Scratchings-and-Sniffings

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Vaccine Associated Sarcomas in Cats Posted: 21 May 2009 12:23 PM PDT We've touched on this issue before in general discussions on feline vaccination protocol. There is no doubt that VAS is a significant issue in veterinary medicine and one reason the vaccine protocols have undergone scrutiny and revision over the years. The adoption of core versus non-core vaccines is in part due to the risk of VAS. There is a statistical link between vaccination with certain types of Feline Leukemia and Rabies vaccination and the occurrence vaccine associated sarcoma. The estimated risk for developing VAS is between one and ten cats for every 10,000 cats vaccinated.   Although that makes this a fairly rare problem the sarcoma itself is a very serious issue for any cat that develops one. These sarcomas are very malignant and reach deep into surrounding tissues making them very difficult to treat once they are diagnosed.   In the past, the use of vaccinations that use certain types of adjuvants resulted in a higher level of vaccine site reactions. Adjuvants are commonly used to enhance the ability of a vaccine to stimulate immunity. Vaccine site inflammatory reactions are thought to be a possible precursor to VAS development and some studies have shown that one in 35 to 40 reportable vaccine reactions will progress to tumor formation. There may also be a genetic component that leads to VAS in certain cats, too.   Recent developments in vaccine technology may help reduce the risk. There are newer vaccines available that do not rely on adjuvants and produce far fewer local injection site reactions. The American Association of Feline Practitioners recommends the use of vaccines that are less inflammatory. You still have to weight the risk of vaccination against the risk of developing the actual disease. The incidence of Feline Leukemia has decreased by 50% over the last twenty years, but it is still the leading fatal infectious disease of adult cats. The main reasons for the declining incidence of FeLV are testing and vaccination.   Cats that are at high risk are those cats that are likely to come into close contact with infected cats. Infected cats can live for months to years after infection and be capable of spreading the virus. If you allow your cat to roam freely, he is at risk. If you have multiple cats with unknown infectious status, any cat you introduce will be at risk. If you have cats living with a known infected cat, these cats are at risk, and finally, kittens are at greater risk than adult cats, particularly kittens born to infected mothers.   The following guidelines should be followed to reduce the incidence and risk of developing Feline Leukemia (FeLV).  Indoor cats are at low risk and do not need to be vaccinated. Another great reason to keep you cat indoors.  New cats in multiple cat households should be tested negative for feline leukemia before they are introduced into the household.  Testing is recommended before vaccination and only FeLV negative cats should be vaccinated.  Vaccinating FeLV positive cats has no benefit in altering the course of the disease.  The risk of vaccination in adult cats at low risk may be higher than the risk of infection.  Cats at high risk should be vaccinated annually until they are no longer in the high risk category. The American Association of Feline Practitioners recommends the use of the newer less inflammatory vaccines discussed above.  Hopefully, by following these guidelines we can continue to reduce the risk that any cat will develop Feline Leukemia or develop Vaccine Associated Sarcoma.

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