Tim Pasma, Patricia Bell-Rogers

Animal Health Laboratory, University of Guelph, Guelph, ON.

AHL Newsletter 2025;29(4):27.

The AHL has had a qPCR for the diagnosis of strangles caused by Streptococcus equi subspecies equi (Streptococcus equi) in place for over a decade. The PCR test is highly sensitive but cannot differentiate between live or dead bacteria. The alternate test, bacterial culture, has a lower sensitivity and a longer turnaround time.

Occasionally, positive PCR tests may occur in horses without clinical signs or with a negative bacterial culture. This can occur if the horse was exposed to or is carrying a low level of bacteria, is in an early stage of infection or has clinical signs that were missed in the early stage of infection or was previously vaccinated. Contamination of equipment or samples may also cause a false positive PCR test.

Testing for S. equi can be optimized by:

• taking samples for PCR (sensitivity) and culture (viability)
• testing at weekly intervals if an infection is suspected
• sampling both the nasopharynx and guttural pouch by lavage
• ensuring that the endoscope and other equipment is thoroughly cleaned and disinfected between uses.

If you obtain results that are not expected based on clinical findings and history, please contact AHL to review the result and possible options.

The AHL strives to provide same-day S. equi testing for samples received before 11AM. Our quality program is at the core of what we do, and occasionally a test will fail its quality control check and may need to be repeated the next day. Please indicate on the submission form if you would like rush testing or if you are requesting same day results so that the lab is aware of your needs