Pathogenicity of Bibersteinia trehalosi in bovine calves

Abstract

<p><strong>Introduction</strong> - <em>Bibersteinia trehalosi</em> has been associated with respiratory disease in ruminants particularly in wild and domestic sheep. Recently, there has been an increased interest in <em>B. trehalosi</em> isolates obtained from diagnostic samples from bovine respiratory disease cases. This study evaluated the role of <em>B. trehalosi</em> in the bovine respiratory disease complex using an intra-tracheal inoculation model in calves. This study also evaluated the potential of haptoglobin-matrix metalloproteinase 9 (Hp-MMP 9) serum concentrations as a useful diagnostic tool in calves affected with <em>B. trehalosi</em> and <em>M. haemolytica</em> associated respiratory disease.</p> <p><strong>Materials and Methods</strong> - Thirty-five cross-bred dairy steers were inoculated intra-tracheally with either leukotoxin negative or leukotoxin positive <em>B. trehalosi</em>, <em>Mannheimia haemolytica</em>, a combination of leukotoxin negative <em>B. trehalosi</em> and <em>M. haemolytica</em>, or negative control. Physical examinations were conducted and serum samples were collected throughout the study. Calves were euthanized and necropsies performed on day 10 of the study.</p> <p><strong>Results</strong> - No significant differences were found between the groups of calves challenged with <em>B. trehalosi</em> alone or in conjunction with <em>M. haemolytica</em> and the negative control calves with respect to percent lung involvement, rectal temperature, respiratory or depression score, or serum Hp or Hp-MMP 9 concentration in this study. <em>M. haemolytica</em> inoculated calves, but not <em>B. trehalosi</em> inoculated calves had increased lung involvement compared to control calves. <em>B. trehalosi</em> was only cultured once from the lungs of inoculated calves at necropsy. Increases in serum Hp and Hp-MMP 9 concentrations for the <em>M. haemolytica</em> group became significantly different from other groups on day 7. The leukotoxin positive <em>B. trehalosi</em> group demonstrated increased serum Hp-MMP 9 concentrations on days 3-10 compared to pre-inoculation concentrations.</p> <p><strong>Conclusions</strong> - Based on these findings <em>B. trehalosi</em> may not be a primary pathogen of respiratory disease in cattle. Culture of <em>B. trehalosi</em> from diagnostic submissions should not be immediately identified as a primary cause of respiratory disease. Serum Hp-MMP 9 concentration is a useful diagnostic tool for detecting early pulmonary inflammation in calves challenged with <em>B. trehalosi</em> and <em>M. haemolytica</em>. Serum Hp-MMP 9 may also be a useful tool in detecting subclinical pulmonary inflammation in challenged calves.</p>