Detection and Characterization of Equine Herpesvirus-1 Strains in Submandibular Lymph Nodes and Trigeminal Ganglia From Horses Using Real-Time PCR
ACVIM 2008
N. Pusterla; S. Mapes
School of Veterinary Medicine, University of California
Davis, CA, USA

Equine herpesvirus-1 (EHV-1) is an important, ubiquitous equine viral pathogen that causes significant economic losses to the equine industry and produces well-documented syndromes of respiratory disease, abortion, neonatal foal death and myeloencephalopathy. Latency and reactivation are key features of the biology and epidemiology of EHV-1. Functional latency of EHV-1 is routinely established in circulating and lymph node T lymphocytes and in neurons within the trigeminal ganglia. The aim of this study was to detect and to characterize the strains of EHV-1 from submandibular lymph nodes and trigeminal ganglia collected from horses using real-time PCR.

One hundred and eleven horses, two mules and one donkey euthanized for reasons other than acute respiratory or neurologic diseases were included in this study. There were 42 mares, 54 geldings, 7 stallions and 11 foals with ages ranging from 2 months to 39 years (mean 14.3 years). Tissue samples including a piece of submandibular lymph node, and both trigeminal ganglia were collected during post-mortem examination in all animals, while uncoagulated blood samples and nasal swabs were collected from 43 animals prior to euthanasia. All samples were processed for nucleic acid purification within 24 hours of collection and tested for EHV-1 using real-time PCR assays targeting the glycoprotein B (gB) gene and the polymerase (ORF 30) gene. The latter assay allowed the characterization of EHV-1 into neuropathogenic and non-neuropathogenic strains. In order to detect as few as one target gene (gB and ORF 30), each purified DNA sample underwent a precipitation and pre-amplification step.

None of the 43 uncoagulated blood samples and nasal swabs and none of the 114 submandibular lymph nodes tested PCR positive for the gB gene and the ORF 30 gene of EHV-1. A total of 15 trigeminal ganglia collected from 9 horses tested PCR positive for the gB gene of EHV-1. Six and 3 horses tested PCR positive for the gB gene of EHV-1 in both and only one trigeminal ganglia, respectively. Eight trigeminal ganglia harbored non-neuropathogenic EHV-1 strains, while two trigeminal ganglia tested PCR positive for the neuropathogenic ORF 30 gene. Five trigeminal ganglia tested PCR positive for both the neuropathogenic and the non-neuropathogenic ORF 30 gene of EHV-1.

In conclusion, 7.9% of study horses had molecular evidence of EHV-1 in their trigeminal ganglia. The results provide evidence that trigeminal ganglia serve as a latency site of EHV-1. This was in sharp contrast to the submandibular lymph nodes, since none of them tested PCR positive for EHV-1. Non-neuropathogenic strains of EHV-1 were more commonly detected than neuropathogenic strains in the trigeminal ganglia of the study horses.

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Nicola Pusterla

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