Equine Hepatitis Virus Infections in Horse Herds over Four Years

Abstract:

Background: Equine hepacivirus (EqHV) and equine parvovirus-hepatitis (EqPV-H) cause chronic and acute hepatitis in horses, respectively. Based on high global seroprevalence, horizontal transmission must occur. Insect vectoring is suspected for both viruses and nasal transmission of EqPV-H has been experimentally demonstrated.
Hypothesis/

Objectives: We hypothesized EqHV transmission is seasonal and EqPV-H is not. Our objective was to determine transmission rates, clearance rates, and seasonality of transmission.
Animals: Seven horse herds were enrolled, with 343 horses tested at least once and 144 horses tested over a year.

Methods: Prospective longitudinal cohort study. Paired serology using luciferase immunoprecipitation system and (RT)-qPCR for EqHV and EqPV-H was performed on quarterly serum from all horses and serum and plasma at 1 day, 1 and 2 months of age for mare-foal pairs.

Results: Within each year, EqHV prevalence was 2-8% persistently infected and 74-83% seropositive. Acute viremia was detected in 29 horses in June, September, and December. One plasma lot was EqHV RT-qPCR positive and the recipient foal became transiently infected. Within each year, EqPV-H prevalence was 28-57% seropositive all of which were consistently or intermittently qPCR positive. Acute viremia and seroconversion was observed in one adult. Plasma lots were frequently seropositive (9/24, 38%). Foal infections were significantly associated with EqPV-H seropositive plasma administration (10/28 vs. 1/19, p = 0.03).
Conclusions and clinical importance: Apparent seasonal transmission of EqHV could indicate insect-mediated transmission. Low transmission of EqPV-H in herds with only chronically infected adults prevented assessment of seasonality. USDA-licensed EqPV-H qPCR-negative, seropositive plasma might transmit EqPV-H.