Assessment of the Association between Gross and Histopathological Lesions of Chronic Respiratory Disease and Molecular Detection of Mycoplasma gallisepticum by PCR in Chicken

Aim: To study the gross & histopathological lesions in suspected cases of chronic respiratory disease and to correlate the gross chronic respiratory disease (CRD) lesions & molecular detection of Mycoplasma gallisepticum by polymerase chain reaction (PCR). Methodology: The study was conducted in 40 organized poultry farms in and around Hassan, Karnataka during the year 2022-23. A total of 159 birds of different age groups showing respiratory signs were subjected for post mortem examination and birds with gross lesions in the air sacs, sinuses, trachea and lungs as described by Ley (2008) were considered as cases of CRD and scoring was done based on the severity of lesions in the air sacs. Tissue samples from such birds were subjected to thorough histopathological evaluation to record the microscopic lesions of CRD. The pooled samples from each of the 40 flocks were subjected to PCR to detect the presence of Mycoplasma gallisepticum and to correlate the characteristic lesions with molecular detection of MG. The association between gross CRD lesions and molecular detection of MG by PCR, was estimated by Fisher’s exact test. Results: 108 birds from 27 farms showed gross lesions viz., catarrhal rhinitis, sinusitis, tracheitis with congestion, hemorrhages & catarrhal exudation, bronchitis with accumulation of caseous material, congestion & consolidation of lungs, and cloudy airsacculitis with deposition of cheesy caseous exudates suggestive of CRD. Histopathological findings revealed moderate to severe catarrhal rhinitis, mucopurulent to severe purulent sinusitis, moderate to severe airsacculitis, moderate to severe catarrhal/hemorrhagic tracheitis, and moderate to severe bronchopneumonia. Out of the 40 flocks, eight flocks were found positive for MG infection by PCR indicating an occurrence rate of 20%. The flocks that tested positive for MG by PCR were among the 27 flocks with characteristic CRD lesions. Conclusion: There exists a significant positive association between gross CRD lesions and molecular detection of MG by PCR and PCR could be used for early detection of MG infections in chicken.