FieldDxEquine herpesvirus-1 and equine herpesvirus-4 infectionsClinical signs, differential diagnosis, treatment and prevention in horses.
Overview
Common viral infections of horses ranging from mild respiratory disease to abortion or neurologic disease. Equine herpesvirus-1 (also causing abortion and neurologic disease) or equine herpesvirus-4 (mainly respiratory).
Clinical signs
- Neurologic disease (equine herpesvirus myeloencephalopathy) and/or abortion.
Predisposing factors
- Spread by nasal secretions (direct contact, fomites or aerosol) and by aborted fetuses, placentas and placental fluids.
- Stress triggers viral reactivation, shedding and new infections.
- Respiratory outbreaks occur yearly in foals and younger performance horses in concentrated horse populations.
- Outcome depends on viral strain, immune status, pregnancy status and possibly age; the virus can stay viable on common surfaces for about 48 hours.
Look-alikes to rule out
Treatment
Treatment is largely supportive (NSAIDs, rest, nursing care); antiviral drugs have been used specifically for the neurologic form (equine herpesvirus myeloencephalopathy, EHM).
Prevention
1. Three-tiered approach to managing an outbreak of equine herpesvirus myeloencephalopathy:1. 2. Segregation: Segregate the population into small discrete groups that can be managed discretely to avoid infection transferring between them 2.2. 3. Testing: Test a partial set from all animals with nasopharyngeal (NP) swab by qPCR and serum by complement fixation test (CFT) 1.3.
Source
MSD Veterinary Manual — Equine Herpesvirus Myeloencephalopathy (accessed 2026-08-11)
MSD Veterinary Manual — Equine Herpesvirus Infection (accessed 2026-10-29)
A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER (Passage 71); (Passages 154, 155 / Index).
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