A Comparative Study of Live Attenuated F Strain-Derived Mycoplasma gallisepticum Vaccines

Commercially available attenuated strains of Mycoplasma gallisepticum (MG) are commonly used within the layer industry to control MG-induced mycoplasrnosis. Among these are two live MG vaccines derived from the moderately pathogenic MG chick F strain. In the present study, the commercially available F strain derivatives were compared for their ability to elicit seroconversion, persist in vivo, and protect against virulent MG-induced airsacculitis. In addition, a noncommercial laboratory derived high-passage F strain isolate was included in the study. Commercial (Hy-Line W-36) layers were placed in biological isolation units at 9 wk of age (woa). At 10 woa, birds within each biological isolation unit were treated via eye-drop application with one of the three F strain derived vaccines at one of four levels (1X, 10(-1)X, 10(-2)X, or 10(-3)X). For the commercially available F strain derivatives, IX equaled the manufacturer's recommended dose. The 1X dose of the noncommercial laboratory maintained F strain derivative equaled 20 mu l of a 48 hr culture. For wk 1-6 postvaccination (p.v.), sera were collected weekly from each bird, and seroconversion was assessed via serum plate agglutination (SPA). Virulent MG (strain R-low) challenge occurred via intratracheal inoculation at 7 wk p.v. Necropsies were subsequently performed to assess challenge-associated airsacculitus. For each F strain derivative applied at 1X and 10(-1)X, 100% seroconversion, as measured by SPA, was demonstrated by 6 wk p.v., and rates at the 10(-2)X dosage were 10% and 90% for the commercial vaccines and 60% for the laboratory-derived strain in this period. Following challenge, airsacculitis was observed in 66.67% of the nontreated controls but not in any 1X- or 10(-1)X-treated bird independent of applied F strain derivative.