Neuropathogenic and non-neuropathogenic variants of equine herpesvirus 1 in France

Equine herpesvirus 1 (EHV-1) is a common pathogen of the horse which may induce mild respiratory distress, abortion, neonatal death and neurological disease. A single nucleotide polymorphism in the EHV-1 DNA polymerase (ORF30 A 2254 to G 2254) has been associated with clinical signs of Equine herpes myeloencephalopathy (EHM). The aim of this work was to analyze the ORF30 genomic region among a panel of EHV-1 DNA extract in order to estimate the prevalence of the EHV-1 neuropathogenic genotype in France. Samples coming from cases associated with EHM, horses with respiratory symptoms and aborted mares, each obtained between 2002 and 2009, were investigated. DNA was directly extracted from biological samples and allelic discrimination was performed using real-time PCR. Thirty of the 125 analysed horses (24%) presented the G 2254 genotype of ORF 30. Among them, 7/16 were provided by EHM cases, 1/24 by respiratory cases and 22/85 by abortion cases. Concerning EHM, the 7 G 2254 genotype of ORF30 were all isolated in 2009 during two outbreaks where mortality was observed. Regarding the 22 G 2254 genotype of ORF 30, 17 were identified in foetuses on which EHV-1 was detected by PCR, without any certainty of viral implication in the abortion. These findings clearly suggest that other factors need to be considered for a better understanding of the impact of DNA polymerase genotype upon EHV-1 neuropathogenic phenotype.