The prevalence of <i>Streptococcus equi</i> subsp. <i>equi</i> carriers in the Netherlands

BACKGROUND: Streptococcus equi subspecies equi (S. equi) carriers are thought to be important drivers for strangles outbreaks. Limited data are available on the prevalence of carriers in European horse husbandry settings. OBJECTIVES: To estimate the prevalence of S. equi carriers among apparently healthy adult horses and ponies in the Netherlands. STUDY DESIGN: Cross-sectional survey. METHODS: The carrier prevalence in the Netherlands was estimated, detecting carriers by PCR analysis of three repeated nasopharyngeal lavages at weekly intervals. Bayesian methods were used for a true prevalence estimation. RESULTS: One hundred and sixty-six horses on 86 premises were sampled. The posterior distribution gave a mean and median estimate for true prevalence of 2.0% and 1.6%, respectively, with a 95% credible interval of [0.1%, 5.9%]. MAIN LIMITATIONS: The target of 200 participants in the cross-sectional survey was not reached. The sensitivity of three repeated nasopharyngeal lavages for the detection of carriership remains uncertain. CONCLUSIONS: The carrier prevalence estimate of 2.0% reported here is in the same order of magnitude as recent reports from other countries.