Sero-epizootiological study of racehorses with pyrexia in the training centers of the Japan Racing Association.

This study investigates the causes of fever in racehorses at two Japanese training centers over a six-year period, finding that a significant number of fevers were due to specific viruses such as equine herpesvirus type 1, equine rhinovirus type 1, rotavirus and equine adenovirus, each exhibiting unique seasonal spread patterns.

Study Overview

In an effort to shed light on the causes of fever in racehorses, a sero-epizootiological study was run from 1980 to 1985. This study focused on two training centers run by the Japan Racing Association. Each center trained between 1,200 and 2,100 racehorses.

Data Collection

• Throughout these six years, 3,849 horses were identified to have fever.
• Out of these, paired serum samples were collected from 2,852 horses and tested for several specific viruses.
• The viruses tested were: equine herpesvirus type 1 (EHV-1), equine rhinovirus type 1 (ERhV-1), rotavirus and equine adenovirus (EAdV).

Results

• Of the tested horses, 669 (or 23.5%) were found to have one or more of these viruses.
• The breakdown of viral presence among these 669 horses was: 73.4% with EHV-1, 13.6% with ERhV-1, 9.6% with rotavirus and 3.4% with EAdV.

Seasonal Trends

• The researchers also found seasonal trends in the spread of these viruses. EHV-1 and rotavirus were more prevalent in the winter and early spring.
• ERhV-1 was found not just in cold seasons but also during seasonal changes, notably in early spring and early autumn.

Age Trends

• In horses showing seroconversion to EHV-1, the percentage of 3 years old horses was double compared to those displaying seroconversion to other viruses.
• All of the horses showing seroconversion to ERhV-1 and EAdV were under 4 years and 3 years respectively.
• The average age of horses showing seroconversion to these viruses were: 2.96 years for EHV-1, 2.73 year for rotavirus, 2.44 years for ERhV-1 and 2.25 years for EAdV.