe and highly recommended to vaccinate cats for FeLV. Furthermore, the vaccine for FeLV uses a different antigen than the one that is screened for by the ELISA test, making a false positive highly unlikely. The ELISA Snap test for FIV, on the other hand, detects the presence of antibodies for FIV in the blood. Therefore, a cat vaccinated for FIV or a truly infected cat will both test positive for FIV. This is why vaccinating for FIV is still very controversial. Remember that no test is 100% accurate and that a positive blood test should be verified with a second method of detection.

There is no cure for a cat with FeLV. Treatment of the secondary infection and keeping the cat comfortable is the only therapy that can be done at the present time. Infected cats may have many good years of life before they become so ill that euthanasia may need to be considered. Some cats that are FeLV positive have been known to reach their full life expectancy. An infected cat in a multi-cat household will need to be isolated and all feed and water dishes kept separate. An infected cat should never go outdoors because it can pass on the virus to other cats and become exposed to other contagious diseases.

The rate of FeLV infection has dropped dramatically since we have started screening and vaccinating for it vigorously. With responsible pet ownership perhaps we can eliminate it all together. Talk to your veterinarian about how you can protect your cats from Feline Leukemia virus.

By Melanie Youngs – Pets.ca writer

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