Streptococcus equi subsp. zooepidemicus septicemia: First confirmed case in Ontario swine

Josepha DeLay, Đurđa Slavić, Hugh Cai, Jim Fairles, Ryan Tenbergen

Animal Health Laboratory, University of Guelph, Guelph, ON (DeLay, Slavić, Cai, Fairles); Demeter Veterinary Services (Tenbergen)

AHL Newsletter 2021;25(1):11.

A diagnostic workup was carried out in a swine herd to investigate sow anorexia, unexpected deaths (5 times normal rate), and an increase in the rate of abortions / pregnancy loss (range of 2-4 times normal over 15 weeks).  Postmortem examination of 1 dead sow identified fibrinous peritonitis and congested, edematous lungs.  Histological lesions included: pulmonary microvascular thrombosis with alveolar edema and fibrin exudation; fibrinosuppurative perisplenitis (peritonitis); and splenic congestion with intralesional bacterial cocci.  The histologic findings supported septicemia as the cause of the sow’s death.  Streptococcus equi subsp. zooepidemicus was isolated by bacterial culture in low to moderate numbers from each of spleen, lung, and kidney.  PRRSV was not detected in lung by PCR.  Surveillance PCR testing for African swine fever was carried out through the CanSpot ASF project, and the result was negative.  Abortion cases were not investigated, but were presumed to be the result of maternal illness.

Recent literature reports have described S. zooepidemicus septicemia as the cause of unexpected deaths and abortions in sow herds in Manitoba, and in mature animals and feeder pigs at an assembly yard and an abattoir in the US (1,2).  In the US cases, mortality was significant at 30-50% over a period of 8-10 days (2).

Postmortem lesions reported are those of septicemia and are not specific to this organism, but may include:

  • mild mucopurulent rhinitis
  • pulmonary edema
  • hemorrhagic lymphadenopathy (particularly submandibular, cervical, and bronchial nodes)
  • splenomegaly (mild to moderate)
  • gall bladder edema
  • fibrinous epicarditis
  • fibrinous perisplenitis
  • multiorgan congestion

Isolation of the organism from filtering organs (spleen, lung, kidney) is required for diagnosis. 

Advanced sequencing techniques have identified a common strain of S. zooepidemicus isolated from the reported cases that is thought to be more virulent than typical commensal strains found in pigs and other species.  For the S. zooepidemicus isolate from the Ontario case, whole genome sequencing (WGS) and multilocus sequence typing (MLST) at the Animal Health Laboratory identified a sequence type (ST194) similar to isolates from the recent Manitoba and US outbreaks. 

S. zooepidemicus is a potential zoonotic pathogen, similar to S. suis.  Zoonotic transmission has not been reported from any of the recent North American outbreaks.   AHL

1. Costa MO and Lage B. Streptococcus equi subspecies zooepidemicus and sudden deaths in swine, Canada.  Emerging Infectious Diseases 2020;26(10):2522-2524.
2. Sitthicharoenchai P et al. 2020. Cases of high mortality in cull sows and feeder pigs associated with Streptococcus equi subsp. zooepidemicus septicemia.  J Vet Diagn Invest 2020;32(4):565-571.