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Ornithobacterium rhinotracheale (ORT) and Mycoplasma gallisepticum (MG) are bacterial causes of respiratory diseases in chickens. The objective of this work was to investigate the possible interaction between ORT and MG in respiratory problem of broiler chickens. The experimental study confirmed that ORT infection alone could induced respiratory signs as (rales, nasal discharge), post mortem lesions (unilateral and bilateral pneumonia) and histopathological changes in tracheas, lungs and air sacs. Moreover, co-infection of ORT with MG induced severe respiratory signs like pneumonia, edema and severe inflammatory cell infilteration in lungs and air sacs than that observed in chickens infected with ORT or MG alone. ORT and MG were successfully re-isolated by PCR from tracheal swabs at 3, 7 and 14 days post infection. The results showed the synergistic effect of mixed infection of ORT and MG in broiler chickens regarding clinical signs, PM lesions, mortality rate, body weight, reisolation and histopathological examination. [ABSTRACT FROM AUTHOR]

Gallibacterium anatis and Mycoplasma gallisepticum are bacterial pathogens affecting the respiratory tract of broiler chickens. Tracking the mixed experimental infection effect with G. anatis and M. gallisepticum in broiler chickens regarding clinical signs, performance, PM and histopathological lesions was the aim of this work. Birds inoculated with G. anatis (G2) or M. gallisepticum (G4) alone showed less severe clinical signs and gross pathological lesions in the respiratory tract. While, co-infection with G. anatis and M. gallisepticum (G3) exaggerated the clinical signs like rales, sneezing, nasal discharge, coughing, lacrimation and open mouth breathing and also gross and microscopical lesions which appeared as severe conjunctivitis with hemorrhagic congestive tracheitis, pneumonia and hyperplasia of the epithelium lining of trachea as compared to other groups which were infected with single pathogen or control negative group (G1). In conclusion, G. anatis produce less severe clinical signs and lesions regarding respiratory system than coinfection with M. gallisepticum which may be a most important factor enhancing the pathogenicity of G. anatis under field conditions [ABSTRACT FROM AUTHOR]