Streptococcus equi subsp. zooepidemicus update

Đurđa Slavić, Murray Hazlett, Jim Fairles         Animal Health Laboratory, University of Guelph, ON

AHL Newsletter 2020;24(1):9.

Streptococcus equi subsp. zooepidemicus is a Gram-positive commensal bacterium frequently present on mucosal surfaces. Although primarily considered an equine pathogen, S. zooepidemicus can cause infections in a variety of animal species, including humans. Most recently, S. zooepidemicus was reported as causing abortions, conception failures, and sudden death in gilts and mature sows in Manitoba on four epidemiologically-linked premises. Following this initial report, sudden death of pigs caused by S. zooepidemicus at two different Manitoba assembly yards and at slaughterhouses in Canada and the USA was observed. These cases were also epidemiologically linked to the index premises.  Streptococcus zooepidemicus was consistently isolated from all cases and isolates were submitted for whole genome sequencing (WGS). WGS revealed that these isolates are closely related to the S. zooepidemicus ATCC 35246 strain that caused significant losses in the swine industry in China in 1976. 

A search of the AHL database since May 2007 revealed isolation of S. zooepidemicus from various animal species.  As expected, this bacterium was predominantly cultured from equine samples followed by bovine, feline, canine, small ruminants and porcine. Occasionally, it was also isolated from alpacas, camels, llamas, grey squirrels, ferrets, chinchillas, deer, and birds. A closer examination of porcine cases (12 in total including 4 research cases) revealed that S. zooepidemicus had been isolated only once (2011) in pure culture from a joint sample. In all other cases, S. zooepidemicus was isolated in mixed culture in combination with Streptococcus suisStaphylococcus aureusBordetella bronchiseptica, or Trueperella pyogenes. In 4 research cases, S. zooepidemicus was isolated from tonsils of healthy pigs collected at slaughterhouses, confirming that this organism can be part of the normal mucosal flora in healthy pigs. 
AHL continues to monitor all porcine cases for the presence of S. zooepidemicus. Recovered isolates will be stored for future testing, including WGS of pathogenic strains, if required.  AHL


1. Feng Z, Hu J. Outbreak of swine streptococcosis in Sichuan province and identification of pathogen. Anim Husbandry Vet Med Lett 1977;2:7-12.

2. Costa MO, Lage B. Streptococcus equi subsp. zooepidemicus associated with sudden death of swine in North America.  bioRxiv. 2019; doi: