Natural Recombinant between Equine Herpesviruses 1 and 4 in the ICP4 Gene

Equine herpesvirus 1 (EHV‐1) is a pathogen causing rhinopneumonia in young horses, abortion in mares, and myeloencephalitis in adult horses. Two types, EHV‐1 P and EHV‐1 B, have recently been dominant among 16 electropherotypes. EHV‐1 P and EHV‐1 B viruses were compared by long and accurate polymerase chain reaction (LA‐PCR) and restriction fragment length polymorphism (RFLP) analysis. Differences in restriction sites were found to be focused in ORF64, which encodes the infected cell protein 4 (ICP4), and downstream of the ICP4 gene. The 3′‐end and downstream of ICP4 gene of EHV‐1 B were found to be replaced by the corresponding region of EHV‐4, indicating that EHV‐1 B is a naturally occurring recombinant virus between progenitors of EHV‐1 P and EHV‐4. This is the first report showing a natural interspecies recombinant in alphaherpesviruses.