Sero-epidemiological study on equine influenza in Japan.

This research article discusses a study on the incidence of equine influenza (EI) in Japan, conducted on horse serum samples collected over seven years prior to the country’s first EI outbreak in 1971. The study did not find EI antibodies in any of the native horses but found a significant presence in imported horses.

Objective and Methodology

• The main purpose of this study was to assess the sero-epidemiological status of Equine Influenza (EI) in Japan during the seven years preceding the first EI outbreak in 1971.
• The research focused on evaluating antibodies against two strains of the EI virus; A/Equi-1/Prague/56 (equi-1) and A/Equi-2/Miami/63 (equi-2).
• The researchers used hemagglutination inhibition (HI) and complement fixation (CF) tests against viral (V) antigen to detect these antibodies.
• The sample pool included sera from 452 native horses and 80 imported horses.

Study Findings

• None of the 452 native horses had antibodies against the equi-1 and equi-2 strains of the EI virus.
• However, in the case of the imported horses, 60% had HI titers of 1:8 or higher against equi-1 and 28.8% against equi-2, indicating the presence of antibodies against these EI strains.
• In the CF-V test, 42.6% and 42.9% of the imported horses showed titers of 1:4 or higher against equi-1 and equi-2 antigens, respectively.
• Notably, all sera from both native and imported horses were negative against soluble human influenza antigen in CF tests, establishing that these antibodies are specifically related to EI.

Epidemiological Analysis

• The researchers performed an epidemiological analysis to understand the relationship between the history and the presence of EI antibodies in individual imported horses.
• Though the results from this analysis are not provided in the abstract, this component of the study likely contributed to understanding how EI came to Japan and shed light on potential measures to prevent future outbreaks.