Investigation of the EHV-1 Genotype (N, D, and H) in Swabs Collected From Equids With Respiratory and Neurological Disease and Abortion From the United States (2019-2022).

Contemporary data on equine herpesvirus-1 (EHV-1) genotype (non-neuropathogenic or N, neuropathogenic or D and new variant or H) in clinically diseased equids is important in order to determine the frequency of these genotypes and their association with disease expression. A total of 297 EHV-1 qPCR-positive swabs collected from 2019 to 2022 from horses with respiratory disease (EHV-1), neurological disease (equine herpesvirus-1 myeloencephalopathy [EHM]) and abortion were tested for the three different EHV-1 genotypes (N, D and H) using qPCR allelic discrimination assays. All submissions originated from the United States and included 257 EHV-1 cases, 35 EHM cases and 5 cases of abortion. EHV-1 qPCR-positive cases were predominantly seen during winter and spring. N was the predominant genotype detected in EHV-1 cases (87.5%), EHM cases (74.3%) and abortions (80%). D was detected less frequently in EHV-1 cases (9.3%) and EHM cases (25.7%), while H was only detected in EHV-1 cases (3.1%). While the N genotype has remained the predominant genotype affecting horses with respiratory disease and abortion, it has also become a leading genotype in cases of EHM, when compared to historical data. The new H genotype, first reported in the United States in 2021, has remained confined to a cluster of geographically and temporally related outbreaks and the data showed no emerging spread of H since it was first reported. While the monitoring of EHV-1 genotypes is important from a diagnostic and epidemiological standpoint, it may also help establish medical interventions and preventive protocols to reduce the risk of severe complications associated with EHV-1 infection.