Figure 1. Oral inoculation of calves results in lesions in middle ear.

The severity of lesions in tympanic bulla was assessed using a subjective scoring system. No control or transtracheally-inoculated calf had lesion scores >1 in the tympanic bullae. In contrast, 3 of 8 orally inoculated calves developed significant lesions in the tympanic bullae (lesion score >1, P≤0.05). Two of these animals had bilateral lesion scores ≥3. Examples of the range of lesions and their associated scores are: a) Grade 1 shows normal bony trabecula, thin cuboidal to simple squamous mucosal epithelium and loose acellular lamina propria. 60× magnification. b) Grade 3 lesions demonstrate moderately dense collections of mixed inflammatory cells infiltrating the lamina propria and the mucosal epithelium. Moderate to large numbers of macrophages and neutrophils are present in the lumen. 40× magnification. c) Grade 4 lesions are characterized with a superficial epithelium that is moderately hyperplastic, with regions of squamous metaplasia. There are large numbers of mixed inflammatory cells infiltrating the lamina propria and epithelium. Prominent plump spindle cells and small capillaries lined by plump endothelia are present in the lamina propria. There are luminal collections of inflammatory cells and necrotic debris. 40× magnification. The insert shows large osteoclasts occupying prominent Howships lacunae (arrow) and osteoblasts lining the opposite side of the trabecula, indicative of bone remodeling. 40× magnification. d) Grade 5 lesions show full thickness mucosal necrosis with underlying osteonecrosis of trabecular bone. Note the superficial collections of inflammatory and necrotic debris. 20× magnification.