Refinement of the equine influenza model in the natural host: A meta-analysis to determine the benefits of individual nebulisation for experimental infection and vaccine evaluation in the face of decreased strain pathogenicity.

The study focuses on the investigation of efficacy of individual nebulisation in administering Equine Influenza (EI) vaccine and comparing it to traditional room nebulisation method. The research also analyzes the decreased pathogenicity of recent Florida Clade 2 (FC2) EIV strains and its impact on the statistical power of the studies.

Introduction to the Study

• This research centers around Equine Influenza (EI), a major respiratory disease in horses caused by the H3N8 equine influenza viruses (EIV). Vaccination is a crucial prevention or control strategy for EI.
• However, the virus continually adapts through antigenic drift. This necessitates frequent efficacy evaluations of the numerous commercially available EI vaccines through clinical trials conducted on the natural host, i.e., the horses.
• The study also discusses challenges faced in EI vaccine studies due to potential decrease in pathogenicity observed with recent Florida Clade 2 (FC2) EIV isolates. This decrease led to more diverse clinical responses and virus shedding measured after infection by room nebulisation, thus reducing the statistical power of the studies.

Goals of the Study

• The research aimed at comparing clinical and virological parameters after experimental infection with different EIV strains. This was to confirm the effectiveness of individual nebulisation as a model refinement.
• It also aimed to ensure that the number of animals per group didn’t unnecessarily increase.

Methodology and Outcome

• The study is a retrospective comparison and meta-analysis of clinical and virological results drawn from 9 independent EIV infection studies conducted on the natural host.
• Naïve Welsh mountain ponies were experimentally infected by either room or individual nebulisation with FC2 EIV strains. These include strains such as A/equine/Richmond/1/07 (R/07), A/equine/East Renfrewshire/11 (ER/11), etc.
• The analysis confirmed decreased pathogenicity of the EIV ER/11 and C/12 strains when compared to R/07. The infection using individual nebulisation enhanced the clinical and virological parameters induced by recent FC2 strains in comparison to the room nebulisation.

Conclusion

• The research conclusions advocate the benefits of individual nebulisation as it provides better control of the challenge dose administered. It also results in greater uniformity in the response measured in control animals. This helps to maintain the number of animals per group to the minimum necessary to achieve meaningful results in vaccine efficacy studies.
• In adherence to the 3Rs (Replacement, Reduction and Refinement) principles, individual nebulisation supports responsible scientific research by reducing the number of animals employed in experiments.