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Positive and negative aspects of host immune response to Haemophilus, Actinobacillus and Pasteurella
1Veterinary Research Institute, Attwood, Victoria, Australia.
Abstract:
Haemophilus somnus, Actinobacillus pleuropneumoniae and Pasteurella haemolytica are economically important bacteria with pathogenic characteristics that require us to look further than killed, whole cell bacterins for induction of a protective immune response. A strong immune response is not synonymous with protection and the extreme specificity of the immune response works to our disadvantage when broad protection is needed. Detection of animals that are susceptible or immune to infection is important for the purpose of diagnosis and epidemiological study. However serum antibody levels are rarely indicative of protection unless it is known that the antibody of a particular isotype must be directed against a specific epitope for protection to occur. Parenteral vaccination with killed, whole cells of H. somnus, A. pleuropneumoniae or P. haemolytica produces, respectively, adequate protection, partial protection and increased disease. The reasons for these differences and methods of improving protection, based on an understanding of virulence determinants, are discussed.
Insights
Killed whole cell bacterins for Haemophilus somnus, Actinobacillus pleuropneumoniae, and Pasteurella haemolytica offer limited protection. Understanding virulence factors is key to developing improved vaccines against these economically important bacterial pathogens.
Area of Science:
- Veterinary Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Haemophilus somnus, Actinobacillus pleuropneumoniae, and Pasteurella haemolytica are significant economic threats in livestock due to their pathogenic properties.
- Current whole-cell bacterin vaccines provide variable protection, highlighting limitations in inducing broad, protective immunity.
- Assessing animal susceptibility or immunity is crucial for diagnosis and epidemiological studies, but serum antibody levels often do not correlate with protection.
Purpose of the Study:
- To evaluate the efficacy of killed, whole-cell bacterin vaccines against H. somnus, A. pleuropneumoniae, and P. haemolytica.
- To explore the relationship between immune response, antibody levels, and actual protection against these bacterial infections.
- To discuss strategies for improving vaccine-induced protection by understanding bacterial virulence determinants.
Main Methods:
- Parenteral vaccination of animals with killed, whole-cell bacterins of H. somnus, A. pleuropneumoniae, and P. haemolytica.
- Assessment of the level of protection induced by each vaccine.
- Discussion of virulence factors contributing to differential vaccine efficacy.
Main Results:
- Vaccination with H. somnus bacterin resulted in adequate protection.
- A. pleuropneumoniae bacterin conferred partial protection.
- P. haemolytica bacterin vaccination led to increased disease incidence, indicating a lack of efficacy and potential adverse effects.
Conclusions:
- Killed, whole-cell bacterins are insufficient for robust protection against these economically important pathogens.
- The specificity of the immune response can be a disadvantage when broad protection is required.
- Further research into bacterial virulence determinants is essential for developing more effective vaccines and improving animal health strategies.