Comparison of protective efficacies between intranasal and intramuscular vaccination of horses with a modified live equine herpesvirus type-1 vaccine.

The study assesses the effectiveness of Intranasal (IN) and intramuscular (IM) vaccination methods of horses using a modified live equine herpesvirus type-1 (EHV-1) vaccine. Both methods resulted in increased immunity; however, differences were observed in the induced types of immune responses and disease prevention after exposure to the virus.

Study Design and Execution

• The participants for this research were horses. The horses were randomly grouped into three: the intranasal (IN) vaccinated group, intramuscular (IM) vaccinated group, and the placebo (PBO) group. Each group consisted of five horses.
• The IN and IM groups were vaccinated with a modified live equine herpesvirus type-1 (EHV-1) vaccine, while the PBO group was presumably left unvaccinated for comparison.
• After vaccination, the immune responses of the horses were monitored and compared. This was done by measuring various indicators: serum virus-neutralizing titers, levels of IgGa and IgGb antibodies in the blood, and levels of IgA antibodies in nasal secretions.
• The horses were then exposed to the EHV-1 virus, to evaluate the protective effect of the different vaccination methods.

Findings

• Both IN and IM vaccinated groups had significant increases in serum virus-neutralizing titers and increased levels of IgGa and IgGb antibodies after vaccination.
• The IN group also exhibited significantly increased levels of IgA antibodies in nasal secretions after vaccination. In contrast, the IM group’s response was dominated by bloodstream antibodies (IgGa and IgGb subclasses).
• Following exposure to the virus, fewer horses in the vaccinated groups (none in IN and one in IM) developed fever compared to the Placebo group (three out of five).
• Both the IN and IM groups had significantly lower instances of virus shedding than the PBO group. Virus shedding refers to the release of virus progeny following successful reproduction in the host cells – a lower rate means the virus is less likely to spread.
• Despite these results, there were no significant differences between the groups in daily numbers of viremic (presence of viruses in the blood) horses.

Conclusion

• Notably, two horses in the IM group had no instances of virus shedding or viremia, whereas all horses in the other groups did. This suggests that the IM vaccination, although inducing a slightly different response, might have led to better results in these particular instances.
• Both IN and IM vaccinations induced systemic and mucosal immunity, suppressing virus replication in the nasal mucosa. They partially protected the horses from fever, especially early in the infection.
• The study demonstrated that a mucosal antibody response could be induced not just by intranasal vaccination but also by intramuscular vaccination.