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A comparative study of live attenuated F strain-derived Mycoplasma gallisepticum vaccines
J D Evans1, S A Leigh, J L Purswell
1USDA, Agricultural Research Service, Poultry Research Unit, Mississippi State, MS 39762, USA. jeff.evans@ars.usda.gov
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 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, 1x equaled the manufacturer's recommended dose. The 1x dose of the noncommercial laboratory-maintained F strain derivative equaled 20 microl 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.
Insights
Commercially available Mycoplasma gallisepticum (MG) vaccines effectively induce seroconversion and protect against airsacculitis. Even at reduced doses, these vaccines offer significant protection for commercial layers.
Area of Science:
- Veterinary Immunology
- Poultry Health
- Bacteriology
Background:
- Mycoplasma gallisepticum (MG) causes significant economic losses in the layer industry due to mycoplasmosis.
- Live attenuated MG vaccines, particularly F strain derivatives, are widely used for disease control.
- Variability in vaccine efficacy necessitates comparative studies of available F strain derivatives.
Purpose of the Study:
- To compare commercial F strain-derived MG vaccines against a laboratory-derived isolate.
- To evaluate vaccine-induced seroconversion, in vivo persistence, and protection against virulent MG challenge.
- To determine the efficacy of different vaccine dosage levels.
Main Methods:
- Commercial Hy-Line W-36 layers were vaccinated via eye-drop with three F strain derivatives at varying doses (1x, 10(-1)x, 10(-2)x, 10(-3)x).
- Seroconversion was monitored weekly using serum plate agglutination (SPA) from 1 to 6 weeks post-vaccination.
- Birds were challenged intratracheally with virulent MG (strain R(low)) at 7 weeks post-vaccination, followed by necropsy to assess airsacculitis.
Main Results:
- 100% seroconversion was achieved by 6 weeks post-vaccination with 1x and 10(-1)x doses of all F strain derivatives.
- Lower doses (10(-2)x) showed variable seroconversion rates: 10-90% for commercial vaccines and 60% for the laboratory strain.
- No airsacculitis was observed in birds treated with 1x or 10(-1)x doses, while 66.67% of unvaccinated controls developed airsacculitis.
Conclusions:
- Commercial F strain-derived MG vaccines elicit robust seroconversion and provide complete protection against virulent MG-induced airsacculitis at recommended and 10-fold reduced doses.
- The laboratory-derived F strain isolate also demonstrated efficacy, though seroconversion varied at lower doses.
- These findings support the use of current commercial MG vaccines for effective mycoplasmosis control in layer flocks.
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