Researchers have identified a new strain of Strep zoo as the cause of sudden sow mortalities in Canada and the United States, but many questions remain unanswered.
by Jackie Clark
A pathogen that is familiar in the horse world now seems to have entered swine herds in North America, with deadly consequences. The bacterial strain is called Streptococcus equi subspecies zooepidemicus, or Strep zoo for short.
Starting in April 2019, officials reported localized outbreaks of Strep zoo as the cause of pig mortalities in Manitoba. Since the fall, officials have reported cases in some American states too, including Tennessee and Pennsylvania.
Better Pork spoke with swine industry veterinarians and a Manitoba hog farmer to learn about the nature and status of the disease. We explain what Strep zoo is and how it affects pigs. We also explore how the industry can combat the disease and what we still don’t understand about the bacteria.
What is Strep zoo?
Strep zoo bacteria can be present in many healthy animals without having negative health effects.
Streptococcus equi is “a normal inhabitant of horses. When it gets systemic in horses, it causes an infection called strangles,” says Dr. Paul Sundberg, the executive director of the Swine Health Information Center, in Ames, Iowa.
“Strangles is a reportable disease, potentially lethal to horses, and it’s been detected everywhere across the globe, including Canada,” explains Dr. Matheus Costa. He’s a resident and an adjunct professor at the University of Saskatchewan’s Western College of Veterinary Medicine.
The subspecies zooepidemicus “will colonize and infect a range of hosts,” he adds. Colonization means that the bacteria are present and can occur without illness. Infection, however, leads to disease.
“The literature has reported over 20 species being diseased from Strep zoo infection. That (list) includes birds, mammals and reptiles,” Costa says.
Until recently, scientists were not concerned about Strep zoo in swine.
“Over the last 20 or 30 years, you find sporadic references to (Strep zoo) from various lab reports and veterinary case studies on it affecting pigs, but the (reports) have always been really sporadic,” says Dr. Egan Brockhoff, the veterinary counsellor of the Canadian Pork Council (CPC).
Costa agrees. The bacterial strain “has never really been a problem for the swine industry. We know pigs are colonized, so Strep zoo is nothing but another part of the tonsil microbiota, that community of bacteria that live in the throats of pigs,” he says.
It appears that, in some herds, the situation has changed.
“Now, there seems to be something different with the Strep zoo that makes it more aggressive toward pigs,” Costa says.
Dr. Jette Christensen, the manager of the Winnipeg-based Canada West Swine Health Intelligence Network (CWSHIN), agrees. CWSHIN connects swine industry stakeholders across Western Canada who share information about swine health concerns.
“Apparently this new strain is more serious for pigs,” she says. “It’s been detected on a couple of farms in Manitoba. … It’s causing problems in sows and gilts – reproductive problems and mortality.”
Because Strep zoo is part of the normal biome, tracking where this new strain emerged from is difficult, Costa explains.
“Although Canada was the first (country) to report, there were cases of mortality in other countries,” he says. These cases include mortality events in Tennessee and Pennsylvania, according to a U.S. Department of Agriculture (USDA) emerging risk notice from November 2019 and the Pennsylvania Department of Agriculture.
Effects on pigs
Officials faced challenges when they tried to better understand how Strep zoo infections progressed in pigs because “one of the biggest clinical presentations was sudden death,” Sundberg says.
“A veterinarian reported … that you could look at a pig that was up and moving and looked normal. Thirty minutes later, it was down on its side, gasping and ready to die,” he says.
In fact, deaths were so sudden that veterinarians initially suspected poison, Sundberg says. The disease can cause death so quickly because it is septicemic, meaning the disease invades the blood stream, he explains.
The Strep zoo infection then progresses without many observable symptoms.
“Once (Strep zoo) has invaded the host and gains access to the blood stream … the pig goes into shock. Essentially, it’s a very strong response to invasion,” Costa explains.
In cases where death isn’t sudden, a range of symptoms can occur, Sundberg says.
Those symptoms include lethargy, vomiting and fever, Costa explains.
Strep zoo may also cause symptoms which present like pneumonia or lung disease, Christensen adds.
The diverse symptoms, as well as sudden deaths, make Strep zoo a difficult disease to diagnose.
“This strep infection can look like a lot of other things,” says Sundberg. “The only way to identify (the disease) as a cause of mortality (in pigs) is to culture it. There’s no way you can look at a pig, even with an autopsy, and say definitively that (the disease) is Strep zoo.”
In Canada, the infection has been associated with pigs in stressful situations.
“Once culled sows (are sent) to slaughter and the transport is long or they’re (held) for a couple of days at assembly yards … the disease seems to flare up and kill off sows,” Christensen says.
Costa agrees. Strep zoo mortalities “were associated with stressful events … usually following transportation. That’s when the sows would present with sudden death,” he says.
Movement and the mixing of pigs contributed to the spread of the disease, Brockhoff adds. “It just moved through natural pig flow,” he says.
Nose-to-nose contact of pigs could be the method of transmission.
“What we believe so far is that the main way these bacteria gain access to the pig is through the nose,” Costa says. “It’s probably being swallowed as well through nasal secretions.”
