Pathological alterations and molecular-immunohistochemical detection of bovine respiratory syncytial virus in dairy calves of Himachal Pradesh, India: a first study
摘要
The dairy industry in India is emerging as one of the key agribusiness sectors, significantly contributing to the national economy. However, despite its high significance, the dairy business is vulnerable to various diseases. The bovine respiratory syncytial virus (BRSV) is the most common viral infection affecting the respiratory system, especially in calves. The association of BRSV with the development of pneumonia is well-established globally; however, only limited research has been conducted on its prevalence and associated pathology in India. This study aims to investigate the pathology and prevalence of BRSV among bovine calves under one year of age. Thirty calves necropsied from June 1st, 2021, to June 30th, 2022, were included in the research to investigate BRSV pathology using cytological, gross, histopathological, and immunohistochemical examinations. A total of 228 samples were collected for BRSV detection, comprising 30 tissue samples from necropsy, 130 samples from clinically ill calves (121 nasal and 9 ocular swabs), and 68 nasal swabs from apparently healthy calves. In cases where BRSV was detected, the main gross findings during necropsy were cranioventral consolidation, rubbery and non-collapsing lungs having rib impressions. Histopathologically, necrotising bronchiolitis and bronchitis, thickening of the interalveolar septa, and multiple numbers of syncytial cells in the alveolar lumen, along with the infiltration of inflammatory cells, mainly lymphocytes, were evident. The cytological examination revealed multi-nucleated cells along with the infiltration of inflammatory cells, mainly lymphocytes. Immunohistochemical examination revealed the presence of viral antigen in syncytial cells along with cells from the bronchial and bronchiolar epithelium, including inflammatory cells, predominantly macrophages. The prevalence of BRSV was found to be 50% (15/30; 95% CI: 33.2–66.8) in necropsied samples and 23.73% (47/198; 95% CI: 18.0–30.3) in clinical samples tested by nested RT-PCR targeting the nucleoprotein (N) gene having an amplicon size of 435 bp. This study concludes that BRSV causes significant morbidity and mortality in bovine calves and requires timely diagnosis and management to prevent heavy economic losses.