No protection seen on challenge with live virus after single intranasal immunization with heat inactivated virus in murine model of EHV-1 infection

Abstract

Equine herpes virus (EHV-1) causes respiratory disease, abortion, neonatal death, paresis, retinopathy, and latent infection and is wide-spread among equine worldwide. Horses show transient immunity after natural or experimental EHV-1 infection and immune responses to EHV-1 begin to decline after a few months after infection. As a result, recovered horses are prone to subsequent EHV-1 infection. Due to transient immune responses, effective and lasting vaccination remains a challenge. As this virus is widespread among equine, development of effective vaccine is a challenge. We used a murine model to study the efficacy of heat inactivated virus in terms of protection in a challenge study. After 34 days following intranasal inoculation with heat inactivated virus, mice were challenged with live virus along with previously placebo control group. Clinical signs, virus titres, and viraemia were studied in both groups. We noticed that mice on challenge showed more clinical signs at peak of infection but no significant difference in virus titres and infectious centre assay was noted. The results of this study suggest that heat inactivated virus does not provide any protection to challenge dose but in fact these group looked clinically worse. These results are discussed along with the possible mechanism involved in more clinical signs seen on challenge after single dose of intranasal immunization by heat inactivate virus in current communication.