During a period of 1979 to 1985, a total of 280
Mycoplasma gallisepticum (MG) strains were isolated from 228 diseased layer chickens housed on 51 commercial farms in varying geographical areas of Japan. Of 55 chicken flocks investigated, 45 showed respiratory symptoms and 10 were affected with synovitis.
The 45 flocks consisted of 11 flocks of 50 growing chickens and 34 flocks of 131 adult chickens. They were characteized by nasal discharge, catarrhal exudate in the trachea, and airsacculitis, but never synovitis. Facial edema was also observed in adult chickens mainly in the case of mixed infections with
Haemophilus paragallinarum. The chickens of this group had a high level of hemoagglutination inhibiting titer against MG. The organism was isolated frequently from the nasal cavity and trachea, and occasionally from the air sacs, but never from any joint.
The 10 flocks with synovitis consisted of in 8 flocks of 36 growing chickens and 2 flocks of 11 adult chickens. They were characterized by swelling of the hock joint and/or breast blisters, and few of them showed respiratory symptoms. In them, MG was frequently isolated from hock joint, breast blisters, nasal cavity, and tracheas.
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