Figure 2. Lesions in the Eustachian tubes were common in calves infected by the oral route.

The severity of lesions was assessed using a subjective scoring system. Four of the 8 orally infected calves had lesion scores ≥2 (of a possible 3) in at least one Eustachian tube, with 3 calves having eustachitis in both ears. Two of the five transtracheally-inoculated calves however developed eustachitis, but were less severe than in orally-inoculated calves (lesion scores of 2 in one Eustachian tube). Examples of the range of lesions and their associated scores are: a) Grade 1 demonstrating curved dorso-medial cartilaginous support of the Eustachian tube. 2× magnification. b) Grade 1 lesion demonstrating columnar ciliated epithelium with loose collections of mononuclear cells in lamina propria. Cellular debris is visible in the lumen. 60× magnification. c) Grade 2 lesion demonstrating moderately dense collections of lymphocytes and plasma cells, with rare neutrophils. Low numbers of lymphocytes are present in the mucosal epithelium. 40× magnification. d) Grade 3 lesion demonstrating dense collections of lymphocytes and plasma cells intermixed with neutrophils in the lamina propria. The superficial mucosal epithelium is focally cuboidal and eroded, and the lumen contains collections of eosinophilic necrotic inflammatory debris. 40× magnification.