SUSCEPTIBILITY OF PONIES TO INFECTION WITH STREPTOCOCCUS-PNEUMONIAE (CAPSULAR TYPE-3)

Welsh Mountain ponies were inoculated with an isolate of Streptococcus pneumoniae, SPE 1618 (capsular type 3) recovered from the equine resp iratory tract: 10 ml of a suspension of 10(8) or 10(9) cfu/ml were ins tilled intratracheally. Fever was observed after either dose but the g reater concentration also produced coughing, ocular and nasal discharg e, depression and enlargement of submandibular lymph nodes. Cytologica l evidence of infection was also observed in tracheal washings during the first week after inoculation and corresponded with pneumoniae from the washes. Morbid anatomical and histopathological examinations of s elected animals revealed focal pneumonia affecting the ventral lung, e specially the cardiac area and accessory lobe, with a propensity to af fect the right lung. S. pneumoniae was isolated directly in pure cultu re from these lesions or was demonstrable by immunostaining of macroph ages bearing specific capsular type 3 antigen. By 10 days after inocul ation, the ponies were healthy and had developed antibodies to S. pneu moniae. S. pneumoniae was therefore a primary pathogen in the horse un der the conditions of the challenge.