Viremia and nasal shedding for the diagnosis of equine herpesvirus‐1 infection in domesticated horses

Background Equine herpesvirus type 1 (EHV‐1) infection is associated with upper respiratory disease, EHM, abortions, and neonatal death. Research Questions Are nasal secretions a more sensitive biological sample compared to blood for the detection of EHV‐1 infection? How long is EHV‐1 detectable after primary infection by PCR? Methods MedLine and Web of Science searches identified original peer‐reviewed reports evaluating nasal shedding and viremia using virus isolation methods or PCR published in English before October 9, 2023. Results Sixty experimental and 20 observational studies met inclusion criteria. EHV‐1 detection frequency by qPCR in nasal secretions and blood from naturally‐infected horses with fever and respiratory signs were 15% and 9%, respectively; qPCR detection rates in nasal secretions and blood from horses with suspected EHM were 94% and 70%, respectively. In experimental studies the sensitivity of qPCR matched or exceeded that seen for virus isolation from either nasal secretions or blood. Detection of nasal shedding typically occurred within 2 days after EHV‐1 inoculation with a detection period of 3 to 7 days. Viremia lasted 2 to 7 days and was usually detected ≥1 days after positive identification of EHV‐1 in nasal secretions. Nasal shedding and viremia decreased over time and remained detectable in some horses for several weeks after inoculation. Conclusions and Clinical Importance Under experimental conditions, blood and nasal secretions have similar sensitivity for the detection of EHV‐1 when horses are sampled on multiple consecutive days. In contrast, in observational studies detection of EHV‐1 in nasal secretions was consistently more successful.