Prior to 2019, Streptococcus equi subspecies zooepidemicus was only considered an important pathogen in Asia, with 300,000 pigs dying in a 1974 outbreak. In March 2019, North America had its first case in swine production with a high mortality outbreak in Canada. The first U.S. cases with significant mortalities were then reported in Ohio and Tennessee with subsequent identification in Pennsylvania and Indiana.

Since then, no cases of Strep zoo have been confirmed in the U.S. swine herd; however, that has not been the case for our neighbors to the north.

“The big point to make is that it mimics reportable disease, so that's African swine fever. In Canada and North America, we’ve undergone extensive training and exposure to recognition of ASF. And so, this was a moment in practice,” said Frank Marshall, a veterinarian with Marshall Swine and Poultry, based out of Camrose, Alberta. “Over 40 years, we've watched so many emergent pathogens over the years from ‘mystery swine disease’ as it was called, PRRS in the early or late 1980s, to circovirus.”

Marshall presented a clinical picture of how the pathogen has impacted sow herds he works with during a recent Swine Health Information Center/American Association of Swine Veterinarians webinar.

Over one weekend, the 5,600 sow, three-site system had more than 60 deaths, which Marshall said was above normal as the farm has about a 12% annualized mortality on sows. Clinical signs showed sows off feed, severely depressed, recumbent and lethargic. Staff described them as being “pancaked.” Rectal temperatures were incredibly hot, and staff were quite alarmed by the severe reddened sclera and conjunctiva, and even bleeding from the eyes.

Twelve hours from the onset of going off feed, with or without aborting, the sows would die, thumping respiration terminally.

“So, they’re dealing with advanced pulmonary edema,” Marshall said. “Initially, the carcasses are pale, some with only slight discoloration of ears, as you'd expect with septicemia. If they lived long enough, you could get all the classic blue blotchy body and ears and such.”

At that point, they’d only had three early farrowings with piglets that were all dead. The manager had started treating the sows on the Saturday and Sunday prior.

The sow site has gilt grow out within one of the barns, and they receive 230 gilts per month at 35 kilograms. The last group had entered one week prior. Two new workers had started seven to 10 days prior, and one of them was working in the area, the night of infection.

Water is supplied from a dug-out source, so the farm is using some chlorine and there are algae evident on the dugout. Migrant waterfowl are also present, and the farm is in the middle of H5N1 avian influenza outbreaks that have been occurring.

The feed mill is offsite and services seven other feeder sites and nurseries. The last feed delivered to the sow barn was three days prior.

“Throughout this time, we had a history of corn use and diets that had resulted in gastric ulcers and GIT upsets, due to out of feed events, bridging and potentially mycotoxins,” Marshall said. “At this time in September, the first killing frosts are driving mice into the barns.”

Postmortems on arrival found pronounced pulmonary edema with interlobular edema and froth filled airways, right-sided heart enlargement with decompensation, and dramatic splenomegaly. All stomachs were half full of feed, with no evidence of esophageal ulceration. Kidneys and liver were normal; however, gallbladder walls were severely edematous and thickened. Every lymph node in the body was congested and hemorrhagic.

On the site, there are two 2,800 sow barns side by side. Each one was built 10 years before the other. The initial affected area was in the breeding and gestation barns through the common hallway, where staff walk between all the barns.

“I've got girls that are standing right beside ones that are treated that are still eating and on feed. That was kind of bizarre, in that they share a trough, 40 sows share one trough,” Marshall said. “And so, I could have sows dying right beside ones that are absolutely normal and never blink.”

While Western Canada has the “luxury of being high health,” and free of porcine reproductive and respiratory syndrome and mycoplasma for the most part, Streptococcus suis is still a major pathogen of concern. At first, their working diagnosis was septicemia. The pathologist report came back with very severe septicemia and DIC, the disseminated intravascular coagulation, and strep zoo as the No. 1 culture.

In this instance, Marshall said gestation crates really helped to pick out these animals that were off feed and sick. One of the areas Matheus Costa, lead researcher and assistant professor at the University of Saskatchewan, found was that nose to nose was essential for transmission, as the virus doesn’t “aerosol.”  

With water troughs common between 40 sows, saliva and stable foam should have been transmitting. In feces, the virus dries off quickly and is overgrown by the microbiome. Under perfect lab conditions, the bug can only survive 12 days or less. Incubation could be as long as one to seven days. All the autogenous vaccines failed across multiple systems, and during a live variant trial, Costa was able to show the vaccine was fully protective without harm on the challenge model.

“We're learning through Matheus’ work. He had demonstrated that when pigs are colonized, 90% will remain positive with strep zoo and mandibular lymph nodes and associated lymph nodes of the area,” Marshall said. “So, we went on to try and monitor in the nursery and grow-finish to establish whether or not we had good colonization. We were assuming it acted like strep seus, mom colonizes the kids, and they grow out on the finish floor in our nursery. We actually enjoyed like 2% mortality throughout this timeframe, and on the finished floor, nothing blinked.”

Going forward, the farm decided to treat the virus as zoonotic, with staff potentially being exposed every day. To handle deads or treat sick pigs, staff were expected to wear protective eyewear, N95 masks, disposable nitrile gloves, etc. Showering in and out, wearing clean barn clothing each day, and reminding staff not to take their phones in the barn became essential.

In late January, a second wave of sow mortality hit again. A shortage of Tilmiscosin in Western Canada delayed feed medication and lengthened the second outbreak extensively, Marshall said.

“In this episode, 400 sows died or were euthanized; our first wave, we lost 300. So, at this point, gilts now are starting to become affected as they move from the gilt grow out into the breeding barn,” Marshall said. “In total, we lost 750 sows, they had died or were euthanized. In Canada, when we look at the value of a sow, mid parity or pregnant, the loss of her would be basically $1,750. So quick math we were looking at a $1.3 million loss plus all our treatment costs.”

In July, the finished floors started breaking. They also started seeing plant condemnations and group closeouts that were hit, doubling the mortality, and approaching 8% to 9% in some groups.

Marshall said there are many questions surround Strep zoo that still need to be answered such as:

In 2019, the first Canadian outbreak hit a 3 by 3,000 electronic feeding system free-stall sow farm, which had an additional 10% or more mortality.

“I think we had an advantage in that our sows were still in gestation crates,” Marshall said. “In that system, the cumulative death loss of those three sow herds was over 1,000 animals in a 12-week period. Our abortion rate during that time was 11 times normal.”