Two factors underlie strangles importance as a disease. Firstly, around 10% of cases develop more severe
clinical signs which occasionally prove fatal. Secondly S. equi has evolved to persist in the equine population.
After normal infection, a proportion of cases, known as carriers, remain persistently but asymptomatically
infected. Carriers appear outwardly normal but infection usually persists in the guttural pouches; in-contact
horses can become infected through intermittent shedding of S. equi. Together with the unrecognised and thus
untreated atypical cases, carriers are likely to contribute significantly to the disease persistence. Identification
of both carriers and atypical cases is difficult by conventional means.