Serological responses and clinical outcome after vaccination of mares and foals with equine herpesvirus type 1 and 4 (EHV-1 and EHV-4) vaccines.

This study compares the effectiveness of two commercially available vaccines against equine herpesvirus type 1 and type 4 (EHV-1 and EHV-4) in preventing disease in horses. It found there were no significant differences between the two vaccines in terms of inducing immune response, but higher responses were seen with one of the vaccines at all times measured, and there were fewer cases of disease among the horses who received this vaccine.

Research Context

• This research is based on the premise that EHV-1 and EHV-4 cause significant disease in horses worldwide. These diseases can lead to severe clinical outcomes including respiratory disease and abortion.
• While EHV-1 is responsible for the majority of infections, both types of herpesvirus can cause significant morbidity and are controlled through hygienic measures and vaccination programs.

Study Design and Outcomes

• This study compared two commercially available vaccines, one combination of inactivated EHV-1 and EHV-4, and the other a modified live virus (MLV) vaccine.
• During the course of the study, vaccines were administered to horses at a large stud farm. The MLV vaccine was given twice during pregnancy (in the 5th and 8th month) and the inactivated vaccine was given three times (in the 5th, 7th and 9th month).
• Serum samples were analyzed from a randomly selected group of vaccinated mares. There was no significant difference between the two vaccine groups in terms of the magnitude or duration of the immune response as assessed through serum neutralization assays and EHV-1-specific IgG isotype testing. The MLV vaccine, however, did show higher neutralizing responses at all sampling points.
• Among all vaccinated mares, a total of 55 abortions were reported, out of which 9 were attributed to EHV-1. Among these, 7 abortions were in mares vaccinated with the inactivated vaccine, while 2 were in the MLV vaccine group.

Findings and conclusions

• The study found that the maternally derived antibody’s half-life is less than 4 weeks, indicated by the dramatic drop of serum neutralizing titers in the foals of vaccinated mares.
• Consequently, this would infer that both vaccines had similar efficacy in inducing immune responses; however, the MLV vaccine resulted in fewer cases of diseases, suggesting it may offer superior protection.