Equid gammaherpesvirus 2 and equid gammaherpesvirus 5 infections

Equid gammaherpesvirus 2 and equid gammaherpesvirus 5 infections

Synonyms: Equid gammaherpesvirus infections, slowly cytopathic equid herpesvirus infections (formerly equid herpesvirus 2 and equid herpesvirus 5)

Previous authors: G P ALLEN AND M J MURRAY

Current authors:
M, CAROSSINO, DVM, PhD, Dipl. ACVM (Virology), Dipl. ACVP, Assistant Professor of Veterinary Pathology, Department of Pathobiological Sciences & Louisiana Animal Disease Diagnostic Laboratory (LADDL), School of Veterinary Medicine, Louisiana State University, Louisiana State University, United States
U B R BALASURIYA, BVSc, MS, PhD, FSLCVS, Director and Professor of Virology, Louisiana Animal Disease Diagnostic Laboratory (LADDL) & Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, River Road Room 1043, Baton Rouge, Louisiana, 70803, United States of America
M. E. BARRANDEGUY., DVM, PhD, Director, Research Institute, School of Veterinary Medicine, Universidad del Salvador, Buenos Aires, Argentina; Professor of Infectious Diseases, School of Veterinary Medicine, Universidad del Salvador, Buenos Aires, Argentina; Associate Principal Investigator, National Institute of Agricultural Technology (INTA), Buenos Aires, Argentina
Alan T. Loynachan, DVM, PhD, Dipl. ACVP, Professor of Veterinary Pathology, Veterinary Diagnostic Laboratory, Department of Veterinary Science, University of Kentucky, Lexington, KY 40511, United States of America


Equid gammaherpesviruses are a genetically heterogeneous viral subfamily characterized by a narrow host range, slow replication, lymphotropism, and widespread distribution in horse populations. Their interactions with their host are not fully elucidated and have been the subject of continued interest and research. Importantly, their widespread distribution and obscure pathogenicity has been a significant challenge in establishing an association with specific clinical and pathological conditions and in defining their significance from a diagnostic standpoint.

The prototype LK strain of equid gammaherpesvirus 2 (EHV-2), the first gammaherpesvirus to be recovered from the horse, was isolated in 1962 from the respiratory mucus of a foal with ‘catarrh and coughing’.80Since then, a great number of equid gammaherpesvirus isolates have been recovered from horses throughout the world.24, 27, 41, 48, 51, 56, 58, 90, 98, 101, 121 Twenty-five years elapsed before a subset of this large virus collection was recognized as sufficiently different to be classified as a second equid gammaherpesvirus type, equid gammaherpesvirus 5 (EHV-5).2, 20 To date, EHV-2 and EHV-5-associated infections are ubiquitous in horses around the globe. Characterized by extensive intratypic heterogeneity (both genetic and antigenic), a long replicative cycle, slow cell-to-cell viral infectivity, and low extracellular titres of infectious virus, the equid gammaherpesviruses comprise a complex and technically challenging group of herpesviruses for both equine virologists and practitioners.2, 3, 19, 21, 98

A large proportion of the world’s horse population carries gammaherpesviruses as a life-long latent infection of circulating B lymphocytes as well as a fluctuating, persistent and productive infection of epithelial cells of the nasopharynx, conjunctiva and cornea.16, 21, 32, 40, 56, 64, 65, 90, 91, 110, 112, 121 These viruses are intermittently shed from these mucosal surfaces of infected horses, and infected mares effectively transmit the infection to foals soon after birth, even in the presence of colostrum-derived antibodies.12, 19, 45, 48, 70, 108, 121 Although of low inherent pathogenicity, EHV-2 has been associated with several significant, clinically overt equine diseases, including syndromes involving the of upper and lower respiratory tracts of foals, keratoconjunctivitis, chronic follicular pharyngitis, and malaise and poor performance syndrome in young performing horses.6, 14, 25, 26, 29, 37, 45, 48, 51, 55, 74, 75, 91, 99, 100, 102, 106, 107 In the case of EHV-5, this equid gammaherpesvirus has been associated with a specific condition known as equine multinodular pulmonary fibrosis (EMPF).122, 124


Upon their original identification, EHV-2 and EHV-5 were recognized as ‘slowly cytopathic orphan herpesviruses’ of the domestic horse (Equus caballus)52, 72 and initially classified as equine cytomegalovirus-like betaherpesviruses within the subfamily Betaherpesvirinae.21, 41, 52, 94, 98, 115, 119 Equid gammaherpesvirus 2  and EHV-5 were indistinguishable from each other until the advent of restriction fragment length polymorphism analysis.104 Subsequent sequence analysis of their genomic DNA led to their reclassification within the subfamily Gammaherpesvirinae, genus Rhadinovirus.3, 104, 116 Since 2008, both EHV-2 and EHV-5 have been classified within the subfamily Gammaherpesvirinae, genus Percavirus31 (Figure 1) along with other gammaherpesviruses recognized in cats, ferrets, seals and bats. The two gammaherpesviruses have been historically distinguished by differences in electrophoretic mobilities, DNA restriction endonuclease cleavage patterns, titres of homologous versus heterologous antisera for neutralizing the two viruses, and Southern blotting. Currently, these techniques have been replaced by next generation sequencing of full-length genomes, which provides unparalleled...

To see the full item, register today:

Sign in to Anipedia

Forgot your username or password? Click here.

Not registered yet? Sign up now.

Start using Anipedia today, by creating your account.

Register now