Clinical Signs and Shedding in Strep Zoo Challenged Pigs By Ed Metzger from South West Ontario Veterinary Services

Streptococcus equi subspecies zooepidemicus (Strep zoo) is usually identified as a commensal bacterium of horses. Strep zoo was first reported as a severe clinical disease in swine in Canada in 2019. At that time it was associated with sudden deaths, increased abortion rates and septicaemia in sows. The initial case resulted in up to 40% sow and gilt mortality in Manitoba herds as well as in sows in lairage in a sow processing plant in Tennessee. At that time S. zooepidemicus sequence type 194 was associated with these severe losses. In December 2020, the first case of Strep. zoo in swine in Ontario was isolated at the Animal Health Laboratory, University of Guelph. The Ontario case was associated with septicemia and elevated mortality in sows. Strep zoo continues to be present in Ontario and Strep zoo has also caused an outbreak of mortality in finishing pigs in Ontario.

Unfortunately, there is little data available regarding this disease in pigs. These Canadian researchers wanted to investigate the clinical progression, pathogen shedding, transmission as well as the gross

visible and microscopic lesions following infection in pigs. Six-week old pigs were inoculated with either S. zooepidemicus sequence type 194 (inoculated, n = 6) or sham inoculated with sterile culture broth (sentinels, n = 4). Animals were housed in the same room, in two pens that were 2 meters apart. Pigs were monitored twice daily for clinical signs. Rectal, nasal and oral swabs were collected once daily to see if the S. zoo could be detected. A full necropsy was performed if welfare was a concern, or at 5 days post-inoculation (dpi).

The researchers found the following:

  • All sentinels that were housed only 2 meters away from affected pigs remained disease free and their samples tested negative for the Strep zoo pathogen.
  • All challenged inoculated pigs developed fever within 8 hours of inoculation and they went on to develop severe disease after 2 dpi.
  • A total of 4/6 inoculated pigs developed severe clinical signs that compromised animal welfare and these pigs were euthanized before 5 dpi.
  • Strep zoo was found in nasal swabs (15/23) and rectal swabs (9/23) in affected pigs.
  • Clinically healthy, inoculated pigs had detectable levels of S. zooepidemicus in rectal and nasal swabs.
  • All 6 inoculated pigs whether clinical or subclinical had post mortem evidence of reactive submandibular lymph nodes, kidney bleeding spots and enlarged spleens. (These types of post mortem lesions could look like the lesions of African Swine Fever (ASF) and as such would be eligible for CANSpot ASF confirmatory negative testing)

Take Home Message

  • It appears that direct animal to animal contact is the most likely method of transmission but more studies should be carried out to confirm this.
  • It appears that subclinically infected pigs may be able to spread the disease through nasal secretions and feces.

Submitted by Ed Metzger, DVM

Ref: Matheus de Oliveir a Costa, J ohn Clar e Samuel Har ding, Yanyun Huang, Roman Nosach. Str eptococcus equi subsp. zooepidemicus infection of pigs leads to shedding in feces and a carrier state. Transbound Emerg Dis. 2022 Feb 19. doi: 10.1111/ tbed.14481. Online ahead of print.