Sivaseelan, S.Balasubramaniam, G.A.Balasubramaniam, A.Thilagavathi, K.TANUVAS2018-02-072018-02-072015http://krishikosh.egranth.ac.in/handle/1/5810040535TNV_THE_Y2015_MVN13022The prevalence and pathology of Mycoplasma gallisepticum and its combined pathogens among laying chicken in Namakkal region was studied. Sixty five commercial layer farms situated in and around Namakkal region with the history suggesting Mycoplasma gallisepticum infection were investigated for a period of one year (May 2014 to April 2015). Out of these, 36 farms were positive for MG and these occurred in different combinations of pathogens. Out of 36 farms, Mycoplasma gallisepticum alone was detected in 8 farms (22.22 per cent). The remaining 28 farms (77.78 per cent) were affected by MG with different combinations of concurrent infections like Escherichia coli, Avibacterium paragallinarum, Pasteurella multocida and Ornithobacterium rhinotracheale. The highest incidence of MG with combined infections were observed in the age group of 19 – 30 weeks (58.33 per cent) and in the month of December- 8 farms (22.22 per cent). The season- wise incidence of MG was highest during winter (Dec, Jan and Feb; 50.00 per cent). The highest mortality was observed in MG combined infection with E. coli and Pasteurella multocida (11.76 per cent). The layer chicken affected with MG showed respiratory distress, tracheal rales, increased lachrymation, nasal discharge, coughing and sneezing. The MG with combined infections showed reduced feed consumption, loss of body weight, decrease in egg production, mortality in later stage of diseases, swelling of facial skin and eyelids, and swollen comb and wattle. Grossly, MG affected birds showed catarrhal inflammation of trachea and bronchi, slight pneumonic changes in lungs, cloudiness, airsacculitis and caseous exudate in thoracic air sacs. Severely affected birds showed congestion and haemorrhages in lungs, caseous mass in both thoracic and abdominal air sacs and congested liver with petechial haemorrhages. In MG with E. coli combined infection, the affected birds showed fibrinous pericarditis and perihepatitis. Birds affected with MG and P. multocida combined infections showed multiple miliary necrotic areas in the liver. In MG with A. paragallinarum combined infection the affected birds showed bilateral infraorbital swelling. Cytological smears of CRD affected lung showed increased number of lymphocytes and macrophages. Histopathologically, focal destruction of superficial cells, goblet cell formation, hyperplasia of mucosal epithelium, submucosal infiltration of more number of lymphocytes, macrophages along with haemorrhagic areas were observed in the trachea of exclusive MG infection. Lungs revealed interstitial haemorrhage, parabronchiolar oedema, mucosal hyperplasia of secondary bronchiole and interstitial pneumonia characterised by thickening of interstitium. In the air sacs, increased thickness due to proliferation of submucosal connective tissue with fibroblasts, congested blood vessels, destruction of superficial epithelium and neovascularization in the connective tissue area were observed. The severity of microscopic lesions was intensified depending upon the number of combinations of various pathogens. More severe damage to the respiratory organs and corresponding mortality rate were noticed in MG, E. coli and P. multocida infections, and MG, E. coli and O. rhinotracheal infections. MG positive antigen was detected in the cilia of surface epithelium of trachea, parabronchiolar epithelium of lungs and surface epithelium of air sacs by immunoperoxidase tests. The positive reaction was seen as brown or red precipitates by DAB and AEC chromogen respectively.en-USVeterinary ScienceVeterinary PathologyThesis