NATURALLY-OCCURRING PERSISTENT AND ASYMPTOMATIC INFECTION OF THE GUTTURAL POUCHES OF HORSES WITH STREPTOCOCCUS-EQUI

During an outbreak of strangles on a farm with approximately 1500 hors es, the spread of Streptococcus equi infection was monitored by repeat ed nasopharyngeal swabbing and culture. To order to control the infect ion and prevent new introductions of strangles on to the premises, a s ystem of quarantine and swabbing of cases and all incoming animals was instituted, Long-term carriage of the organism was detected in four c linically healthy convalescent animals, and in two of 350 new ponies; it persisted for between seven and 39 months, but it was detected only intermittently by the culture of swabs which was a much less sensitiv e method than the culture of guttural pouch lavages taken by endoscopy (45 per cent v 88 per cent sensitivity, respectively, for any single sample), Repeated swabs were often negative for several weeks between positive samples, Nonetheless, in all but one of the long-term carrier s, S equi was detected by culture of repeated swabs taken over a perio d of less than two to three months. Infection was detected unilaterall y in the guttural pouches of five of the carriers and was accompanied by large numbers of neutrophils in the lavage samples whether or not t here was empyema Abnormalities of the affected guttural pouches were d etectable by radiography but only after the instillation of contrast m edium. The study indicated that clinically healthy long-term carriers of S equi present a serious risk of spreading strangles, particularly because they may be detected only by repeated nasopharyngeal swabbing over two to three months.