Deadly swine-disease outbreak at buying station triggers search for mystery pathogen

When a call came into the office last September reporting very high, unexplained sow mortalities, Daniel Gascho, DVM, didn’t expect it to be anything unusual. But when the veterinarian with Four Star Veterinary Service in Mexico, Indiana, went to investigate, he found quite the opposite.

The site was a Midwest buying station with cull sows and boars collected for market. At first, just a few sows died, and alarms weren’t raised. Cull markets and buying stations are inherently at a higher risk for diseases, Gascho said.

But then 1,000 roaster pigs were unloaded at the station and they started dying, raising serious alarms.

“We had high-health, 50-pound pigs coming onto the site with no clinical signs of disease, and within 48 to 72 hours, half of them had died,” Gascho said. “It was worse than anything I’ve ever seen for an infectious disease, considering how fast they were affected after exposure. At this point we were ruling out toxin, ventilation failure or something along those lines. If infectious, it almost had to be something we were not familiar with in this country.”

Getting a diagnosis

Gascho reported the event to the proper authorities and sent off tissue samples to Iowa State University Diagnostic Laboratory for a diagnostic work-up. Worried it could be a foreign animal disease, he was relieved to have African swine fever (AFS) and similar diseases ruled out right away.

While they waited for a positive diagnosis, the buying station implemented biosecurity and depopulating protocols for the facility.

But it took a week to receive a diagnosis. “Unfortunately, most of the rapid tests we have available are for specific pathogens, so there were a lot of negatives before something was found,” Gascho explained.

The culprit: S. zooepidemicus

After ruling out many different things, the test results came back suggesting the mortality could be due to bacterial sepsis caused by Streptococcus equi ssp. zooepidemicus (S. zooepidemicus). This was the first diagnosis of S. zooepidemicus-associated mortality in pigs in the US.

Fortunately, S. zooepidemicus is typically highly treatable and susceptible to many readily available medications. But at buying stations, pigs are heading directly to market and cannot be medicated just before slaughter, in order to meet withdrawal requirements. This created perfect conditions for the bacteria to flare up at the site.

The buying station started what is known as a “rolling depopulation” as soon as ASF and other foreign animal diseases were ruled out. Once they knew the culprit was S. zooepidemicus, they moved ahead with a rolling depopulation that included emptying pens, setting biosecurity lines and disinfecting pens before new animals moved in.

“The disease appears to spread very rapidly by direct animal contact and through fomites and the environment, but poorly by aerosolization or through the air,” Gascho said. “We never had that barn completely empty but maintained a buffer zone of several disinfected empty pens between pens that had not yet been emptied and cleaned and the recently disinfected pens. The disease did not spread. We depopulated pen by pen until all pens were emptied and cleaned.”

Disease spread

How did this disease get into the US? One possible route is from Canada. The pathogen was found in cull sows in western Canada during May 2019. A year earlier, an outbreak of S. zooepidemicus occurred in mares, also in western Canada. The disease is most commonly found in horses; however, it can be transmitted to other animals and humans, but rarely.

“The natural suspicion is that this highly pathogenic form of the bacteria came into [the US] by Canada because a lot of their cull sows are brought here,” Gascho said.

After the disease hit the buying station, other episodes of excess cull sow and finisher mortalities occurred at slaughter facilities in Wisconsin, North Carolina, Florida and other states. Authorities believe the episodes were epidemiologically linked and are unlikely to represent new outbreaks. By late October, mortality rates at these facilities had returned to normal.

Wake-up call

Even though S. zooepidemicus is now in the US, Gascho doesn’t believe it poses a major problem for our swine industry.

“It’s very treatable, but you need to catch it fast,” he added. “If it’s a weekend and someone’s not around to check a nursery or finisher as often as they should, within a few hours a lot of damage can occur quickly.”

The S. zooepidemicus outbreak is a peek at what could happen with a major foreign animal-disease outbreak.

“It raised awareness to our shortcomings on our ability to control disease and how the steps we have in place to prevent these situations don’t always go as planned,” Gascho said. “I sent in the information and it took a week to get a diagnosis, simply because we’re limited to looking for what we know is out there. New things result in new challenges.

“It’s a good wake-up call if we were to get a foreign animal disease in this country,” he concluded.

 

Three-step approach for spotting sick sows

A three-pronged approach to observing sows can help identify illness, lower mortality and increase productivity, according to a leading vet.

Bill Minton of Four Star Veterinary Service, Chickasaw, Ohio, said taking a closer look at pigs during farrowing, gestation and lameness can reveal potential problems before they become serious, Pork Network reports.

And by training staff to look and respond to signs of sickness quickly, producers can improve animal well-being and their bottom line in one move.

Farrowing watchfulness

Farm staff should regularly check to see how the gilt or sow adjusts to being in a farrowing crate and whether she is eating and drinking, cleaning the feeder, or is in distress, Minton advised.

Most operations have someone in the room during the farrowing process, checking the sow regularly. If too much time passes between pigs being born (more than 20 or 30 minutes), someone should manually check the sow.

Post-farrowing care

Make sure all the afterbirth has passed and that the sow is well and eating normally — especially during lactation, Minton emphasized.

Check that sows are comfortable and monitor their body condition, especially at warmer times of the year, he added.

“At some farms we take a rectal temperature routinely at 24 hours post-farrowing to make sure we don’t have residual complications and that she’s properly cleaned. Uterine infections will show up on temperatures of 103 degrees or more,” he explained.

If a sow has a high temperature, it will be put off from eating and drinking, which will affect milk production.

Lactation care

During weaning, make sure the udder is functioning properly and do everything possible to enhance appetite for increased milk production, Minton said.

Gradually reduce room temperature to keep sows comfortable, and address signs of shoulder sores and lesions as they appear.

Prevention is the key to minimizing the number of sick sows during farrowing and lactation, he said, which means early detection is critical.

Gestation observation

Minton said that a thorough, daily observation during feeding will have the biggest impact on evaluating sows. Farm staff should listen for abnormal sounds like coughing and panting, and look for abnormal stools and signs of lameness, he added.

“Record and follow-up on suspect sows,” he says. “Make a note and call it to someone’s attention or take proper action.”

Eliminate lameness

More than 50% of sow deaths are caused by lameness, but early intervention and aggressive treatment could reduce that figure significantly, Minton said.

“If you have a 2,500-sow operation and you’re not treating 8 to 10 sows on a daily basis, you’re probably not treating enough,” he said.

Lameness can be caused by housing, diseases, injury, nutrition, environmental issues or genetics.

“Look for sows that have difficulty standing or rising,” Minton advised. “If animals shift their weight or tap their feet, look for swelling, cuts or bleeding. If an animal avoids the group or is walking slowly, check them out more closely.”

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