Dutch study estimates silent strangles carrier prevalence at 2%

A Dutch cross-sectional survey published in Equine Veterinary Journal estimates that 2.0% of apparently healthy adult horses and ponies in the Netherlands are silent carriers of Streptococcus equi subsp. equi, the bacterium that causes strangles. The study, led by researchers from Utrecht University and Royal GD, tested 166 horses across 86 premises using PCR on three repeated nasopharyngeal lavages taken at weekly intervals. The authors reported a mean true-prevalence estimate of 2.0%, with a 95% credible interval of 0.1% to 5.9%, and said the finding is broadly in line with recent reports from other countries. They also noted two important limitations: the study fell short of its 200-horse enrollment target, and the sensitivity of repeated nasopharyngeal lavage for detecting carriership is still uncertain. (research-portal.uu.nl)

Why it matters: For equine veterinarians, the headline isn't that carriers are common, but that a small, clinically silent reservoir appears to persist even in a general, outwardly healthy population. That matters because silent carriers are widely considered a key source of new strangles outbreaks, and current guidance still points to repeated nasopharyngeal lavage or direct guttural pouch sampling as the main ways to identify them. Other published work has shown that long-term carriers may be missed depending on sampling site, and UK surveillance has previously found that a substantial share of positive laboratory diagnoses came from outwardly healthy carrier horses. In practice, the Dutch data reinforce the value of outbreak follow-up, screening protocols before movement or mixing, and careful interpretation of a negative result when clinical suspicion remains. (research-portal.uu.nl)

What to watch: The next question is whether follow-on studies using guttural pouch sampling, larger cohorts, or risk-factor analysis narrow that estimate and better define which apparently healthy horses are most likely to be true carriers. (research-portal.uu.nl)