Research Accomplishment Reports 2007

 

Reactivation and Transmission of Latent Equine Herpesvirus-1 in Pregnant Mares: Role as Risk Factors for Equine Herpesvirus Abortion

G.P. Allen
Department of Veterinary Sciences

 

Project Description

Abortion in pregnant mares resulting from infection of the fetus with equine herpesvirus-1 (EHV-1) represents a common and agriculturally important disease entity with the potential for causing severe economic losses to the equine breeding industry.  A central event in the etiology of EHV-1 related abortion is reactivation of the herpesvirus from its inactive, latent state within tissues of the carrier broodmare. 

The primary objective of this project was to better understand the frequency, scope of viral transmission, and risk factors associated with reactivation of EHV-1 from latency.  This objective was achieved by a multi-year serological and virological monitoring for the reactivation and spread of latent EHV-1 in an experimental group of 30 pregnant broodmares in which EHV-1 latency had been experimentally established.  The overall profile of reactivation of EHV-1 in minimally managed, non-pregnant mares was characterized by a low reactivation frequency with minimal shedding and transmission of the reactivated virus (silent reactivation events). By contrast, mares exposed to stress-inducing management practices (e.g., pasture breeding, pregnancy, foaling, nursing, mixing of mare groups) or stress-inducing environmental events (e.g., respiratory disease caused by equine influenza virus or EHV-4) exhibited more frequent reactivation events some of which resulted in subsequent transmission of virus infection to seronegative sentinel herdmates or in clinical neurological disease. 

The results emphasize the importance of stress reduction in broodmare management practices and provide a scientific foundation for recommending herd health intervention strategies for reducing the risk for mare abortions caused by EHV-1.

Impact

his research project has experimentally demonstrated the establishment of equine herpesvirus-1 latency in pregnant broodmares, monitored the reactivation and subsequent transmission of the latent herpesvirus to herdmates, and identified farm management associated risk factors for viral reactivation. It is anticipated that such information obtained from this project will be practicably applicable to efforts aimed at optimal maintenance of the health, reproductive success, and economic profitability of the equine breeding segment of the nation's agriculture. We also expect that knowledge drawn from these experiments will illuminate some general aspects of the complex biology of the equine herpesvirus-1 pathogen, particularly in the areas of the establishment and reactivation of herpesvirus latency and of transmission patterns of the reactivated viral pathogen.

Publications

Allen, G.P., and Breathnach, C.C. (2006). Quantification by Real-Time PCR of the Magnitude and Duration of Leukocyte-Associated Viraemia in Horses Infected with Neuropathogenic Versus Non-Neuropathogenic Strains of Equid Herpesvirus-1, Equine Veterinary Journal, 38: 252-257.

Allen, G.P. (2006). Antemortem Detection of Horses Latently Infected with Neuropathogenic Strains of Equine Herpesvirus-1, American Journal of Veterinary Research, 67: 1401-1405.

Allen, G.P. (2007). Development of a Real-Time Polymerase Chain Reaction Assay for Rapid Diagnosis of Neuropathogenic Strains of Equine Herpesvirus-1, Journal of Veterinary Diagnostic Investigation, 19: 69-72.

Allen, G.P. (2008) Risk Factors for Post-Exposure Development of Equine Herpesvirus-1 Neurological Disease. American Journal of Veterinary Research (in press).

Allen, G.P., Bolin, D.C., Bryant, U., Carter, C.N., Giles, R.C., Harrison, L.R., Hong, C.B., Jackson, C.B., Poonacha, K., Wharton, R., and Williams, N.M. (2008). Prevalence of Latent, Neuropathogenic Equine Herpesvirus-1 in the Thoroughbred Broodmare Population of Central Kentucky, Equine Veterinary Journal (in press).