During a webinar sponsored by the Swine Health Information Center (SHIC) and American Association of Swine Veterinarians (AASV), practitioners and diagnosticians discussed porcine astrovirus type 3 (PoAstV3) which has been causing central nervous system (CNS) disease for at least a decade. Disease can be difficult to diagnose and manage. PoAstV3, spread by the fecal-oral route, has been associated with paresis, paralysis, knuckling, incoordination, and lateral recumbency in pigs at various production stages. Click here to access the webinar.
Dr. Kayla Henness, herd veterinarian with The Maschhoffs, and Dr. Todd Williams, head of contract research at Pipestone Veterinary Services, shared their experience with PoAstV3 on the farm. Dr. Fabio Vannucci, University of Minnesota, and Dr. Bailey Arruda, Iowa State University, shared information on collecting the right tissues for submission and disease trends at veterinary diagnostic labs (VDLs).
Dr. Henness detailed the discovery of PoAstV3 on a 5000-head sow farm where it was initially assumed to be untreated lameness. The case fatality rate was between 90% and 100% when the animal was displaying neurologic symptoms with no response to treatment. Fresh lung, liver, kidney, and spleen were submitted to a VDL with no significant findings reported. When fixed and fresh cerebrum were submitted, PoAstV3 was diagnosed.
To combat the virus, Dr. Henness initiated a controlled exposure event with the goal of uniform exposure and immunity across the farm. She stated they used a protocol similar to a porcine epidemic diarrhea virus (PEDV) process. Based on results from testing, Dr. Henness and her team created the feedback material from post-farrowing gilt manure, piglet manure from litters less than five days old, distilled water, and table salt. Testing after exposure to the feedback materials showed a decrease in infection and sow mortality dropped as well.
Dr. Henness said The Maschhoffs are working with a third party lab on an experimental PoAstV3 vaccine using spinal cord sequenced from the affected farm. They also made extra exposure material as a backup to be used in the event of a flare up before the vaccine is ready.
In Dr. Williams situation, PoAstV3 was found in a 3000 sow farrow-to-wean facility in southeast Iowa with a traditionally high health flow. In this experience, a sow was good one day and bad the next, reluctant or unable to get up. The following day, the sow would not rise nor raise its head. There was no response to antibiotics or anti-inflammatories. The sow would be off feed and slightly lame on a front limb then rapidly progress to lateral incumbency.
Diagnostics on the three sows initially exhibiting the symptoms showed all had inflammatory changes in the brain consistent with a viral cause, per results of submission to a VDL. The neurologic exam on the sow farm showed nystagmus was mostly absent, palpebral reflex was positive, deep pain present to tail, and hyperesthesia. In the neurological exam of finishing pigs, nystagmus was positive as was palpebral reflex. Again, there was deep pain present to the tail as well as ataxia, muscle tremors/weakness, and hyperesthesia. Dr. Williams reported he also saw positive response to whole herd feedback, as well as in the gilt development unit feedback program at 18 weeks of age
Dr. Fabio Vannucci shared information on sampling collection of the spinal cord for better diagnostic results, recommending a dehorner for the process. He also advised localizing CNS signs to collect the correct tissue samples for submission. To help the pathologist, he also said being specific about the CNS signs will be helpful for diagnosis.
Viral poliomyelitis appears similar regardless of cause, Dr. Fannucci cautioned, noting it will require ancillary tests for definitive diagnosis. He also suggested submitting non-CNS tissues (intestine, muscle, liver, serum) along with feed samples to ensure diagnosis.
Dr. Arruda said the Iowa State University VDL usually sees a handful a cases each month being tested for PoAstV3. She echoed the clinical signs shared during the webinar by the practitioners and pointed out that paresis of the front limbs is usually either porcine sapelovirus (PSV) or PoAstV3. She recommends aseptic collection of brainstem, spinal cord submission, and cerebrum for diagnostic accuracy. When an animal is down in back, for example, the caudal spinal cord is the appropriate sample. When down in front, the cranial spinal cord is preferred. She also says opening joints is important for best results. Picking the right pigs for the samples is essential as well, illustrating disease progression in samples will help, but not more than three pigs are needed when using a solid case definition.
Reviewing submission data from the Iowa State VDL, Dr. Arruda said cases of PoAstV3 have been diagnosed in animals from 20 days of age to sows. The case fatality rate is 90% to 100% with herd mortality from 0.1% to 10%. In a pig, PoAstV3 has a duration of less than four days. Within a group, it lasts weeks to months. Intergroup duration can extend to years. She also said treatment is generally unrewarding.
Dr. Arruda and colleagues have conducted field trials to further learn how to manage PoAstV3, details of which were shared during the webinar. Learning continues and unanswered questions remain. She said infection and fecal shedding are common, however, development of CNS disease is relatively uncommon.
SHIC/AASV sponsored webinars bring together subject matter experts to discuss current issues facing US pork producers and practitioners. Past topics have included viral myelitis, tracheitis, coccidiosis, and lameness/arthritis. Conducted by the Iowa State University Swine Medicine Education Center (SMEC), webinar participants include practitioners with first-hand experience with the topic being discussed, diagnosticians, and other experts. Completed webinars are posted online for convenient access here.
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