Equine herpesvirus 1 (EHV-1) nucleotide polymorphism determination using formalin fixed tissues in EHV-1 induced abortions and myelopathies with real-time PCR and pyrosequencing

Equine herpesvirus-1 (EHV-1) strains with a single point mutation at the 2254 nucleotide position with a G₂₂₅₄ constitution within the DNA polymerase gene are associated strongly with equine myeloencephalopathies. Infections with non-neuropathogenic EHV-1 strains without the G₂₂₅₄ nucleotide but with an A₂₂₅₄ nucleotide are associated less frequently with equine neurologic disease. A retrospective study utilizing DNA extracted from formalin fixed paraffin embedded tissues was conducted with real time PCR and pyrosequencing, to determine the infecting EHV-1 strains. Infection with EHV-1 A₂₂₅₄ and or G₂₂₅₄ strain was detected with real time PCR, and was confirmed with a rapid pyrosequencing technique. Pyrosequencing was useful in at least 2 cases where real time PCR was equivocal in determining the infecting EHV-1 strain type. The strain with G₂₂₅₄ mutation was detected in 9.4% of 21 studied abortion cases, and in 86.6% of 15 neurologic cases.