The effect of heterotypic infections of older horses with equine influenza virus type-2 on some clinical and immunological parameters.

This research studies how vaccinations against one strain of horse flu (equine influenza virus type-2) effects the animals’ response when exposed to other strains of the virus. The study examines how this exposure impacts various clinical and immunological properties of the horses.

Study Design and Method

• The experiment involved fifteen horses, all ten years old. Twelve horses were vaccinated with a vaccine containing antigens of the A-equi-2/Miami/63 virus strain on two days of the experiment.
• Meanwhile, three unvaccinated horses served as a negative control group.
• One horse received a commercially available vaccine containing antigens of both A-equi-2/Miami/63 and A-equi-1/Praha/56, serving as a positive control.
• Some horses in the study were then exposed – or challenged – intranasally to strains of the flu virus. Three were exposed to a strain like the one they were vaccinated against (homotypic strain); six were exposed to different virus strains (heterotypic strains).
• In the negative control group, each horse was exposed to different flu virus strains.
• The horse receiving the commercial vaccine was not exposed to the virus.
• The performance of each virus strain was analysed by replicating it in chick embryos. Blood from the horses was also regularly taken throughout the course of the experiment for in-depth clinical and immunological examination.

Results and Implications

• Statistical analysis revealed that horses vaccinated against the A-equi-2/Miami/63 strain reacted differently when exposed to the exact same virus strain (homotypic) and slightly different ones (nearly homotypic) as compared to exposure to significantly different strains (heterotypic).
• Horses exposed to the homotypic virus strain did not exhibit any clinical symptoms. This validated the efficacy of the vaccine.
• The results highlight the importance of vaccines being up-to-date with the virus strains currently prevalent in the horse population. In other words, the vaccine’s effectiveness against a particular strain of horse flu varies with the degree of similarity between the vaccinated and the challenging virus strain, emphasizing the need for vaccines to continually adapt to the evolving virus strains.