E50 - Biosurveillance of Streptococcus Equi Subsp. Equi in Nasal Secretions of 9,409 Equids Across the USA

Background: Strangles has remained a very important respiratory disease in horses worldwide, with little epidemiological studies available.
Hypothesis/Objectives: The aim of the study was to describe selected epidemiological aspects of horses with acute onset of fever and respiratory signs testing qPCR-positive for Streptococcus equi subsp. equi (S. equi). 

Animals: 9,409 horses with acute onset of fever and respiratory signs from all regions of USA were included in a voluntary biosurveillance program from 2008-2020.
Methods: Information pertaining to demographics, location, season, clinical signs, and vaccination status was collected. Nasal swabs were collected and tested via qPCR for S. equi and common respiratory viruses including equine influenza virus, equine herpesvirus-1/-4, and equine rhinitis A/B virus.
Results: A total of 715 (7.6%) of study horses tested qPCR-positive for S. equi, of which, 226(32%) had coinfections. The median age for the S. equi qPCR-positive horses was 8±4 years and nasal discharge (639–89%) and fever (590–83%) were the most common clinical signsreported in these horses. There was a significantly greater number of horses testing qPCR-positive for S. equi during winter and spring compared to summer and fall (P< 0.001). Also, there was a significant difference (P = 0.001) in the frequency of reported S. equi vaccination between S. equi qPCR-positive (89 horses) and S. equi qPCR-negative cases (824 horses).
Conclusions and clinical importance: The qPCR prevalence of S. equi in the USA was 7.6%, supporting the endemic occurrence of strangles. Further, horses vaccinated against S. equi were less likely to test qPCR-positive against S. equi.