Frequency of latent equine herpesvirus type-1 infection among a sample of horses in the central North Island of New Zealand.

This research paper is about a study investigating the rate of equine herpesvirus type-1 (EHV-1) infection among horses in the central North Island of New Zealand and determining the prevalence of the D genotype of the virus.

Study Design and Sample Collection

• The research was conducted on tissues taken from 63 horses, that were euthanized due to various unrelated reasons.
• Specimens of retropharyngeal lymph nodes (RLN) and submandibular lymph nodes (SLN) were retrieved for analysis. The sample collection happened between March and November 2015.
• The DNA extracted from these tissues underwent enrichment specifically targeting EHV-1 sequences.

Analysis of EHV-1

• The enrichment process involved a hybridization step with a biotin-labelled EHV-1 specific probe. This allows the EHV-1 sequences to be pulled out from the pool of DNA with the help of streptavidin-coated magnetic beads, hence “enriching” the sample with sequenced EHV-1 DNA.
• These enriched samples were further tested for the presence of EHV-1 with a highly sensitive method – nested quantitative real-time PCR.

Genotype Identification

• The study also aimed to identify the genotypes of the observed viruses. For this purpose, the amplified EHV-1 DNA bits (amplicons) were sequenced.
• The sequenced EHV-1 amplicons demonstrated the N genotype, while no traces of the D genotype were noted.

Results and Implications

• Of the total samples, about 10% (6/63) showed the presence of EHV-1 DNA in RLN samples, with a subset of these (3/6) also testing positive in SLN samples.
• The study points to the fact that EHV-1 is actively circulating among horses in New Zealand, though the absence of the D genotype suggests its infrequency in this region.
• It’s important to note that a negative result from sampling SLNs does not necessarily indicate the absence of EHV-1, especially as the virus can lie dormant in other parts of the body that are less accessible to testing. Therefore, RLNs provide a better sample source in cases where horses are recently euthanized.
• The research indicates that the actual rate of latent EHV-1 infection might be higher, due to the limitations of the assay’s sensitivity or because of the restricted sampling locations.