Antemortem detection of latent infection with neuropathogenic strains of equine herpesvirus-1 in horses

Abstract

Objective - To evaluate a technique for identifying horses latently infected with neuropathogenic strains of equine herpesvirus-1 (EHV-1). Animals - 36 adult mares, 24 of which were experimentally infected as weanlings with neuropathogenic or nonneuropathogenic EHV-1. Procedures - Mandibular lymph node (MLN) tissue was obtained from each horse via biopsy during general anesthesia. Purified DNA from MLNs was tested for EHV-1 DNA by use of a magnetic bead, sequence-capture, nested PCR assay. For MLNs that contained EHV-1 DNA, the 256-bp DNA fragments amplified via sequence-capture nested PCR were sequenced to determine the nucleotide at the polymorphic site that determines pathotype (ie, neuropathotype [G2254] or non-neuropathotype [A2254]). Results - Latent viral DNA was detected in 26 of the 36 (72%) mares tested. Neuropathogenic and nonneuropathogenic EHV-1 genotypes were detected in the latently infected horses. In each mare previously infected with known EHV-1 pathotypes, the open reading frame 30 genotype of latent EHV-1 was identical to that of the strain that had been inoculated 4 to 5 years earlier. Latent viral DNA was detected in 10 of the 12 mares that were inoculated as weanlings with neuropathogenic strains of EHV-1. The detection rate of the sequence-capture PCR method for EHV-1 latency was double that of conventional nested or real-time PCR assays performed on the same MLN DNA preparations. Conclusions and clinical relevance - The magnetic bead, sequence-capture, nested PCR technique enabled low-threshold detection of DNA from latent neuropathogenic strains of EHV-1 in MLN specimens from live horses. The technique may be used to screen horses for latent neuropathogenic EHV-1 infection.