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Immunogenic potency of oil-emulsified Mycoplasma gallisepticum bacterins
Abstract:
Immunogenicity of an aqueous Mycoplasma gallisepticum (MG) bacterin and two oil-emulsified bacterins with aqueous-phase-to-oil-phase ratios of 1:2 and 1:4 were evaluated in 3 groups of 5-week-old MG-free White Leghorn chickens. Group 4 chickens were nonimmunized controls. Group 1, 2, and 3 chickens received primary immunizations with 0.5 ml of bacterin subcutaneously (SC). Six weeks later, half of the vaccinated chickens received a second immunization (0.5 ml SC). Six weeks after the last dose of vaccine, all 4 groups of chickens were challenged intraocularly with a 24-hr broth culture of pathogenic MG ("R' strain). The geometric mean hemagglutination-inhibition antibody titers (GMT) of non-immunized, once-immunized, and twice-immunized chickens were compared at 2-week intervals following primary immunization, secondary immunization, and challenge. Both oil-emulsified bacterins stimulated significantly higher (P less than or equal to 0.05) levels of antibody than the aqueous bacterin after the primary and secondary immunizations. Following challenge with pathogenic MG, the GMT in the immunized and non-immunized chickens approached comparable values. The highest GMT in groups 1, 2, 3, and 4 respectively were: a) primary response, 19, 99, 121, and 11; b) secondary response, 105, 423, 793, and 21; and c) challenge response, 171, 278, 300, and 160. After challenge there was a further rise of antibody level in non-immunized chickens, those immunized with the aqueous bacterin, and those immunized only once with the oil-emulsified bacterins. This suggested a lack of protection against challenge. However, there was no increase of GMT in chickens immunized twice with the oil-emulsified bacterins.
Insights
Two oil-emulsified Mycoplasma gallisepticum (MG) bacterins induced higher antibody titers than aqueous bacterins. However, only twice-vaccinated chickens showed no antibody rise post-challenge, indicating protection.
Area of Science:
- Veterinary Immunology
- Poultry Health
- Bacteriology
Background:
- Mycoplasma gallisepticum (MG) infection poses a significant threat to poultry health and economic productivity.
- Bacterins are commonly used for avian disease prevention, but their immunogenicity can vary based on formulation.
- Understanding the immune response to different bacterin types is crucial for effective disease control strategies.
Purpose of the Study:
- To evaluate and compare the immunogenicity of an aqueous MG bacterin versus two oil-emulsified MG bacterins.
- To assess the antibody response following primary and secondary immunization, and after challenge with pathogenic MG.
- To determine the protective efficacy of different bacterin formulations in White Leghorn chickens.
Main Methods:
- Three groups of MG-free White Leghorn chickens were immunized with aqueous or oil-emulsified MG bacterins (1:2 and 1:4 ratios).
- A fourth group served as non-immunized controls.
- Chickens received primary and, in some cases, secondary subcutaneous immunizations. All groups were subsequently challenged intraocularly with pathogenic MG. Antibody titers (GMT) were measured using hemagglutination-inhibition assays at various intervals.
Main Results:
- Oil-emulsified bacterins elicited significantly higher antibody titers (P ≤ 0.05) compared to the aqueous bacterin after both primary and secondary immunizations.
- Following challenge, GMTs in immunized and non-immunized groups became comparable, except in chickens receiving two doses of oil-emulsified bacterin.
- Non-immunized, aqueous bacterin, and once-immunized oil-emulsified bacterin groups showed increased antibody levels post-challenge, suggesting a lack of protection. Twice-immunized oil-emulsified bacterin groups showed no GMT increase post-challenge.
Conclusions:
- Oil-emulsified Mycoplasma gallisepticum bacterins demonstrate superior immunogenicity, inducing higher antibody titers than aqueous formulations.
- A lack of antibody titer increase post-challenge in chickens receiving two doses of oil-emulsified bacterin suggests effective protection against pathogenic MG.
- The study highlights the importance of bacterin formulation and vaccination regimen in achieving protective immunity against Mycoplasma gallisepticum.