Investigation of the molecular detection of vaccine-derived equine herpesvirus type 1 in blood and nasal secretions from horses following intramuscular vaccination.

The study investigates the potential of detecting equine herpesvirus type 1 (EHV-1) in blood and nasal secretions of horses after they’ve been vaccinated with a killed or live-modified version of the virus. The researchers found no instances of the virus being detected in this way, revealing that vaccination doesn’t regularly lead to a false positive result for EHV-1 in healthy horses.

About the Study

• The aim of this research was to study if intramuscular vaccination of healthy adult horses with a killed or a modified live equine herpesvirus type 1 (EHV-1) vaccine could lead to positive PCR results in blood or nasal secretions.
• Four horses each received either a single killed vaccine or a modified-live vaccine delivered intramuscularly. There were control groups consisting of local and distant non-vaccinated horses.
• All the horses were kept under observation for any clinical abnormalities throughout the study period.
• Blood and nasal swabs were collected twice before vaccination, then weekly for four weeks post-vaccination. The samples went through PCR testing at two independent laboratories using different PCR methodologies.

Findings of the Study

• The two vaccine strains tested positive in both EHV-1 PCR assays. However, the nasopharyngeal swabs and whole blood taken from both vaccinated and control horses tested negative for EHV-1 throughout the entire study period.
• Through serum neutralization testing, a 2- to 4-fold increase in antibody titers was observed in all vaccinated horses, while titers in control horses remained largely unchanged.
• The researchers hypothesized that using already seropositive horses for immunization and a sampling frequency of 7 days could have hindered the occasional molecular detection of the vaccine virus in whole blood and nasal secretions.

Conclusion of the Study

• The study concluded that the detection of EHV-1 DNA by PCR in vaccinated and unvaccinated healthy horses is not a common occurrence.
• This suggests that vaccination does not often lead to a false positive result for EHV-1 in healthy horses, which is important for the effective management of the disease.