E26 - Characteristics of Nasal Shedding and Viremia Following Experimental Infection with Equid Alphaherpesvirus 1 in Horses

Abstract:

Background: Equid alphaherpesvirus 1 (EHV-1) is a cause of respiratory disease, abortion, and neurologic disease (equine herpes myeloencephalopathy or EHM) in horses. A cell-associated viremia in PBMC is linked to the development of EHM.

Hypothesis: Different infectious doses affect nasal shedding, viremia, and virus neutralization (VN) titers in horses.

Animals: Ten healthy EHV-1–naive horses.

Methods: In this randomized controlled field trial, horses received ‘low’ (1×104 PFU; n=4), ‘medium’ (1×106 PFU; n=4), or ‘high’ (standard) (5×10⁷ PFU; n=2) inoculum EHV-1 (strain Ab4) via nasopharyngeal instillation. Pre and post infection nasal swabs, whole and EDTA blood samples were collected for 21 days and analyzed by quantitative PCR (nasal swabs and viremia) and virus neutralization assay. Data was analyzed using GraphPad Prism, and results were reported with 95% confidence interval.

Results: All horses shed EHV-1 for 14 to 16 days following the infection, with significant variation within the ‘low’ and ‘medium’ groups. ‘High’ dose horses had an exponential peak at the onset of nasal shedding. All horses developed viremia for 3-5 days with onset on days 4 or 5. Differences in magnitude and duration of viremia were not observed between groups. Horses seroconverted similarly following infection. One horse in the ‘high’ dose group developed EHM.

Conclusions: EHV-1 infectious dose has an effect on viral shedding patterns. Viremia seemed not to be affected by these infectious doses. Other qualitative aspects of viremia need further investigation.