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Issue 2 Feline Leukemia Prevention and Vaccination Feline Leukemia (Felv) infection may cause several disease syndromes involving the blood (hemolymphatic) and immune defense systems of the body. (See Issue 1) Recurrent exposure results in a permanent infection rate of about 30%. Felv infected cats may be asymptomatic for many years. Endemic infection in not uncommon in groups of stray and feral cats. The best prevention is to limit exposure. Indoor only house cats are obviously at very low risk compared to the indoor/outdoor pet or total outdoor semi wild cat. Feline leukemia virus testing must be recommended for all cats. This insures that the virus is not inadvertently introduced into the household via the newly acquired pet or that cats with latent virus but without any signs of disease (asymptomatic Felv positive virus producers) do not put other cats at risk. Positive cats shed large numbers of viral particles in their saliva and disseminate the disease by licking and grooming for the most part. The test itself is really quite straightforward. Virus protein is identified in the blood by one of two methods. The routine (ELISA) test requires only a drop of blood or in some cases, tears or even saliva. ELISA stands for enzyme linked immuno absorbent assay. Antibodies to the virus protein are used to produce quick testing that is often done in house by your veterinarian using commercially available test kits. The test is reliable and specific for the presence of circulating virus protein. Alternatively, virus protein may be identified in circulating blood cells themselves by the IFA (indirect fluorescent antibody test) which is considered to be even more specific for active infection, ie 99% versus 95% for the ELISA test. This test requires blood samples to be sent to laboratories for analysis. Generally, testing is first done by the ELISA method due to cost and convenience. In the case of questionable results the IFA test is recommended to confirm persistent infection. Testing is recommended at twelve weeks but earlier testing may be done to confirm a negative status. Positive tests in asymptomatic younger kittens may not imply persistent infection since exposure may result in only transient infection due to the cats immune defense response in many cases. Vaccination is recommended in those cats at higher risk for exposure, ie the indoor/outdoor cat, or those cats that are unfortunately routinely exposed to other cats that are known to be infected in the household. Vaccination is done as early as twelve weeks of age and repeated one month later with a booster vaccination. Currently, yearly booster vaccination is recommended. Commercially available vaccines include several types based on either whole killed virus, sub-unit particle (virus protein components), and recombinant (genetically engineered) virus protein stimulation of the cats immune response. There is some concern that vaccination may be associated with the development of tumors at the site of injection. Approximately 1-3 patients per every 10,000 vaccinated cats may be at risk. It is difficult know if yearly vaccination increases this risk but there is enough concern that some institutions are currently giving booster vaccination at three year intervals and a recent symposium on vaccination procedures has considered this as an option. The problem for your veterinarian is that not all vaccines appear to be equal in stimulating immunity and protection. Several studies have demonstrated varying levels of protective antibodies and immunity using various available vaccines. At best the rate of protection may approach approximately 80% in patients with the potential for repeated exposure. Current AVMA recommendations are for yearly vaccination in cats at higher risk, although studies are being encouraged and a task force has been formed to investigate the true risk of tumor development. ods. The routine (ELISA) test requires only a drop of blood or in some cases, tears or even saliva. |