Investigating bovine coronavirus in Indian calves: Incidence, molecular evidence, and pathological role in bovine respiratory disease complex (BRDC)

Background: Bovine coronavirus (BCoV) and bacterial pathogens contribute to bovine respiratory disease complex (BRDC) in young calves. However, the role of BCoV in BRDC occurrence and site-specific respiratory pathology in India remains poorly explored. Aims: This study aimed to assess BCoV prevalence in BRDC cases. Methods: We investigated 406 weaner calves (166 cattle, 240 buffaloes) up to <= 1 year, with respiratory distress and pulmonary lesions. Results: BRDC cases exhibited 0.98% BCoV occurrence, confirmed by partial N gene amplification (172 bp) via RT-PCR and immunohistochemistry (IHC). Grossly, 4 BCoV positive cases showed variable degrees of consolidation of cranioventral lobes and non-collapsed caudodorsal lobes, associated with congestion and emphysema. Microscopically, the inflated sites of the lung tissue sections showed hallmark changes of interstitial pneumonia characterized by moderate infiltration with lymphocytes and increased numbers of fibroblasts in the interalveolar septa and the stroma of bronchioles and bronchi. In concomitant Pasteurella multocida infected cases, cranioventral lobes exhibited suppurative bronchopneumonia with neutrophilic exudate. The above lesions were well colocalized with BCoV antigen in the epithelial cells and in the debris of the lumen of the alveoli and the bronchi/bronchioles. The sequence comparison of the 172 bp amplicon with the published BCoV N gene showed close relatedness. Conclusion: The present study implicated BCoV as a component of BRDC in India that should be considered in the diagnosis of BRDC outbreaks.