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Title: Mycoplasma gallisepticum: Control by live attenuated vaccines

item Evans, Jeffrey - Jeff
item Branton, Scott

Submitted to: Lohmann Animal Health Newsletter
Publication Type: Popular Publication
Publication Acceptance Date: 1/25/2012
Publication Date: 3/15/2012
Citation: Evans, J.D., Branton, S.L. 2012. Mycoplasma gallisepticum: Control by live attenuated vaccines. Lohmann Animal Health Newsletter. 1.

Interpretive Summary: Mycoplasma gallisepticum (MG) is a major respiratory pathogen to poultry species (chickens and turkeys) worldwide. In the United States alone, economic losses associated with MG infections are significant and have exceeded $150 million annually. Current strategies to control against MG infections include the use of attenuated strains of MG which are approved for use as vaccines in the egg layer industry and have been demonstrated to reduce losses associated with virulent MG challenges. Among the attenuated strains commercially available, there are two derivatives of an historic MG isolate which was characterized of low or moderate virulence. While one of the derived vaccines has been available for some time and has been the subject of numerous investigations, the other has only recently become commercially available and accordingly, lacks associated research. Research has also demonstrated that MG characteristics may vary over time and by method of propagation. Toward this end, a study was performed to compare the efficacy of derivatives of the historic isolate; the two commercially available vaccines and a laboratory-maintained derivative. Upon vaccination of layers with the derivatives at one of four levels, efficacy was assessed by post-vaccination seroconversion rates and by post-virulent MG challenge protection from airsacculitis. In addition, associated in vivo populations were determined. Research indicated that all of the derivatives were associated in a dose-dependent manner with seroconversion, in vivo populations, and protection against virulent MG-induced disease. This research substantiates the protection associated with all three derivatives of the historic isolate and in particular, provides documentation of efficacy associated with the newly available vaccine.

Technical Abstract: Commercially available attenuated strains of Mycoplasma gallisepticum (MG) are commonly used within the layer industry to control MG-induced mycoplasmosis. 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 non-commercial laboratory-derived F strain isolate was included in the study. Commercial (Hy-Line W-36) layers were placed in biological isolation units at 9 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, 10-1X, 10-2X, or 10-3X). For the commercially available F strain derivatives, 1X equaled the manufacturer’s recommended dose. The 1X dose of the laboratory-maintained F strain derivative equaled 20 uL of a 48 h culture. For wks 1-6 post-vaccination (p.v.), sera was collected weekly from each bird and seroconversion was assessed via serum plate agglutination (SPA). Virulent MG (strain Rlow) challenge occurred via intratracheal inoculation at 7 wks p.v. Necropsies were subsequently performed to assess challenge-associated airsacculitus. For each F strain derivative applied at 1X and 10-1X, 100% seroconversion, as measured by SPA, was demonstrated by 6 wk p.v., while rates at the 10-2X dosage were 10% and 90% for the commercial vaccines and 60% for the laboratory-derived strain at this time period. Following challenge, airsacculitis was observed in 67% of the non-treated controls, but not in any 1X or 10-1X-treated bird independent of applied F strain derivative. A level of protection against airsacculitis was observed among 10-2X and 10-3X-treated birds, but varied by treatment.