Vaccination of foals with a modified live, equid herpesvirus-1 gM deletion mutant (RacHΔgM) confers partial protection against infection.

The researchers conducted a study using a modified live virus vaccine in foals to stimulate a stronger immune response to Equid herpesvirus-1 (EHV-1), a virus that can cause serious illness in horses. The vaccine didn’t completely prevent infection but resulted in less severe symptoms and less virus replication.

Research Context and Objectives

• This study was conducted in response to previous vaccines’ inability to provide full clinical or virological protection against the Equid herpesvirus-1 (EHV-1). EHV-1 is responsible for respiratory and neurological diseases, as well as late gestation abortion in pregnant mares.
• The primary objective was to investigate if a modified live virus (MLV) vaccine could stimulate a more effective immune response against the virus. For this, a glycoprotein M (gM) deletion mutant of EHV-1, known as RacHdeltagM, was used in the vaccine.

Research Methods

• A longitudinal, prospective, experimental study design was employed, involving two groups of weaned foals (six in each group).
• The foals received two intranasal and intramuscular vaccinations six weeks apart, then were exposed to the EHV-1 virus four weeks following the second vaccination.
• The researchers closely observed and recorded clinical signs and virological replication in both the vaccinated and control group.

Research Findings

• The vaccine didn’t cause any adverse events, but it did result in higher levels of complement fixing and virus neutralizing antibodies as compared to the control group.
• However, there were no significant differences in virus-specific nasopharyngeal antibody levels and cytotoxic T lymphocyte responses between the vaccinated and control groups.
• Post exposure, the immune responses in the vaccinated foals were associated with less severe clinical signs and less viral replication, as well as a reduction in pyrexia, nasopharyngeal shedding, and cell-associated viraemia durations.

Research Conclusions and Implications

• Based on the observed results, the researchers concluded that the RacHΔgM MLV vaccine primed EHV-1-specific humoral immune responses in weaned foals.
• However, the vaccine didn’t provide complete virological protection against EHV-1, indicating that more research in this area is necessary.