The response of chickens to experimental infection 'em ovo' with Mycoplasma synoviae

Embryonated chicken eggs were inoculated at 18 days of incubation with a broth culture of Mycoplasma synoviae and the infected chicks were hatched and reared in isolation. Control chicks were hatched following inoculation of eggs with sterile mycoplasma broth. Both groups were closely observed for clinical signs and, at intervals up to 6 weeks infected and control chicks were killed and examined for gross lesions and for isolation of M. synoviae. Four of the 35 infected chicks developed synovitis but there were no other clinical signs. Airsacculitis was encountered in 44% of birds at postmortem examination but M. synoviae was not consistently isolated from affected air sacs. The organism was recovered most frequently from the trachea and lung but sporadic isolations were made from other sites including infraorbital sinus, heart, kidney, liver, spleen and blood. M. synoviae was also isolated consistently from the tracheas of 10 live infected birds until the end of the experiment at 23 weeks. However, the serum plate agglutination test, using a commercial antigen was positive for only half these birds up to ten weeks, and it was not until 15 and 23 weeks that 90% to 100% of the samples were positive.