Virological and serological investigation of Equid herpesvirus 1 infection in New Zealand.

The study focuses on examining the prevalence and types of Equid Herpesvirus 1 (EHV-1), a disease that can cause various symptoms or even be asymptomatic, in a selected group of New Zealand horses. It also sets out to determine how effective serology is in detecting latent infections of EHV-1 in these horses.

Research Objectives and Methodology

• Two key objectives drove this study. Firstly, to estimate the prevalence of EHV-1 infection within a chosen population of New Zealand horses, including differentiation between genotypes with aspartic acid (D) and asparagine (N) at position 752 of the DNA polymerase sequence. Secondly, to determine the predictive value of serology for detection of horses infected with the virus but not showing symptoms.
• The researchers obtained samples from 52 slaughtered horses. Their retropharyngeal lymph nodes (RLN) and trigeminal ganglia (TG) were dissected and tested for EHV-1 DNA. The testing process involved using a nested PCR after enriching the samples with magnetic bead, sequence-capture.
• Sera from the horses were also tested for EHV-1 antibodies using a particular ELISA that targets glycoprotein G, unique to the herpesvirus.

Research Findings

• The research findings showed that 17 out of 52 horses tested positive for EHV-1 DNA. With the exception of one, all positive PCR results came from RLN samples. 15 of the EHV-1 positive horses were found to carry EHV-1 of the N752 genotype. One of these horses was discovered to also be infected with the D752 genotype of EHV-1.
• This data represents the first detection of EHV-1 with the D752 variant in New Zealand. Interestingly, the researchers suggest that this “neurovirulent” form of EHV-1 had been present in New Zealand for at least two years before the country’s first reported outbreak of Equine Herpes Myeloencephalopathy (EHM).
• All horses sampled had antibodies for EHV-4. Meanwhile, 11 out of 52 tested positive for EHV-1 antibodies.
• The researchers concluded that the concordance between the results of the PCR and EHV-1 serology was “fair” (Kappa 0.259, 95% CI: -0.022-0.539). This outcome is seen as a reflection of low levels of both EHV-1 antibody in sera and EHV-1 DNA in the tissues tested.

Implications of the Research

• The findings of this study can have significant implications for managing EHV-1 in horses. Knowledge about the types and prevalence of this virus in the New Zealand horse population can inform more effective control and treatment strategies.
• The effectiveness of serological tests in detecting latent infections also has significant implications for disease management. It can be used as a tool for screening, diagnosis, or monitoring of EHV-1 infection in the horse population.