Pathological and molecular investigation of complex chronic respiratory disease (CCRD) in a broiler farm

Bacterial infections are a major source of concern for poultry farmers, resulting in significant financial losses each year. Mycoplasma gallisepticum (M. gallisepticum) is one among the major virulent avian pathogens, causing massive economic losses. It causes chronic respiratory disease in chickens, which, when complicated by secondary bacterial invasion by Escherichia coli (E. coli), results in a more complicated disease with severe mortality. In this study, a total of 55 dead broiler birds were examined at the Division of Pathology, ICAR-IVRI, Izatnagar, Uttar Pradesh, to ascertain the cause of death. A mortality rate of about 8.83% (2,320) was recorded in the past 11 days at a broiler farm in Bareilly, Uttar Pradesh, with an overall flock strength of about 20,500 birds. Clinical signs of general depression, inappetence, and respiratory affections were evident. Grossly, most cases revealed thickened and vascularized air sacs, diffuse fibrin deposits over the pericardium and Glisson’s capsule of the liver, along with congested and enlarged primary and secondary lymphoid organs. Microscopically, the liver revealed severe necrosis of hepatocytes with fatty changes and severe lymphoid cell depletion was observed in the immune organs. Special staining procedures, viz., modified Brown and Brenn and Masson’s trichrome, revealed the presence of Gram-negative bacterial colonies and fibrin deposition in the splenic white pulp, respectively. Molecular analysis by polymerase chain reaction (PCR) was carried out by targeting genes of iron and 16S rRNA, which resulted in the confirmation of concurrent infection of M. gallisepticum and E. coli in 50 dead birds.