Mannheimia granulomatis-Infected Pyogranulomatous Oral Lesions with Concurrent Amyloidosis in Roe Deer (Capreolus capreolus) in France.

Mannheimia granulomatis-associated lesions have been poorly described compared with those associated with other members of the Pasteurellaceae family; they include pneumonia, panniculitis, and keratoconjunctivitis in domestic and wild ruminants and hares. We describe 15 cases of roe deer (Capreolus capreolus) showing M. granulomatis-infected oral lesions that were detected in France between 2016 and 2023. Comprehensive necropsies were performed, with additional analyses based on findings. All deer were >15 mo of age on the basis of tooth eruption. They were thin (1/15), cachectic (13/15), or of unknown body condition (1/15). They exhibited multiple cryptic millimetric to centimetric caseous granulomas within the lips, tongue, or cheeks (13/15); pyogranulomatous lymphadenitis of a mandibular lymph node (1/15); or necrosuppurative mandibular osteomyelitis with bone proliferation (1/15). Histopathologically, oral lesions of 10/15 animals showed multifocal, severe, chronic pyogranulomatous cheilitis, glossitis, or stomatitis with intralesional Gram-negative bacterial colonies lined by Splendore-Hoeppli material. Amyloidosis was detected in 4/11 animals for which tissues were submitted for microscopic examination, affecting the abomasum, the spleen, and a minor salivary gland in, respectively, 4/6, 3/5, and 1/8 animals for which the relevant organs were assessed histologically. Amyloid deposits showed strong immunoreactivity with a murine monoclonal antibody directed against amyloid AA. AA amyloidosis, never previously described in roe deer, was considered secondary to chronic inflammation. Mannheimia granulomatis was cultured and identified biochemically or by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in oral lesions of all individuals. Coinfection with other bacterial species was sporadically identified. We considered the chronic emaciation and death of these animals to be multifactorial, involving oral lesions, secondary amyloidosis when present, parasitic infestation of variable severity, and probably environmental factors. Further investigation is needed to understand the epidemiology and pathogenesis of M. granulomatis infection in roe deer, including a possible propensity to emerge as temporal and geographic clusters and to induce AA amyloidosis.