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Equine herpesvirus, aka Rhinopneumonitis (Rhino), is a common DNA virus that occurs in horse populations worldwide. The two most common strains are EHV-1, which causes abortion, respiratory disease and neurologic disease; and EHV-4, which usually causes respiratory disease only but can occasionally cause abortion. Respiratory disease caused by EHV is most common in weaned foals and yearlings, often in autumn and winter. Older horses are more likely than younger ones to transmit the virus without showing signs of infection. Herpesvirus myeloencephalitis cases occur singly or as outbreaks affecting 20-50% of the population.Quick resources for Horse owners: Frequently asked questions about EHV/EHM and EHV/EHM brochure for the horse owner
Clinical Signs
Respiratory disease
- Fever—commonly precedes other clinical signs, but may be the only clinical sign
- Coughing / Respiratory distress
- Nasal discharge
- Weakness
- Jaundice (yellow color to gums and whites of eyes
Abortion – Occurs with no warning during late pregnancy (8+ months); occasionally as early as 4 months.
Neurologic disease:
- Incoordination of the hind (and occasionally fore) limbs, dog sitting posture
- Urine retention/dribbling
- Recumbency – down unable to stand
- Neurologic signs may be preceded by fever and respiratory signs.
Transmission
- Aerosol transmission (most common route) -Inhalation of droplets from coughing and snorting.
- Indirect transmission through fomites – buckets, boots, clothing, etc.
- Aborted fetuses, fetal membranes and/or fluids are significant sources of infection.
Incubation
- The incubation period for the disease (time between exposure and clinically apparent illness) is one to 14 days.
- Infected horses usually will shed virus into the environment for seven days or less, but in some cases they can shed for two weeks or longer.
- Horses can be infected with EHV-1 without showing signs of disease, but they can still shed the virus and infect other horses (as asymptomatic carriers).
- It is recommended that any horse that is potentially exposed to equine herpesvirus be quarantined for a minimum of 3 weeks.
Environmental contamination/disinfection
The virus lives probably less than 7 days in most environments, but can survive for up to 35 days. Routine disinfectants such as a 10% bleach solution are effective for disinfecting the environment. Remember to clean buckets, stalls, and shovels/pitchforks.