Retrospective study of swine respiratory diseases in Ogun and Oyo States, Nigeria: Immunohistochemical detection of <i>Mycoplasma hyopneumoniae</i>

Swine respiratory diseases particularly enzootic pneumonia caused by Mycoplasma hyopneumoniae (Mhyo) constitutes a significant health problem to pig production in many countries. However, the impact has been underestimated in Nigeria. This study therefore, retrospectively analyzed swine respiratory diseases and the associated pulmonary histopathology. Postmortem records and archival lung samples were obtained from the Departments of Veterinary Pathology University of Ibadan, Ibadan and Federal University of Agriculture, Abeokuta. A total of 98 pig carcasses were presented for necropsy during the period between 2005 and 2017. The diseases presumptively diagnosed using gross morphological criteria were extracted from the postmortem records while, 21 formalin-fixed archival lung samples were used for histopathology and immunohistochemistry using standard techniques. Data were analysed using descriptive statistics while Chi Square was used to test for association between different variables and pulmonary lesions at α0.05. In this study, respiratory diseases had a prevalence of 56.1% with enzootic pneumonia as the most frequently diagnosed at postmortem (49%, 48/98). Only age was identified to be a significant (P = 0.019) predisposing factor in the development of respiratory diseases. Microscopically, hyperplasia of bronchus associated lymphoid tissue (BALT) with formation of lymphoid nodules and thickening of alveolar septa were the most significant changes (38.1%, 8/21). Immunohistochemically, M. hyopneumoniae antigen was detected in 13/21 (61.9%) of the lung samples and were immunolabelled as granular brown reactions on the luminal surfaces of bronchial and bronchiolar epithelial cells and intraluminal cellular exudates within the airways. The histopathological findings and the detection of M. hyopneumoniae antigen indicated that the organism is primarily involved in the development of enzootic pneumonia in naturally infected pigs and may be central in the pathogenesis. It is concluded that enzootic pneumonia is a serious health issue in pigs in the study area and needs urgent attention. Keywords: Archival lung samples, Histopathology, Pigs, Pneumonia, Retrospective analysis