From veterinarian to forensic detective: Solving a mysterious swine disease

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In fall 2019, a client called into Four Star Veterinary Service clinic in Mexico, Indiana, and reported the loss of a lot of sows. Daniel Gascho, DVM, knew the client and headed out to the business site, which was a buying station.

On the way there, Gascho said he had several ideas of what could cause the sow mortalities before arriving. But once he was on site, he knew he was wrong.

“It’s really a good reminder that no matter how many times you think you know all the diseases…Then you get there and it wakes you up and reminds you, ‘Oh, there’s stuff out there you’ve never seen before,’” Gascho said.

Heavy death loss

The first clue of an unusual situation was the high number of mortalities. Gascho estimated a capacity of about 1,000 hogs at the site. About 500 head died in a week.

“If that many pigs are dying that fast, I initially wasn’t thinking a pathogen…because in this country we don’t have many diseases that kill pigs that fast, that many,” Gascho explained.

Then he explored the possibility of other “one-off stuff that they mention in vet school that you almost never actually see.” One was a lightning strike but that didn’t make sense. The other was a toxin in the water or feed.

“But the odd thing was, at the same buying station were multiple species. They were not affected. If it was something in the water, it’s pig specific.”

Next, he checked out the feed for the possibility of botulism, excess ionophores or anything else. But he learned the company bringing in the feed takes the exact same diet to other finishers in the area, and no other site was affected. He also looked at other environmental issues like stray voltage, ventilation failure or pit gases. These were dead ends too.

Forensic investigation

“I felt like a forensic investigator,” Gascho said. “I’m taking feed samples and water samples, checking other species, checking the environment and just really scratching my brain.”

During the first visit to the site, Gascho did report the situation to the authorities in case it turned out to be a foreign animal disease. He also took a full set of samples for testing at Iowa State University’s (ISU) diagnostic lab.

“Of course, they tested for everything under the sun,” he said. “Negative, negative, negative.”

Smoking gun

Gascho was called out to the buying station again. This time, the client had brought in 500 to 600 feeder pigs for a roaster market. The pigs were in perfect health, but half of the pigs died within 48 hours of arrival.

“It was still a disaster at this point,” he said. “I’m standing in a pen…and pigs were literally dying in front of me.”

Gascho again collected sets of tissues from multiple pigs as well as samples of feed, water, etc. He sent everything off to the ISU lab for more testing.

Eventually, the lab noticed an unusual pattern with a pathogen that normally causes disease in horses and not swine. But in every sample cultured from the sick pigs, the same pathogen showed up.

S. zooepidemicus

The mystery was soon solved. Repeated lab tests showed the pigs were dying from Streptococcus equi ssp. zooepidemicus. It was the first diagnosis of the disease in swine in the US.

“It’s just an extremely acute, full-bodied systemic bacterial sepsis, raging inflammation of every organ, organ failure and death,” Gascho explained.

There was a silver lining to the diagnosis. “It was susceptible to about every readily available product we have,” he added. And the pathogen also did not appear to aerosolize.

Gascho and the client were able to depopulate pens, clean and disinfect them, and successfully move new pigs in without any further problems.

Mystery solved.

 

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.