The Issues Surrounding PCVAD Tissue Homogenate: What are the facts?

April 4, 2007 — AASV Staff

The AASV Board of Directors has asked that we re-run this article in light of the ongoing significance of PCVAD in many US swine herds and the continued shortage of licensed vaccine. This article first appeared in the February 14th edition of e-Letter.

The Situation: As we are all aware, morbidity and mortality associated with Porcine Circovirus Associated Disease (PCVAD) has increased significantly over the last 18 - 24 months, first in Canada and more recently in the U.S. A number of commercial vaccines have been developed worldwide. However, due to the shortage of supply, some veterinarians and producers have turned to stimulating the pig's immune system by exposing the pig to a formalin-treated tissue extract derived from infected pigs.

The AASV has received a number of questions from its membership regarding scientific, legal, liability and ethical issues associated with this procedure. In response to these concerns, the AASV Executive Committee has compiled the following set of facts in order to inform the membership about this important issue:

The Science: There have been no scientific studies to assess the efficacy of this approach and anecdotal reports indicate a varied response. Also, exposure of animals to a product of unknown purity and safety is concerning as well. The concerns regarding this process are associated with the possible lack of consistency with the manufacturing procedures (safety and efficacy), distribution of the product, and consumer acceptance.

The Legalities: AASV has discussed these concerns with representatives of the USDA's Center for Veterinary Biologics (CVB) and interpreted the following information from their comments. Issues regarding manufacture, distribution and use of veterinary biologics are addressed in the Virus-Serum-Toxin Act. Veterinarians have long enjoyed the privilege of being able to provide these types of products to our clients when complying with the guidelines set forth by the veterinary exemption as defined in 9 CFR 107.1.

This exemption has specific limitations, however. For instance, the product must be prepared by the veterinarian within the context of a valid veterinarian-client-patient relationship. Groups of farms or third-party manufacturers working for a farm or group of farms are not eligible for exemption from the regulations. This implies that products manufactured under this exemption can only be used on the farm of origin. In addition, this regulation specifically excludes from exemption "the shipment or delivery for shipment anywhere in or from the United States of any exempted product which is worthless, contaminated, dangerous, or harmful."

Without a positive demonstration that a vaccine is pure, safe, potent, and effective, the CVB would consider such product to be worthless, contaminated, dangerous, or harmful. In the case of a PCVAD tissue homogenate prepared as described above, CVB has concerns that the PCV2 virus, or other harmful organisms, may not be wholly inactivated by the use of formalin and that excessive use of formalin may denature the antigenic proteins associated with the virus, thus rendering the product contaminated and worthless. Since it is not certain that formalin fixation inactivates all organisms from the affected tissues, interstate transport of the product is illegal unless granted a permit from APHIS. The CVB has published a draft guidance document addressing the issue of circovirus inactivation on its website.

The Risk: In manufacturing, distributing and administering this product, the veterinarian assumes significant liability for its safety and efficacy. Representatives of the AVMA's Professional Liability Insurance Trust (PLIT) provided the following statement regarding malpractice coverage:

"A veterinarian should clearly understand the federal and state regulations regarding manufacturing, distributing and administering a PCVAD Tissue Homogenate vaccine before engaging in this activity, to determine if it is legal."

"The AVMA PLIT-sponsored veterinary malpractice policy, underwritten by Zurich Insurance Company, responds to covered allegations of negligence arising from a veterinary incident as defined in the policy. When a malpractice claim is presented to Zurich, the circumstances surrounding the specific veterinary incident are investigated, to determine if the coverage applies. All claims are reviewed in relation to the policy wording and are subject to policy terms, conditions, and exclusion. Malpractice claims arising from illegal activity are specifically excluded under the policy. Zurich Insurance Company makes the sole and final determination of whether coverage is applicable."

The Ethics: Veterinarians are challenged with minimizing animals' pain and suffering while being bound by the legal and regulatory constraints associated with the manufacture, distribution and use of non-licensed biologicals. Ethical consideration must also be given to the establishment of the veterinarian-client-patient relationship, unrestricted sales of product, and the distribution of product beyond the farm of origin. Ultimately, each veterinarian must utilize the best available information and science to make their individual decision on how to manage the challenges of PCVAD.

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AASV staff contributed to or researched this story. For more information about the AASV, please visit http://www.aasv.org/.