The effect of siRNA treatment on experimental equine herpesvirus type 1 (EHV-1) infection in horses.

Available vaccines fail to induce lasting and protective immunity to equine herpesvirus 1 (EHV-1) associated diseases. RNA interference is a novel approach showing promise for therapeutic use in outbreak situations. This study examined the effect of small interfering RNA (siRNA) on clinical signs as well as the presence of live virus and viral DNA in nasal secretions and peripheral blood mononuclear cells (PBMCs) in horses experimentally infected with EHV-1. siRNA targeting two EHV-1 genes (glycoprotein B and the origin binding protein) was administered 12h before and 12h after intranasal infection with EHV-1. Control horses received siRNA targeting firefly luciferase. A significantly smaller proportion (0/10) of horses receiving siRNA targeting viral genes required euthanasia due to intractable neurologic disease as compared to horses in the control group (3/4; p=0.01). There was no significant difference in the presence of live virus or viral DNA in the nasal secretions or PBMCs between the two groups. Future studies are necessary to define the relative contributions of host and virus factors in the development of the neurological form of the infection and to determine an optimal dosing regimen for metaphylactic or therapeutic use of siRNA for treating EHV-1 infection.