How do I diagnose and manage a strangles outbreak in a horse herd?

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Strangles outbreak management requires simultaneous triage of clinical cases, identification of carriers, and strict biosecurity — all three tracks running in parallel from day one. --- Confirm the diagnosis first. Streptococcus equi subspecies equi (S. equi) causes strangles, presenting classically with pyrexia, mucopurulent nasal discharge, and abscess formation in the lymph nodes of the head and neck.1 Not all infected horses develop pyrexia or other clinical signs, so clinical presentation alone will undercount cases.4 Culture of nasal swabs, nasal washes, or pus aspirated from abscesses remains the gold standard for detection.12 Quantitative PCR (qPCR) is approximately 3 times more sensitive than culture and is the predominant diagnostic method in practice — in UK surveillance data, 59.6% of confirmed diagnoses were made by qPCR alone and 35.8% by qPCR combined with culture.911 qPCR targets include the SeM fibrinogen-binding protein gene, seeI, eqbE, and combinations thereof; a validated triplex assay detects eqbE and SEQ2190 with an internal extraction control to reduce false negatives.9 Serology using an inhibition ELISA (iELISA) targeting SeM antibodies can confirm herd-wide exposure in clinically normal horses and is recommended to identify animals that warrant targeted qPCR follow-up.7 All horses suspected of strangles should be initially screened with a complete blood count and fibrinogen concentration.4 Once strangles is confirmed on the farm, every horse requires upper airway endoscopy, guttural pouch lavage, and qPCR of lavage fluid to identify carrier animals.4 Carriers harbor S. equi in the guttural pouches without clinical signs and are the primary driver of persistent and recurrent outbreaks.1014 In one large Standardbred farm outbreak, 16 asymptomatic horses were PCR-positive and 48 clinically normal horses were seropositive, confirming silent spread well beyond the 62 clinical cases.3 Two horses with persistent guttural pouch infection were endos