Veterinary Medicine - August 2007 - (Page Insert1)

Immunology Bulletin Antibody titer testing By Richard B. Ford, DVM, MS, DACVIM, DACVPM (HON), and Alice M. Wolf, DVM, DACVIM, DABVP In response to evolving canine and feline vaccination guidelines, veterinarians have expressed concern that some patients might be susceptible to infection if vaccines are not administered annually. These concerns prompted serologic testing to ensure that triennial vaccination of adult dogs and cats would provide a level of protective immunity no less than that derived from the administration of annual boosters. Today, several laboratories offer serologic panels that include antibody titers to selected antigens, particularly the core antigens, used in companion animal vaccines. This availability of serologic assessment for individual patients prompts questions concerning when to perform the tests as well as how to interpret the results. This issue of Immunology Bulletin addresses the role of postvaccinal serology (antibody titers) in dogs and cats. What are antibody titers? Serum antibody titers represent the relative concentration of circulating antibodies, usually IgG, to a particular antigen. It’s important to note that although testing individual patients for antibody titers is becoming increasingly available, such testing does not provide a comprehensive assessment of immunity. Antibody titers represent only a portion of the overall immune response a patient can mount following exposure or infection. Most laboratories limit antibody testing to one or two classes of immunoglobulin: IgG and possibly IgM. Quantitative measures of cell-mediated immunity, although important in long-term immunity and recovery from infection, are not provided through commercial diagnostic laboratories. A few facts should be considered when using antibody titers to assess vaccine response. First, with the exception of rabies titers, standardized laboratory methods for determining serum antibody concentration for vaccine antigens have not been established in the United States. Also, methods vary among laboratories—one may use virus neutralization assays to establish a titer for canine distemper (which is recommended), another may report results using less sensitive test methods, such as immunofluorescence assays. For an individual patient, results reported by one labora- tory can differ substantially from those reported by another. Comparing test results between laboratories is not recommended. Second, while all vaccines stimulate antibody responses, all antibodies are not protective. Leptospirosis titers, for example, are routinely used to establish exposure and infection to pathogenic serovars. Vaccine-induced titers for leptospirosis, however, are short-lived and poorly correlate with protection. Third, laboratories offering vaccine antibody titers do not provide results for every vaccine antigen used. Only selected titers provide reliable information regarding protective immunity. For example, positive antibody titers to canine distemper virus (CDV), canine parvovirus (CPV), and feline parvovirus (FPV), also called panleukopenia virus, reliably reflect that a patient is capable of mounting a protective immune response if exposed. Some laboratories offer titers for other infections, such as canine adenovirus-1 (hepatitis), feline herpesvirus-1, and feline calicivirus. However, the significance of the results can be unclear. Finally, a positive antibody titer in blood collected today is not predictive of the patient’s titer tomorrow. Titers are only reflective of antibody levels on the day that serum was collected. Interpreting a positive titer to mean that the patient does not need to be vaccinated or retested for another year may be inappropriate. What are the indications for performing antibody titers? Veterinarians cite several reasons for performing antibody titers in individual patients. For example, owners who are particularly concerned about the potential for vaccine-induced injury may request titers in lieu of annual vaccination. Veterinarians who are reluctant to implement triennial vaccination recommendations for core vaccines may elect to submit serum for titers annually before administering a core vaccine. In addition, it may be helpful on occasion to know whether an individual puppy or kitten failed to respond to the initial vaccine series (i.e., maternal antibody interference). In such cases, it would be appropriate to submit serum a minimum of two weeks after administering the last vaccine in Supported by Merial www.Merial.com http://www.Merial.com

Table of Contents Feed for the Digital Edition of Veterinary Medicine - August 2007

Contents A Veterinary Medicine Interview Veterinary Voices Idea Exchange Diagnosis and Treatment of Solar Dermatitis in Dogs Diagnostic Imaging for Linear Foreign Bodies in Cats Overcoming the Diagnostic and Therapeutic Challenges of Canine Immune-Mediated Thrombocytopenia Ophthalmic drugs: What’s new? CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - August 2007

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