Granulomatous pneumonia due to metastrongylus species associated with <i>Mycoplasma hyopneumoniae</i> and <i>Pasteurella multocida</i> in slaughtered pigs

Abstract

Pneumonia has been identified as one of the limiting factors to pig production. Some of the pneumonia-inducing agents include Mycoplasma hyopneumoniae (MHYO), the primary cause of enzootic pneumonia and Metastrongylus species. which are widely distributed lungworms commonly found in indigenous free-range pigs. This paper describes the pathological findings of 6 cases out of 204 lungs randomly collected from slaughtered pigs in Southwest Nigeria. Samples of the lungs were collected from the cases for bacterial culture, histopathology and detection of MHYO antigens using immunohistochemisty. Gross lesions were severe acute lobular bronchopneumonia (104/204, 50.98%) and greyish discrete nodules in the lungs. Microscopically, there were varying degrees of lymphoid hyperplasia of bronchial-associated lymphoid tissue (BALT) (82.2%), suppurative bronchiolitis with widespread bronchiolar epithelial cells necrosis (57.4%) and granulomatous bronchopneumonia with presence of Metastrongylus spp. and bronchiolar intraluminal cellular exudate consisting predominantly of eosinophils (2.9%). Pasteurella multocida was the most isolated bacterial pathogen (49.0%) either as a single pathogen or in combination with other pathogens from the infected lung samples. Immunohistochemical labelling showed strong MHYO antigens on the surface of bronchial epithelial cells in infected lungs (86/204). This is the first report of granulomatous bronchopneumonia due to Metastrongylus spp. associated with a co-infection of MHYO and Pasteurella multocida in Nigerian indigenous pigs. It is suggested that metastrongylosis may be more common than reported in this study. The detection of respiratory pathogens such as Mycoplasma. hyopneumoniae, Metasrongylusspp. and Pasteurella multocida suggest that they are potential contributors to bronchopneumonia observed in this study.