Ontario’s senecavirus outbreak in hogs differed from U.S.

Two southwestern Ontario sow barns were infected in June 2018

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Ontario’s latest cases of the obscure Senecavirus gave the hog farming sector a chance to practice managing a new disease outbreak.

Why it matters: The most significant known risk is that, based on clinical signs alone, Senecavirus is indistinguishable from foot-and-mouth disease — meaning that when it’s discovered, all pig travel must cease until the Canadian Food Inspection Agency receives confirmation it’s not foot and mouth.

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Tavistock-based veterinarian Dr. Ryan Tenbergen says he will remember it for a long time. He described his experience with the disease at the recent Shakespeare Swine Seminar.

The virus appeared in two sow barns in June 2018, the first cases traced to a farming operation. Some cull sows were found with the virus’s nose lesions in 2015, but they weren’t able to be traced back to individual farms.

Tenbergen said the outbreak was “the first case of its kind in a commercial herd in Canada.”

A relatively newly identified disease, Senecavirus was first isolated from outbreaks between 1988 and 2001 in the United States, and only given a name in 2002.

“Really, right now, not much is known about the virus,” Tenbergen said, including what actually makes the virus cause clinical disease, and what are the predisposing factors to being affected by these symptoms.

Symptoms are scours in piglets, sows off-feed and fevered, lesions on the snout, and ulcers where the hoof meets the skin. It’s usually accompanied by a minor spike in sow mortality for about three weeks. And it’s definitely seasonal. “It’s always between June and August when you see an uptick,” Tenbergen said.

In the barns he worked with, the first sign, explained to him through a memorable phone call on June 27, was sows off feed accompanied by some scouring. Later that day, he received another call reporting blisters on some snouts.

Although his initial consultation involved a single facility, once the diagnosis was made the manager of a related facility also realized the same thing was happening. It turned out the two sow barns had been affected “basically at the same time.” Tenbergen didn’t visit the sites during the outbreak, but did visit with the farmer later, during the follow-up period. At the time, photos sent to him, as well as the explanation from the barn manager, were enough for him to make the determination that the pigs should be tested for Senecavirus.

Dr. Paul Sundberg of the Iowa-based Swine Health Information Center said during a subsequent Shakespeare Swine Seminar presentation that one challenge of keeping ahead of a Senecavirus outbreak is the fact it often causes only a minor increase in sow mortality. Although the disease’s long-term effects in the form of poor-performing hogs and sows could potentially be significant, the short-term effects in the form of mortality might not always catch the attention of swine production managers.

“For a lot of these barns, unless they’ve got really good record-keeping for deaths, (an outbreak of Senecavirus can) slip under the radar,” Sundberg offered.

The disease, he explained, “blew up” in the U.S. — beyond what he described as “a few cases in show pigs and 4-H projects” — in September of 2015. Investigation revealed that, as had been the case with a previous smaller outbreak in the U.S., it followed on the heels of a similar outbreak in Brazil during the southern hemisphere’s summer in January and February of the same year. Sundberg stressed there has been no connection confirmed between either of the U.S. or Brazil outbreaks, but it is suspicious.

Sundberg added the Ontario case study differed from what has been experienced in the U.S. because it was first detected in sows while there were very few initial clinical signs among nursery pigs. So far in the U.S., outbreaks of Senecavirus have manifested themselves through extensive scouring in piglets, but only a one to two per cent spike in sow mortality.

Tenbergen noted that the strain of Senecavirus isolated from the Ontario herd was unrelated to any of the strains contained in a U.S.-based gene bank of swine diseases. Regardless, he agreed with Sundberg that it can take an astute barn manager to notice any signs.

“It can easily be missed,” said Tenbergen, who works out of Tavistock for the Quebec-based Demeter Veterinary Services. “Really, not a lot of animals are going to show these signs.”

The cases he encountered weren’t the disease’s first instance in Canada. In June 2007, market hogs from Manitoba arrived with the virus at a slaughterhouse in Minnesota. Then in the fall of 2015, cull sows from Manitoba and Ontario arrived at the U.S. border with lesions on the snout.

CFIA traced back and discovered positive animals in some assembly yards. But it could not be traced back to any particular farms.

It’s “a bit of a mystery” as to why the 2007 and 2015 pigs tested positive for Senecavirus, Tenbergen said. “I don’t know if anything was ever found.”

As for the more recent outbreak, he hopes the cause of the infection and the vector of transmission will eventually be found.

Although the CFIA “pretty much wiped their hands of it” after it was determined not to be foot-and-mouth disease, there are still a number of specialists looking into the outbreak in search of clues.

About the author

Contributor

Stew Slater operates a small dairy farm on 150 acres near St. Marys, Ont., and has been writing about rural and agricultural issues since 1999.

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