Naturally occurring persistent and asymptomatic infection of the guttural pouches of horses with Streptococcus equi.

The research article investigates the prolonged presence of Streptococcus equi bacteria in horses which can lead to strangles, a contagious disease amongst horses, even when they appear clinically healthy.

Introduction and Objectives

• The aim of the study was to monitor and control the spread of Streptococcus equi infection in horses during an outbreak of strangles on a farm with about 1500 horses. The researchers wanted to discern the role of seemingly healthy horses, which might in fact be long-term carriers of the bacterium, in transmitting the disease.

Methods

• The researchers employed nasopharyngeal swabbing and culture methods for monitoring the spread of infection.
• To prevent the introduction of new cases, a system of quarantine was instituted for all the previously affected and newly incoming animals.
• The detection of the bacterium involved the culture of guttural pouch lavages taken by endoscopy and was compared with the culture of swabs.
• Radiography was implemented, post the instillation of a contrast medium, to identify abnormalities of the guttural pouches affected.

Findings

• The researchers detected long-term carriage of the bacterium in four clinically healthy animals and in two of the 350 new ponies, with the bacteria persisting for between seven and 39 months.
• The culture of guttural pouch lavages was found to be a more sensitive method of detection compared to swab cultures. In other words, the bacteria were detected more frequently (88% sensitivity) using this method than with swabs (45% sensitivity).
• Repeated swabs were often found to be negative for several weeks between positive samples, making detection through this method intermittent.
• The infection was found to be unilateral in the guttural pouches of five carriers and was associated with large numbers of neutrophils.
• Abnormalities of the guttural pouches infected could only be detected via radiography after the instillation of a contrast medium.

Conclusion

• The study concluded that horses appearing healthy clinically could still be long-term carriers of Streptococcus equi and pose a serious risk of spreading strangles.
• Such carriers could only be detected by repetitive nasopharyngeal swabbing over a period of two to three months.