Investigation of Neurologic Equine Herpes Virus 1 Epidemiology From 1984-2007
ACVIM 2008
G.A. Perkins; L.B. Goodman; K. Tsujimura; G.R. Van de Walle; S.G. Kim; E. Dubovi; N. Osterrieder
Cornell University, College of Veterinary Medicine
Ithaca, NY, USA

A single nucleotide polymorphism in the equine herpesvirus 1 (EHV-1) DNA polymerase gene (ORF30 A2254 to G) is causally associated with clinical signs of equine herpes myeloencephalopathy (EHM) (PLoS Pathog 2007;3:e160). The purpose of our study was to investigate the association of this genetic marker with EHV-1 disease prevalence in field isolates from North America over the past twenty-four years.

EHV-1 isolates cultured at the Cornell University Animal Health Diagnostic Laboratory from 1984-2007 were retrieved along with their clinical histories. The DNA was prepared and allelic discrimination performed using real-time PCR as described by G. Allen (J Vet Diagn Invest 2007;19:69-72) and confirmed by partially sequencing the ORF30 region. The odds ratio was computed by logistic regression.

There were a total of 179 EHV-1 isolates. About 90% of isolates were from New York (117), Pennsylvania (27) and Virginia (13) and the rest were from 9 other states. The majority of samples were from fetal tissue, placenta and blood. Three isolates were from fatal disease in other species (alpaca, zebra, and fallow deer) and had the mutant ORF30 G2254 detected by PCR (3/3) and by sequencing (2/3). These isolates were not included in further analysis. PCR and sequencing were in 100% agreement. There were 11% (19/176) isolates that were defined as the mutant ORF30 G2254 by PCR.

Number of EHV-1 Isolates categorized by the ORF30 genotype and clinical sign.





ORF30 G2254




ORF30 A2254








The odds of having neurologic disease with the ORF30 G2254 genotype versus the ORF30 A2254 are 162 times greater (95% confidence interval 35-742). Combining our data with the results reported by Nugent et al. (J Virol 2006;80:4047-4060) gives an odds ratio of 490. Despite this strong statistical significance, 24% (5/21) of horses with neurologic disease in our study population had the "non-neurologic" form (ORF30 A2254), suggesting that other factors may also contribute to the onset of EHM.

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Gillian Perkins

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