Isolation and Identification of Emerging Equine Encephalosis Virus Serotype 6 in Israel, 2023

Equine encephalosis (EE) is an arthropod-borne viral disease resembling a mild form of African horse sickness disease, which affects all species of equids. Previously, only EEV serotype 4 (EEV-4) caused sporadic outbreaks of the disease in Israel. In the summer of 2023, EE was clinically diagnosed in horses and donkeys in Israel. For laboratory confirmation, tissue cultures were inoculated with whole-blood samples obtained from sick animals. Five EEV isolates were successfully recovered in tissue and confirmed by conventional RT-PCR and Sanger sequencing of several viral genes. BLAST analysis of genome segment 2 revealed that the isolates belonged to serotype 6. Full-genome sequencing of one representative strain and subsequent phylogenetic analysis demonstrated a close relationship to South African and Indian EEV strains, suggesting possible epidemiological links that warrant further investigation. This observation can indirectly point to a broader geographic circulation of EEV than was previously thought.