Seroprevalence of equine herpesvirus 1 in mares and foals on a large Hunter Valley stud farm in years pre- and postvaccination.

The study investigates the prevalence of equine herpesvirus 1 (EHV-1) antibodies in mares and foals on a horse farm before and after the introduction of a vaccine. It finds that while the prevalence in mares didn’t change significantly, the presence of virus antibodies in foals decreased after vaccination.

Study methods

• The research was conducted on a large Hunter Valley Thoroughbred stud farm in New South Wales. It involved cross-sectional serological surveys that were carried out in February 1995, 2000 and 2001 to understand the prevalence of EHV-1 antibody-positive mares and foals.
• Different sets of mares and their foals were sampled for each study year, with 229 pairs in 1995, 236 in 2000, and 264 pairs in 2001. However, there were 50 mares who were sampled in both the 1995 and 2000 studies.
• Blood samples were collected from each mare and foal at the beginning of each study year. The samples were repeatedly tested using an antibody-detection ELISA (enzyme-linked immunosorbent assay) which is a method specific for determining EHV-1 and EHV-4 antibodies.

Result findings

• The study found that there was no significant difference in the prevalence of EHV-1 antibody-positive mares in 2000 compared to 1995. However, the prevalence of antibody-positive foals was significantly lower in 2000 than in 1995.
• In the 2001 survey, the antibody prevalence in mares increased from 2000, but it was not statistically different from the 1995 levels. The prevalence in foals did not significantly vary from levels observed in 1995 or 2000. But when the three studies were compared, researchers noted significant variations in the prevalence of EHV-1 positive foals, mainly due to the difference between data from 1995 and 2000.

Conclusions

• According to the study’s conclusions, mares are the source of the virus from which foals get infected early in their life. After the 2001 data analysis, it was found that the difference in the prevalence of EHV-1 antibody-positive foals between 1995 and 2000 was likely to be influenced by seasonal, nutritional and management factors, rather than the effect of vaccination. This suggests that while vaccination might have contributed to reducing the EHV-1 prevalence in foals, other factors might have also played an essential role and hence need to be considered in managing the prevalence of this virus in horse populations.