Major bacterial pathogens of bovine respiratory disease and lung lesions in calves from selected areas of Ethiopia

Abstract

Bovine respiratory disease (BRD) is a potential threat and an economically detrimental disease of calf-rearing in Ethiopia. This study was designed to isolate the major bacterial pathogens associated with respiratory disease of calves and the lung lesions involved. A crosssectional study with a purposive sampling method was employed in 170 calves during the study period from April 2018 to October 2018. The Bacteriological and molecular assay revealed overall isolation of 156 (91.76%) bacterial pathogens. Gross inspection of pneumonic lungs revealed one or more lesions of hydatidosis (46.67%), emphysema (44.44%), congestion (35.56%), hemorrhage (20.0%) and atelectasis (15.56%). Bacterial pathogen identification showed 86 (50.59%) Mannheimia haemolytica, 31 (18.24%) Pasteurella multocida, 22 (12.94%) Bibersteina trehalosi and 17 (10.0%) Histophilous somni. The distribution of bacterial pathogens in the study areas indicates a higher incidence of M. haemolytica from the nasopharyngeal swab and pneumonic lung tissue at a rate of 68 (61.26%) and 18 (40.0%), respectively. Multiplex PCR of M. haemolytica revealed amplification of the PHSSA gene (~325 bp) and Rpt2 gene (~1022 bp). Conventional PCR assay of P. multocida showed amplification of the speciesspecific KMT1 gene (~460 bp) and B. trehalosi targeting sodA gene (~144 bp). The findings in the present study indicate that M. haemolytica is the major bacterial pathogen of BRD in calves in the study areas. Thus, it calls for the development of a vaccine from M. haemolytica strains and assessment of pathogen-specific risk factors associated with BRD in calves to design cost-effective control strategies.