Today's Veterinary Practice

MAY-JUN 2013

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEwEd VITAL VACCINATION SERIES Antibody TiTers versus VaccinaTion Richard B. Ford, DVM, MS, Diplomate ACVIM & ACVPM (Hon) T he publication of vaccination guidelines for dogs and cats (see Links to Vaccination Guidelines, page 38)—intended to provide useful insights on the selection and use of vaccines—also elicited some degree of controversy regarding implementation of these vaccination recommendations in practice. DURATION OF IMMUNITY CONCERNS In particular, the recommendation to administer core vaccines to adult dogs and cats at 3-year intervals (or longer) rather than annually resulted in differences of opinion among veterinarians. After all, veterinarians have been recommending annual boosters for years, doing so in accordance with manufacturer recommendations. Therefore, the growing group of veterinarians who were skeptical of triennial vaccination recommendations began measuring antibody titers from individual patients to assess duration of immunity (DOI) and determine whether a patient required revaccination. As demand for vaccine titers increased, veterinary laboratories began offering antibody titer panels for dogs and cats while 2 companies developed in-clinic antibody tests. With the increased focus on antibody titers, additional questions were raised: • What are the indications for performing titers? • When interpreting antibody titers, what test limitations apply? • How should test results be interpreted when making vaccination decisions for individual patients? CORRELATION OF TITERS & IMMUNITY Antibody titers measured in laboratories and by in-clinic and antibody test kits typically record results as positive or negative, and include a brief description of the result's significance. However, questions remain: • How well does a positive antibody titer (or test kit result) correlate with protective immunity in a patient? • How well does a negative titer (or test kit result) correlate with susceptibility in a patient? When interpreting antibody titers, a few facts must be clear: 1. The only true test of protective immunity involves exposure (challenge) to a virulent pathogen in which nonvaccinates (controls) are infected and manifest clinical illness while vaccinated animals remain healthy. Animal vaccines are licensed based on this premise. 2. Interpreting antibody test results depends on understanding what results do and do not represent. In the clinical setting, antibody levels offer diverse and distinct clinical applications (see It's All About PIE, page 36). 3. Different classes of antibody, also called immunoglobulin (Ig), have specialized functions (identified and categorized as IgA, IgG, IgE, or IgM). In veterinary medicine, the antibody titers used to assess protective immunity typically represent the IgG class. 4. When using an in-clinic test kit to measure (qualitative or semiquantitative) antibody levels, results are reported as either positive (indicates protection) or negative (indicates susceptibility) and must be correlated with gold standard laboratory tests, such as virus neutralization (VN) or hemagglutination inhibition (HI), in order May/June 2013 Today's Veterinary Practice 35

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