A single mutation in the genome of equine herpesvirus-1 (EHV-1) was “necessary and sufficient” to cause neurologic disease in horses in a new study, reported Cornell University researchers.

All strains of EHV-1 can cause respiratory disease and abortion, but only a subset of EHV-1 strains can cause neurologic disease said Nikolaus Osterrieder, DVM, DVM Habilitation (equivalent to PhD), and colleagues. It has previously been suggested that some strains of EHV-1 have a single genetic mutation in the gene that encodes the enzyme called DNA polymerase. This genetic mutation results in the enzyme sporting the amino acid aspartic acid at position 752 of the enzyme instead of an asparagine amino acid residue.

In light of this single, seemingly relatively innocuous substitution, the researchers wanted to determine whether the mutation was “not only necessary but also sufficient” to cause neurologic disease.

They studied this by taking a nonneurovirulent strain of EHV-1 obtained from an aborted equine fetus and inserting the single point mutation into its genome. Six horses were inoculated with the mutated virus and three horses were inoculated with the native, nonneurovirulent virus