Diagnostic Strategies and Strain Typing for Johne's Disease in Wood Bison (Bison bison athabascae)

Cattle diseases are considered a major threat to wood bison (Bison bison athabascae) conservation. Johne's disease (JD) is a chronic infectious enteritis caused by Mycobacterium avium subspecies paratuberculosis (Map), that affects domestic and wild ruminants globally and could negatively impact wood bison health. Clinical manifestation of JD in free-ranging or captive wood bison has not been documented. We studied animals in a captive wood bison herd in Alberta, Canada 1) to detect Map in bison clinically suspected of Johne's disease, by histopathology, quantitative PCR (qPCR), and isolation by culture; 2) to identify optimal tissue samples for Map detection; and 3) to identify the strain(s) of Map isolated. Six wood bison were evaluated with clinical signs suggestive of JD. We performed necropsies within 24-48 h after euthanasia and collected 24 tissue samples from each bison. At necropsy, no evidence of thickening or corrugation of the intestinal mucosa was observed in any bison. On histopathologic examination, granulomatous lesions with acid-fast bacilli were more frequent in the paracortex of the midjejunal lymph node (LN) and distal jejunal LN, followed by ileal LN, in comparison to the rest of the tissue samples evaluated. In general, tissue culture had the highest proportion of positive samples, with 62.5% (90/144) of positive samples, followed by F57/IS900 qPCR with 43.1% (56/130), and histopathology with 29.0% (38/131). We concluded that distal jejunum and its associated lymph nodes were the most reliable tissue samples for detecting Map, regardless of tissue autolysis or the absence of visible gross lesions. Finally, using IS1311 PCR-restriction enzyme analysis and single-nucleotide polymorphisms, we identified a type II (cattle) strain, secondary clade, in tissue samples. These findings have practical relevance for field necropsies as they provide evidence to direct selection of preferred sampling sites to detect Map in wood bison and to choose appropriate diagnostic techniques.