EHV-1 and EHV-4 infection in vaccinated mares and their foals.

This research article presents a study conducted in a horse stud farm that revealed a continuous cycle of equine herpesvirus 1 and 4 (EHV-1 and EHV-4) infection in both vaccinated adult horses (mares) and their young, unvaccinated offspring (foals). Despite vaccination, there is an evidence of virus excretion and spread among the populations.

Methodology of the Research

• The study was an epidemiological research carried out on a Hunter Valley stud farm. This is a controlled environment that has a specific population of horses that can be monitored for certain conditions.
• For decades, the population of mares and foals in the study was unvaccinated. In 1997, a change was made and the adult horses began to receive routine vaccinations using an inactivated whole virus EHV-1 and EHV-4 vaccine.
• Research was conducted over a period of time, with nasal swab samples frequently taken from the mares and their foals for PCR testing. This assisted in identifying the presence and excretion of EHV-1 and EHV-4.
• A sero-epidemiological investigation was also carried out. This involves testing the blood of the animals for the presence of specific antibodies, indicating whether an infection has occurred.

Key Findings of the Research

• The PCR tests from the nasal swab samples revealed that both EHV-1 and EHV-4 were being excreted by the vaccinated mares and their unvaccinated, unweaned foals. This suggested that the viruses were still active within these populations despite the vaccination.
• The sero-epidemiological investigation further confirmed the presence of EHV-1 and EHV-4 infections, as specific antibodies were found in the blood of both mares and foals during the first 5 weeks of the foals’ lives.

Implications of the Research

• The study results demonstrate that even in vaccinated horse populations, EHV-1 and EHV-4 can still circulate. This is an important finding for equine herd health management, as it indicates potential gaps in immunization practices or vaccine efficacy.
• The research also confirms the continued cycle of EHV-1 and EHV-4 infection, underscoring the neccessity for continued vigilance in monitoring and controlling these diseases in equine populations.