Streptococcus virus threatens Canadian swine

By Jessica Colby

Editor’s note: Jessica Colby is a University of Regina journalism student. She previously worked at the University of Saskatchewan’s Western College of Veterinary Medicine (WCVM). This article is printed with permission from WCVM Today.

University of Saskatchewan scientists are working to discover how to prevent Streptococcus equi subsp. zooepidemicus from establishing itself in swine barns.

Several years ago, no-one in the Canadian pork industry would have been concerned about the potential risk of Streptococcus equi subsp. Zooepidemicus – bacteria that can cause infection in virtually every species, explained Matheus Costa, a swine medicine specialist at the University of Saskatchewan’s Western College of Veterinary Medicine (WCVM).

“Before 2019, if anyone investigating clinical cases found this bacteria in a pig, they would suggest this is just part of its normal biota,” said Costa. “We find it in healthy pigs all the time, so we never worried about it.”

However, that perception shifted in 2019 when S. zooepidemicus began posing a serious health threat to hog herds across Canada and around the world. During that same year, researchers were alerted to S. zooepidemicus outbreaks among pigs in New Zealand and the Netherlands.

“The problem is that it looks like it flares up over and over again,” said Costa. “It just doesn’t go away. Antibiotics will suppress it, but if we take antibiotics out, it comes back again.”

As with other illnesses, some pigs can also carry S. zooepidemicus without displaying clinical signs – a finding that was recently reported by Costa and his research team.

The WCVM research group is now aiming to discover how Canadian hog farmers can prevent this disease from establishing itself in their barns. Costa is also investigating the development of non-antibiotic therapies and prevention strategies to reduce the disease’s severity. 

“Because it’s bacteria, antibiotics are usually the first thing we do. We can suppress disease by treating pigs aggressively,” said Costa.

However, veterinarians need to ensure that they are using the right antibiotic drugs to combat the infection, so they do not induce antimicrobial resistance. Costa said the main challenge is that researchers and veterinarians do not understand enough about the disease, “so we don’t know how to control it beyond antibiotics.”

Costa’s team is trying to determine what will slow the spread of S. zooepidemicus in barns, whether that includes workers washing their boots, testing every animal or depopulating a barn – a drastic option that is costly in terms of time and money.

“Depopulation means all the pigs go through the barn flow, then we empty the barn physically. Pigs are removed, and the entire barn is disinfected. Then we start repopulating,” said Costa. “We’ve done that before, and it doesn’t get rid of the bug, likely because of carrier pigs.”

As with any virus response, judicious use of antimicrobials is important. S. zooepidemicus presents clinical signs indistinguishable from African Swine Fever (ASF), making testing critical to being able to tell the difference.

Another problem with S. zooepidemicus is that its clinical signs are similar to the dangerous and extremely infectious African Swine Fever (ASF) virus that causes high mortality rates. Due to the similarities in presentation, it is impossible to distinguish between S. zooepidemicus and ASF without extensive testing.

S. zooepidemicus looking like ASF adds another layer of complexity to this, because we’re not just dealing with a new disease,” said Costa. “We need to make sure we don’t have ASF as well, so we’re both trying to rule it out from clinical cases and making sure we understand this new disease.”

S. zooepidemicus usually affects older pigs, and its initial clinical signs include a lack of appetite and lethargy.

“There is an invasion of the whole body – it goes everywhere. Once it has access to the blood, it can essentially attack any organ, and that’s what we see: septicemia,” said Costa. “We see lesions in multiple organs, and that’s where it becomes challenging to differentiate it from ASF, because that’s what the ASF virus does.”

Unless the pigs have what Costa calls “nose-to-nose contact,” there is little chance the disease will be transmitted between the animals. A recent WCVM trial concluded that the bacteria spreads through physical contact.

“We’ve learned that if we have sentinel pigs in the room together with pigs that have S. zooepidemicus, the sentinel pigs never become infected if they don’t have nose-to-nose contact,” said Costa. “They could be close – at one-and-a-half metres apart – but they don’t get it. We’re going to facilitate dealing with the disease as we progress and learn more about it.”

Saskatchewan’s Agriculture Development Fund, Alberta’s Results Driven Agriculture Research (RDAR) and Canada’s Natural Sciences and Engineering Research Council (NSERC) provided funding for this study.