Apparent re-infection of enzootic-pneumonia-free pig herds: specificity of diagnosis.

In a control scheme for enzootic-pneumonia-free herds, 43 herds developed enzootic pneumonia, as judged by non-specific clinical and pathological criteria over 10 years. Material for cultural examination was obtained from 32 of these outbreaks, and Mycoplasma suipneumoniae was identified in 28 of them. The four failures occurred before 1971 at a time when the cultural techniques were clearly inferior. Since 1971 M suipneumoniae has been isolated from all the 17 outbreaks sampled for this purpose. Two of the outbreaks from which M suipneumoniae was not recovered, and three further outbreaks, were closely connected with outbreaks from which M suipneumoniae had been isolated (to make 33 out of 35). The remaining eight outbreaks (in which isolations of M suipneumoniae were not attempted) were clinically and pathologically consistent with the pattern of the others. Hence, there is reason to believe that during this period the outbreaks of respiratory disease simulating enzootic pneumonia in the control scheme have probably all been associated with the presence of M suipneumoniae.