Correlation between endoscopic findings and real-time PCR analysis for Streptococcus equi subsp. equi DNA of guttural pouches in recovered strangles cases

Abstract

Horses that lack obvious clinical signs of respiratory disease can be silent carries of Streptococcus equi subsp. equi (S. equi) in their guttural pouches. Guttural pouch lavage and repeated nasopharyngeal lavages(1) analyzed by real-time PCR(2) are sensitive methods for analysis for S.equi and are considered to be a standard to identify carrier stage. The carrier screening, identifying and treatment of carriers, in the end of a disease outbreak by sampling guttural pouches is expensive and time consuming. According guidelines carriers that have endoscopic findings of guttural pouch empyema, chondroids or discharging lymph nodules are sampled and treated. The sensitivity of using macroscopic appearance of guttural pouches as an indication of persistent S. equi colonization is poorly studied. The aim of this study was to investigate if there is a correlation between endoscopic findings in guttural pouches and positive qPCR analysis for S.equi. In total 179 endoscopic findings from upper airways from 91 individual horses after a strangles outbreak were compared with positive qPCR results from nasopharyngeal lavage and guttural pouch lavage samples. Nasopharyngeal lavage was performed with 120 ml saline and guttural pouch lavage with 40 ml saline for each pouch and analyzed separately. The nasopharyngeal lavage was performed with 120 ml saline prior endoscopy and endoscopic guttural pouch lavages using 40 ml saline for each pouch and analyzed separately. The endoscopic findings of guttural pouches, including empyema, chondroids or discharging retropharyngeal lymph nodules were recorded and compared to the qPCR analysis for S. equi. Therewas no statistical correlation between endoscopy findings and qPCR results. However, if the first guttural pouch lavage was positive by qPCR for S. equi, it was statistically more likely that the contralateral guttural pouch also was positive, indicating a risk for contamination of the second sample. Horses that lack obvious clinical abnormalities on upper airway endoscopy including the guttural pouches can be silent carriers of S. equi. In conclusion, negative endoscopic findings of the guttural pouches of recovered strangles cases cannot rule out silent carrier status. This study was approved by the Swedish Ethical Committee on Animal Experiments and each horse owner had given their informed consent to participate in the study. Financial support was achieved from The Swedish-Norwegian Foundation for Equine Research and Swedish Research Council Formas.