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Pathogen Page

Equid herpesvirus

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Equine Rhinopneumonitis

3. Introduction

In equids eight herpesviruses have been identified: five belong to the subfamily alpha herpesvirinae and three to the gamma herpesvirinae. The horse is the natural host to alphaherpesvirus types 1 (EHV-1), 3 (EHV-3 coital exanthemavirus), 4 (EHV-4) and gammaherpesvirus types 2 (EHV-2) and 5 (EHV-5). Until 1981, EHV-1 and EHV-4 were considered as two subtypes of the same virus, namely EHV-1. Both EHV-1 and EHV-4 are endemic in horse populations worldwide. Prior to 1981, a single virus ‘EHV-1’ was known as the cause of febrile rhinopneumonitis, ataxia, abortions and neonatal foal disease in horses (Allen and Bryans, 1986). However, it should be stated that as early as 1972 most ‘EHV-1’ strains were distinguishable as respiratory (subtype 2) and abortigenic (subtype 1) viruses. Acute, naturally occurring respiratory diseases due to EHV-1 and EHV-4 are characterised by fever, anorexia, nasal discharge of varying severity and ocular discharge. Bacterial proliferation in nasal passages may be a contributory factor in the development of rhinopneumonitis. Experimentally, however, EHV-1 causes a much more severe disease than that induced by EHV-4 (Patel and Heldens, 2005).

4. Microbial Pathogenesis

Primary EHV-1 replication occurs in the upper respiratory tract epithelial cells and local lymph nodes resulting in leukocyte-associated viremia. Leukocyte associated viremia in acute infection has been shown as a prerequisite for abortion and paresis by initiating replication of EHV-1 in the endothelial lining of blood vessels in the central nervous system (CNS) and pregnant uterus. A widespread infection of endometrial blood vessels results in severe vasculitis and multifocal thrombosis, which could result in an abortion of a virus negative fetus. Latency has been demonstrated in lymphoid and neural tissues for both EHV-1 and EHV-4 (Patel and Heldens, 2005).

5. Host Ranges and Animal Models

Equids

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