There’s No Playbook for Astrovirus Type 3, Sundberg Says
Porcine astrovirus type 3 (PoAstV3) has been causing central nervous system (CNS) disease for at least a decade. Experts agree that it’s difficult to diagnose and manage. Unfortunately, there’s not a playbook for this devastating virus yet.
“Astrovirus is one of a complex of viruses that can cause what’s termed myelitis, an inflammation of the nervous system, especially in the central nervous system,” explains Paul Sundberg, executive director of the Swine Health Information Center (SHIC). “With astrovirus, the pigs knuckle, they go down, they are alert, but they may not be able to move. They may be uncoordinated and can seem to be in paralysis.”
Although the diagnostic labs don’t see that many cases of PoAstV3, Sundberg says it’s a virus SHIC is keeping an eye on for several reasons.
“There’s no vaccine. It can be diagnosed and the diagnostic labs do find it intermittently,” he says. “But there really isn't what I term a ‘playbook’ for it – here’s what you should do.”
In a recent webinar sponsored by SHIC and the American Association of Swine Veterinarians, experts who have had experience with PoAstV3 came together to discuss what they’ve learned – sometimes the hard way – from this troubling virus.
“Our goal is to learn from other’s experience,” Sundberg adds. “If pigs get this on the farm, it's got a 100% fatality rate, and you can lose up to 10% of your pigs. That's a real issue. What we're trying to do is give people information about how others have handled it, what they can expect to see, what they can do for diagnostics, and then how perhaps they can manage it on their farms.”
PoAstV3 on the Farm
In the webinar, Kayla Henness, DVM and herd veterinarian with The Maschhoffs, and Todd Williams, DVM and head of contract research at Pipestone Veterinary Services, shared their experiences with PoAstV3 on the farm.
Henness discovered PoAstV3 on a 5,000-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 veterinary diagnostic lab (VDL) with no significant findings reported, she explained. When fixed and fresh cerebrum were submitted, however, PoAstV3 was diagnosed.
To combat the virus, Henness initiated a controlled exposure event with the goal of uniform exposure and immunity across the farm. She said they used a protocol similar to a porcine epidemic diarrhea virus (PEDV) process. Based on results from testing, she 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.
The Maschhoffs are working with a third-party lab on an experimental PoAstV3 vaccine using spinal cord sequenced from the affected farm, she said. They also made extra exposure material as a backup to be used in the event of a flare-up before the vaccine is ready.
Williams found PoAstV3 in a 3,000-sow farrow-to-wean facility in southeast Iowa with a traditionally high health flow. In this situation, a sow was good one day and bad the next, he said, reluctant or unable to get up. The following day, the sow would not rise or 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, he said. 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. Williams said he also saw positive response to whole herd feedback, as well as in the gilt development unit feedback program at 18 weeks of age.
Veterinary Diagnostic Labs Weigh In
Fabio Vannucci, DVM of the University of Minnesota, and Bailey Arruda, DVM of Iowa State University, shared tips on collecting the right tissues for submission and disease trends at VDLs.
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 emphasized being specific about the CNS signs to aid in diagnosis.
Viral poliomyelitis appears similar regardless of cause, 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.
At the Iowa State University VDL, Arruda usually sees a handful of cases each month being tested for PoAstV3. She 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, she explained, 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, she noted.
Reviewing submission data from the Iowa State VDL, 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.
The experts agreed that learning continues, and unanswered questions remain. SHIC is monitoring the number of CNS cases that are happening in its swine disease monitoring report that comes out each month.
“We want to keep an eye on this to see if Astrovirus might be something that emerges more in the future. We're trying to monitor this and make sure that if it's going to happen more widely, one, we're going to find it early, and two, we've got some information that might help people manage it,” Sundberg says.
Watch the webinar here.
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