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Diagnosing Viral Myelitis Cases In Pigs – Priority And Practice

On December 4, the Swine Health Information Center (SHIC) and American Association of Swine Veterinarians (AASV) sponsored a webinar titled, “Disease Management of Viral Myelitis.” Designed for veterinary practitioners and pork producers, information presented by diagnosticians as well as case studies provided insight into symptoms of these central nervous system (CNS) diseases, appropriate steps for diagnosis, as well as on-farm management experience with porcine astrovirus 3 (PoAstV3), porcine sapelovirus (PSV), and porcine teschovirus (PTV). A video of the webinar presentations is available here.
Dr. Matthew Sturos, University of Minnesota Department of Veterinary Population Medicine, noted symptoms of CNS disease include incoordination/ataxia, weakness, head tilt, inappropriate mentation, circling, blindness, knuckling, tremors, paddling, paresis, and convulsions. Each of these symptoms has a root cause from differing segments of the CNS: brain, vestibular, or cervical.
An appropriate diagnosis is important because other causes of similar symptoms can be the result of non-spinal diseases. Diagnostic assays for viral myelitides require fresh tissues for testing and analysis. During the webinar, Dr. Sturos detailed the appropriate sampling options for accurate diagnoses. In addition to the processes for sample collection, he also said it will help the pathologist when information included with the submission includes the CNS signs. He also recommends submission of non-CNS tissues for the best testing protocol and results.
Dr. Bailey Arruda, Iowa State University Veterinary Diagnostic Lab, further emphasized the necessity of aseptic collection. She also described the necessity of choosing the right pigs for tissue collection, noting disease progression will impact the accuracy of analysis.
With PSV and PTV, Dr. Arruda noted affected herds have pigs from 4 to 16 weeks old impacted with a case fatality rate of 90% to 100%. The typical disease duration is less than four days in individual pigs, weeks to months in a group of pigs, and months to years in intergroup settings. PoAstV3 has been diagnosed around the world with five lineages identified. Pigs from 20 days of age through sows are impacted when infection is present. There is a case fatality rate of 90% to 100%. Treatment has been unrewarding.
Dr. Arruda said fecal shedding of all three viruses is common. She also said development of CNS disease is relatively uncommon, pointing to risk factors for infection of co-infections, genetics, immune response, and maternal immunity as well as diet and microbiota.
In addition to the technical information provided by Drs. Sturos and Arruda, three swine practitioners shared their experience with CNS diseases. Dr. Grant Allison, Walcott (Iowa) Veterinary Clinic, described a client’s PoAstV3 infection. Dr. Pete Thomas, Iowa Select Farms, explained how they managed a PTV diagnosis. And Dr. Aaron Lower, Carthage (Illinois) Veterinary Service, detailed their client’s PSV experience. These case studies illuminated the realities on the farm including diagnosis, recovery, treatments, and learning.
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