Antibody responses of Japanese horses to influenza viruses in the past few years.

This research paper examines the antibody responses of Japanese horses to various strains of equine influenza virus between 1988 and 1990.

Study Objective and Method

• The research aimed at analyzing the antibody responses of 305 Japanese horses, from the Hidaka district of Hokkaido, towards the equine influenza (EI) virus strains – A/equine/Newmarket/1/77 (H7N7), A/equine/Tokyo/2/71 (H3N8), and A/equine/Kentucky/1/81 (H3N8, Kentucky).
• This was conducted by testing the horse sera collected between 1988 and 1990 for the presence of hemagglutination-inhibition (HI) antibodies to these strains.
• The sample set included sera from vaccinated and unvaccinated horses, aged between 2 and 23 years, in order to identify patterns and differences in antibody presence.

Findings and Significance

• It was discovered that hardly any of the 45 two-year-old horse sera samples, collected before vaccination, contained antibodies to the three EI virus strains observed.
• However, a substantial number of the 51 horses, which were vaccinated with inactivated EI virus, showed HI antibodies to the same virus strains – ranging from 37 to 88 percent of cases.
• Interestingly, it was found that the number of positive reactors (horses with detectable response to the virus) decreased as the age of the horses increased. More specifically, no antibody responses to these strains were found in the 60 horse samples of over 9 years old, except for cases where low titer HI antibody to the Kentucky strain was found.
• The researchers note that the Kentucky strain has been increasingly prevalent among horse populations worldwide, thus low titer antibody to this strain may still exist among older equine populations.
• A complement-fixing test was also conducted, discovering antibodies to the soluble antigen of type A influenza virus in the sera collected from horses exposed to an outbreak of EI virus infection – but not in the sera from the vaccinated horses examined
• The findings are significant as they shed light on the effectiveness of current vaccinations for equine influenza and present an age-related pattern in the horses’ antibody response.