MYCOPLASMAS IN THE ETIOLOGY OF MULTIFACTORIAL RESPIRATORY-DISEASE

The avian mycoplasmas pathogenic for commercial poultry, Mycoplasma ga llisepticum and Mycoplasma synoviae in chickens and turkeys, and Mycop lasma meleagridis and Mycoplasma iowae in turkeys are egg-transmitted infections and exhibit wide variations in clinical manifestations. Myc oplasma gallisepticum strains vary widely in virulence, tissue tropism , and antigenic makeup and have the ability to alter the expression of major surface antigenic proteins. Although less well studied, strains of M. synoviae, M. meleagridis, and M. iowae appear to exhibit simila r variability. Intraspecies variability among mycoplasma strains and t heir ability to interact with other disease-producing factors explain the wide variability of clinical manifestations, difficulties in diagn osis,their ability to persist within the host for long periods of time , and many of the difficulties involved in control and eradication pro grams. Mycoplasmas are also well known for their interactions with oth er infectious agents and environmental factors in producing clinical d isease. Control of the clinical manifestations of Mycoplasma infection s is simplified when concurrent infections are minimized and optimum e nvironmental conditions are provided.