Signs and symptoms
With a respiratory infection there is often serous discharge from the nose and eyes, but not a lot of coughing. Additionally, lymph nodes under the jaw may be constantly enlarged. Generally, respiratory signs are minimal when it comes to the neurological form, but the horse will have a fever of
38.5°C or more.
Neurological disease appears suddenly and usually progresses rapidly, reaching its peak within 24-48 hours from the onset of the initial neurological signs. Horses infected with EHV-1 strains often develop a fever, with a second temperature peak on the sixth and seventh days.
Secondary bacterial infections are common and are accompanied by nasal discharge and pulmonary disease. Other signs include:
A lack of coordination
Hindlimb weakness
Loss of tail tone
Lethargy
Urine dribbling
Head tilt
Leaning against a fence or wall to maintain balance
Inability to get up
Pregnant mares who abort after EHV-1 infection rarely display signs other than the abortion at the time. Abortions occur between two and 12 weeks after infection — usually in the last trimester, between the seventh and 11th month of gestation. Sometimes, but not always, abortion storms occur a few weeks after an outbreak of respiratory disease. Mares exposed late in gestation may not abort, but give birth to live foals with pneumonia. These foals are susceptible to secondary bacterial infections and usually die within hours.