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Veterinary Forum January 2007 (Vol 24, No 1)

Clinical Report: "Tailoring vaccine protocols to each patient"

by Sophia Yin, DVM, MS (Animal Science)

    Editor's Note: With this issue, Dr. Sophia Yin begins a monthly column that will provide a brief synopsis of the latest thinking about a clinical topic. This month, she tells you how to implement a vaccine program that matches each patient's risk for disease. Next month, look for an update on pain management. — Marie Rosenthal, MS, Executive Editor

    For decades, pets have benefited from vaccines, but in recent years, vaccines have been increasingly implicated in adverse events. "In 1985, two adjuvanted vaccines — one for rabies and one for FeLV — were introduced on the US market, and, shortly thereafter, veterinarians began to recognize fibrosarcomas in cats," says Richard B. Ford, DVM, MS, DACVIM, DACVPM, professor of medicine at the North Carolina State University College of Veterinary Medicine. These observations raised concerns that led researchers to search for and finally find answers.

    "A number of studies have demonstrated an association between vaccines and fibrosarcoma, particularly with regard to these two adjuvanted vaccines," Ford adds. In addition, anaphylactic reactions are known to occur in some dogs, and immune-mediated disease has been reported anecdotally. However, because there is no national vaccine adverse event reporting agency for pets, the process of validating anecdotes is slow.

    Despite recent findings, vaccines are remarkably safe and effective, Ford says. "We use them in virtually every patient in practice today, and we are administering so many more vaccines now than we did 10 or 15 years ago." Indeed, without vaccines, we would witness the devastating effects associated with infectious disease outbreaks that developing nations encounter. For instance, 60,000 people worldwide annually die from rabies, and domesticated dogs are the principal vector. But in the United States, because dogs and cats are routinely vaccinated, only a handful of human cases occur each year, and rarely are dogs the vector, according to the Centers for Disease Control and Prevention.

    Using vaccines safely

    Given their benefits and risks, how can we use vaccines safely? The American Association of Feline Practitioners (AAFP) recently published vaccine guidelines for cats recommend that veterinarians avoid the use of vaccines that are known to be associated with inflammation (i.e., those that contain adjuvant).

    "For every adjuvanted feline vaccine today, there is a nonadjuvanted alternative with the exception of the FIV vaccine," Ford offers, "so veterinarians have a choice." In addition, vaccines that provide long-lasting immunity, such as against feline parvovirus (panleukopenia), herpesvirus, and calicivirus, can be administered every 3 years to adult cats instead of each year.

    Pets should receive only those vaccines for which they are reasonably likely to encounter disease. Thus in cats, the core vaccinations include panleukopenia, herpesvirus-1, calicivirus, and rabies. It is recommended that all kittens receive FeLV vaccine because they are at greatest risk. After 1 year of age, the AAFP guidelines suggest FeLV vaccination primarily in cats that spend time outdoors or live with FeLV-positive cats. In dogs, the core vaccines include distemper, hepatitis, parvovirus, and rabies.

    Understanding the product

    Ford stresses that, with the present-day complexities of vaccination, it is also important for veterinarians to understand what product they are using. Currently, in addition to the traditional killed and modified-live virus vaccines, two types of recombinant vaccines are available for use in companion animals: a subunit vaccine for canine Lyme disease and virus-vectored vaccines for canine distemper, feline rabies, and FeLV.

    For the subunit vaccine, recombinant refers to how the product is manufactured: The gene encoding the outer-surface protein A (OspA) from Borrelia burgdorferi is isolated and placed into Escherichia coli DNA plasmid. Subsequently, pure OspA is expressed. Thus, the Lyme disease vaccine contains only the key protein and no Borrelia organism.

    Virus-vectored vaccines are somewhat different. Here, the genes that express the immunoprotective proteins are separated from the pathogenic virus and subsequently are recombined with the DNA of a virus vector, such as the canarypox virus. The canarypox virus vector transports the selected genes into the patient at the time of vaccination. Antigen-presenting cells (APC) then capture the vaccine virus and rapidly present immunoprotective proteins to the lymphocytes. Because the canarypox virus does not replicate in mammalian cells, antibody against the vector virus is not produced.

    Studies conducted at the University of Wisconsin have demonstrated that the recombinant canine distemper vaccine is capable of immunizing puppies (based on challenge studies) despite the presence of maternal antibody. This is a unique advantage when trying to protect puppies in a high-risk environment.

    Obviously, not all vaccines are the same. The decision to use, or not to use, a particular product should be based on the science behind each vaccine—not just price or marketing. By understanding the principles behind vaccination, the type of products available, and individual patient needs, veterinarians can tailor vaccination protocols to every patient and minimize the risk for adverse effects while providing protection against devastating infectious diseases.

    For more information on the guidelines from the AAFP and from the American Animal Hospital Association or for answers to your frequently asked questions, go to Dr. Ford's vaccination website www.dvmvac.com.

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