Incidence of equine herpesvirus 1 infection in thoroughbred weanlings on two stud farms.

This research article examines the incidence of Equine Herpesvirus 1 (EHV-1) infection in thoroughbred weanling horses on two stud farms. It presents the data gathered from testing serum samples, aiming to develop more effective strategies for managing and preventing EHV-1 within horse herds.

Introduction and Background

• The paper begins by acknowledging that the epidemiology of EHV-1 – a virus first identified as a cause of equine abortion in 1932 – is not completely understood.
• The study aims to fill gaps in the research, notably with regard to the assertion that weanlings, young horses aged between six months and a year, might be a primary reservoir for the virus.
• Earlier studies referenced in this article have associated EHV-1 primarily with respiratory disease in weanlings and the closely related EHV-4 rather than EHV-1 was found to cause the majority of these infections.

Research Method

• Serum samples were collected from 200 thoroughbred foals on two adjacent stud farms in New South Wales, Australia.
• The samples were collected at 2-week intervals from the weanlings’ approximate time of weaning until June 1995.
• Each sample was tested for EHV-1 using a type-specific ELISA (enzyme-linked immunosorbent assay) test, which has been previously proven to be both sensitive and specific.
• A serum sample was considered positive for EHV-1 if the ELISA absorbance was greater than 0.129, a cut-off value determined in a previous study.

Identifying EHV-1 Infection Cases

• The foals showing serological evidence of EHV-1 infection were categorized as “existing cases” or “new cases”.
• “Existing cases” were defined as any foal which had EHV-1 antibody present in at least the first two periods sampled after recruitment into the study.
• “New cases” were defined as any foal which was initially negative for EHV-1 antibody in at least one sample period, but tested positive subsequently in at least three consecutive sample periods.
• No foal seroconverted, or produced an antibody response to EHV-1, more than once during the study.

Results

• From the 200 initial foals, 28 were excluded from the results due to insufficient sample collection. Therefore, 172 foals were considered “at risk” for the study.
• Seventeen new cases were identified from these 172 foals between February and June 1995, contributing an incidence density rate (actual rate) of 12.4 new cases per 1000 foal weeks at risk.
• There was an observed increase in new cases from the second period to the fourth, and a decline afterwards, indicating the changing risk factor for EHV-1 infection amongst the foal population over time.

Conclusion

• The in-depth studies like these give insights in understanding the disease dynamics and thus are critical in establishing management strategies, including vaccination plans to control infections in the at-risk population.