Stopping Strep zoo
There is good news. “If you can get to the pigs (in time), it is a treatable condition,” Sundberg says. “My understanding is that this isn’t bacteria that has a lot of resistance to antibiotics.”
Rapid identification will be central to combatting Strep zoo.
“Our veterinary diagnostic labs in Canada are very capable of isolating the (bacterium), growing it and identifying it,” Brockhoff says.
“Antimicrobials are an effective way to treat the disease, like all bacterial infections, once it’s taken hold. Biosecurity is still the key to prevent” infection and spread, he adds.
For farms that have had mortalities caused by Strep zoo, the controlled and restricted access zones will be a renewed focus, says Rick Bergmann, a Manitoba hog farmer and chair of the CPC.
And biosecurity isn’t restricted to individual farms. It includes acute, industry-wide emergency measures if officials detect Strep zoo.
“If there is a case of sudden death somewhere in the system, stop pig movement,” Costa says.
“As long as we identify the pathogen quickly, we can treat those animals. We can isolate them and stop this (disease) from spreading,” he adds.
Communication between relevant stakeholders is an industry strength, Bergmann says.
The CPC focuses on communication “to ensure that we can notify producers if there are potential risks that they should be aware of,” he says.
Connections between the CPC, provincial pork councils, swine veterinarian networks and pork producers help focus the entire industry on swine health.
“There’s a strong link between all of those entities. That’s what has given us really good success (in preventing disease) here in Canada to date,” Bergmann explains.
“We have that good relationship here, and we (extend) that good relationship beyond our borders” to include counterparts in the United States, he adds.
This collective responsibility prevented Strep zoo from spreading further in Canada during the 2019 outbreak, which was isolated on several farms in Manitoba.
“It’s a good news story that we were able to raise (Strep zoo) as an issue and discuss it, so it wasn’t a massive problem in Canada before anybody heard about it,” says Christensen. The limited spread of the disease is an accomplishment.
So far, the swine mortalities all seem to be related to one specific strain, but “we don’t know where it came from,” says Christensen.
The USDA has initiated research to better understand how the disease affects sows, and Iowa State University is studying the effects on younger pigs to better understand transmission and the mortality rate, Sundberg explains.
Currently, most of what we know is “based on observations from clinical outbreaks,” says Costa.
“We learned that it’s somewhat easy to stop (Strep zoo) from moving if pigs are not being mixed or moving from room to room and if proper internal biosecurity is followed,” Costa adds.
By determining where the disease came from, industry stakeholders will be able to create more effective disease-prevention strategies.
Because animal scientists are familiar with Strep bacteria in general, “I don’t expect there to be big surprises,” says Brockhoff. But “there are probably going to be some lessons learned in swine.
“Maybe the biggest (issue) would be to better understand what risk pathway allowed (the disease) to get into a barn,” he says.
The veterinarians don’t expect Strep zoo to pose a major risk to the health of humans or other animal species.
This strain “is different from Strep zoo that will infect other species,” Costa says. “There isn’t really a major zoonotic concern.”
Brockhoff agrees. It’s “not likely that this (bacterial strain) will continue to make any significant changes,” he says.
Producers should be aware – but not necessarily afraid – of Strep zoo.
“The most important thing that any famer can do is pay attention to the health of his or her pigs,” Sundberg says.
“If someone observes sudden death in sows, alert the veterinarian. Make sure he or she can collect the proper samples,” Costa adds.
Biosecurity is important “no matter the size” of the swine operation, he says.
Bergmann expands on this point. Pig farmers face “some significant risks,” even from producers who have a small “backyard or outside production,” he says.
“A $500 operation could pose a risk to a $5-million operation. So, somehow, we have to ensure that (smaller operations) will not be the weak link in the chain,” he explains.
Canadian farmers can rely on their veterinarians to learn about emerging disease risks.
“On my farm, if there are emerging diseases, we have a veterinarian whom we work with. We would expect that they would be very close to the situation,” Bergmann says.
Producers are also doing their part to ensure Strep zoo doesn’t become a bigger threat in Canadian swine herds.
“Producers in Canada spend a lot of time on biosecurity,” Bergmann says. They shower in and out of restricted and controlled access zones, change clothing and put “a tremendous amount of effort into washing and disinfecting trailers,” he explains.
That dedication has likely contributed to the containment of Strep zoo.
“I think, through diligence and good biosecurity, we’ll slow this bug down for sure,” says Brockhoff. “There doesn’t appear to be any more significant spread.”
But farmers should pay close attention to new pigs coming onto their farms, he says.
“If you’re bringing in breeding stock, it’s absolutely critical that you do a vet-to-vet (consultation). … Talk about the history of the herd,” he says.
Producers should “direct single source pigs,” he adds. “Don’t buy pigs from an assembly yard and auction barns (or through) any kind of community share program.”
A lot of unanswered questions still surround Strep zoo, Bergmann says. However, for producers, the principles of disease prevention remain the same.
“Our world is biosecurity for our animals. That’s the best focus, and that would be the best solution to keep our animals healthy,” Bergmann says. BP