NAVLE Respiratory

Equine Herpesvirus 1, 4, and 5 Study Guide

Equine herpesviruses (EHV) are among the most clinically significant viral pathogens affecting horses worldwide. The family includes nine identified herpesviruses, with EHV-1, EHV-4, and EHV-5 being the most important for NAVLE preparation.

Overview and Clinical Importance

Equine herpesviruses (EHV) are among the most clinically significant viral pathogens affecting horses worldwide. The family includes nine identified herpesviruses, with EHV-1, EHV-4, and EHV-5 being the most important for NAVLE preparation. These viruses are ubiquitous in horse populations, with estimates suggesting that 60-80% of horses harbor latent infections.

EHV-1 and EHV-4 are alphaherpesviruses that cause respiratory disease (rhinopneumonitis), while EHV-1 additionally causes abortion, neonatal foal death, and the devastating neurologic form known as equine herpesvirus myeloencephalopathy (EHM). EHV-5 is a gammaherpesvirus associated with equine multinodular pulmonary fibrosis (EMPF).

High-YieldEHV-1 is a USDA-APHIS designated emerging disease and is reportable in many states. When you see a horse with acute neurologic signs, fever, and recent transport or show history, EHV-1 myeloencephalopathy must be on your differential list.
Characteristic EHV-1 EHV-4 EHV-5
Subfamily Alphaherpesvirinae Alphaherpesvirinae Gammaherpesvirinae
Genus Varicellovirus Varicellovirus Percavirus
Genome dsDNA, 150 kbp dsDNA, 145 kbp dsDNA, 179 kbp
Latency Sites Trigeminal ganglia, lymphoid tissue, T lymphocytes Trigeminal ganglia, lymphoid tissue T and B lymphocytes

Viral Classification and Characteristics

Taxonomic Classification

EHV-1 Strain Variation: The D752/N752 Polymorphism

A critical concept for NAVLE is understanding the DNA polymerase (ORF30) single nucleotide polymorphism that distinguishes neuropathogenic from non-neuropathogenic strains. At amino acid position 752:

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