Equine strangles modelled in mice

Small animal models of Streptococcus equi infection have been confined to parenteral injection of mice which subsequently develop a septicaemia. To devise a model of infection more closely resembling strangles, 4.9 x 10(6) cfu of S. equi were placed on the nares of C3H and Balb/c mice (fifteen of each). Compared with ten uninfected controls, infected mice sneezed more often and their daily weight gain was significantly reduced. Histopathological examination seven days after infection revealed varying degrees of nasopharyngeal and regional lymphoid pathology in twenty two mice. Eleven mice had an early or mild rhinitis in which the nasal epithelium presented microabscesses containing polymorphonuclear leucocytes. Another eleven mice had a suppurative rhinitis or pharyngitis associated in most with regional lymphadenitis; in two mice, abscessated lymph nodes had erupted into perinodal connective tissues. Two mice had a vestibular abscess. The suppurative rhinitis was associated with extensive necrosis of nasal propria which occasionally extended to conchal bone, resulting in osteomyelitis. Multiple bacterial abscesses were seen in the spleen of one mouse. Histological lesions were not detected in control mice or in eight infected mice. S. equi was re-isolated from the nares of fourteen of the twenty two affected mice but not from the eight unaffected challenged mice or control mice. The close resemblance of this model to strangles in horses may justify its further use for the investigation of pathogenesis and protective immunity.