Digital necrobacillosis in Norwegian wild tundra reindeer (Rangifer tarandus tarandus)

Abstract

Outbreaks of digital necrobacillosis in Norwegian wild tundra reindeer (Rangifer tarandus tarandus) are described. The outbreaks occurred in late summer and autumn 2007 and 2008, subsequent to periods with an unusually high number of days with precipitation and high air temperature. Lesions were generally restricted to one foot and the disease incidence was highest in calves. Single limbs from 20 animals and six whole carcasses were submitted for laboratory examination. Gross lesions were characterized by swelling of the fetlock to coronary band area and cutaneous sinus tracts with sparse discharge of pus. Subcutaneous tissue was inflamed and oedematous with focal necrosis. Tendons, tendon sheaths, joints and periosteum of the digital bones were often affected. Animals shot during winter showed severe chronic periostitis and osteomyelitis and necrotizing deforming arthritis. Microscopically, skin lesions were characterized by deep ulcers with centrally located necrotic tissue, bordered by a zone of oedema and intense inflammation with granulation tissue and fibrosis. Necrosis, suppurative inflammation and oedema were found in the synovial membranes, tendons and tendon sheaths. Digital bone lesions were characterized by necrosis, fibrosis and extensive bone proliferation. Vasculitis and thrombosis were common in all lesions. Elongate filamentous gram-negative bacteria in necrotic lesions from all animals were identified as Fusobacterium necrophorum by fluorescence in-situ hybridization. F. necrophorum was cultured from the foot lesions of six animals. Five of these isolates were examined by 16S rRNA sequencing. The sequences were identical and differed from all other strains listed in GenBank. These results are consistent with circulation of a reindeer-adapted pathogenic strain of F. necrophorum in the wild reindeer population, causing outbreaks of digital necrobacillosis following warm and humid summers.