Pathology of Mycoplasma gallisepticum infection in naturally infected layer birds

Sixty five commercial layer farms with lesions suggestive of respiratory problem were investigated during the study period from May 2014 to April 2015 to evaluate the pathology of Mycoplasma gallisepticum infection in laying chicken. Mycoplasma gallisepticum was confirmed through PCR in 36 out of 65 farms. The positive farms were examined for gross and histopathological changes in tissues like trachea, lungs, air sacs and liver. The highest incidence of MG infection occurred during the winter season. Grossly, MG affected birds showed catarrhal inflammation of trachea and bronchi, slight pneumonic changes in lungs, cloudiness, air sacculitis and caseous exudate in thoracic air sacs, congestion and haemorrhages in lungs, caseous mass in both thoracic and abdominal air sacs. Histopathologically, focal destruction of superficial cells, goblet cell formation, hyperplasia of mucosal epithelium, submucosal infiltration of lymphocytes, macrophages along with haemorrhagic areas were observed in the trachea. Lungs revealed interstitial haemorrhages, parabronchiolar oedema, mucosal hyperplasia of secondary bronchiole and interstitial pneumonia characterized by thickening of interstitium. Air sacs showed epithelial destruction and increased thickening due to proliferation of submucosal connective tissue with congested blood vessels and neovascularization. This study proved that MG infection occurs severely among laying chicken causing more economic loss to the farmers.