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Pathogenicity of Mycoplasma hyopneumoniae strain in Naturally Infected Slaughtered Pigs in Nigeria: Immunohistochemical and Ultrastructural Studies

Enzootic pneumonia caused by Mycoplasma hyopneumoniae (MHYO) remains a serious concern to swine industry in many countries including Nigeria. MHYO strains isolated from different countries and geographical locations are known to vary in pathogenicity in pigs. There is paucity of information on the pathogenicity of MHYO strain affecting pigs in Nigeria. This study investigated the pathogenicity of MHYO strain in naturally infected slaughtered pigs in Nigeria using immunohistochemistry and electron microscopy. Two hundred and sixty four lungs were randomly collected from abattoirs at Abeokuta, Ibadan and Lagos, Southwest Nigeria. A sub‐sample of 104 pneumonic lungs was selected, processed for routine histopathological examination and immunohistochemistry, while 3 lung tissues were selected for ultrastructural studies. The most significant microscopic changes were suppurative broncho‐interstitial pneumonia associated with varying degrees of lymphoid hyperplasia of the bronchus‐associated lymphoid tissue (BALT) and thickening of alveolar septa due to cellular infiltration. Immunohistochemically, MHYO antigens were detected in 86/104 (82.7%) lungs. Bronchial and bronchiolar epithelial cells typically exhibited a granular brown reaction on the surface, in the BALT and luminal cellular exudates of MHYO‐infected lung tissues. Transmission electron microscopy revealed numerous Mycoplasmas in the lumina of respiratory tract, in between degenerated cilia, while a few Mycoplasmas were located within the alveoli. It is concluded that the MHYO strain detected in this study is pathogenic to pigs and capable of inducing pneumonic lesions, and therefore implicated in the pathogenesis. This is the first investigative study on pathogenicity of MYHO strain in slaughtered pigs in Nigeria.