Page 643 - The Veterinary Care of the Horse

hyperplasia and ulceration of the pharynx.

• Equine herpesvirus-3 (EHV-3) causes venereal disease with lesions on the external
VetBooks.ir • genitalia.

Equine herpesvirus-4 (EHV-4) is also known as equine rhinopneumonitis virus. It

usually causes respiratory signs but occasionally results in abortion.
• Equine herpesvirus-5 (EHV-5) causes pneumonia and replacement of the lung tissue

with fibrous tissue.

EHV-1 and EHV-4 are the most common strains.

Clinical signs

Respiratory disease caused by EHV-1 and EHV-4 can affect any horse, but tends to occur in
groups of weaned foals and yearlings. The signs include:

• a raised temperature
• swollen glands under the mandible

• depression and lethargy

• loss of appetite

• watery nasal discharge which becomes purulent if secondary bacterial infection occurs

• coughing
• conjunctivitis.

Additional signs that can occur particularly with EHV-1 include the following.
• Equine infectious abortion, which can occur at any time between the 5th and 11th months

of gestation but most commonly occurs in late pregnancy and may be responsible for
single or multiple abortions; these often occur in the absence of any other clinical signs.

This can result in a so-called ‘abortion storm’ with several in-foal mares slipping or
losing their foals.

• The birth of weak, jaundiced foals that show respiratory distress and usually die within
three days.

• Swollen limbs.

• The paralytic form of equine herpesvirus presents as progressive incoordination and
weakness, sometimes leading to paralysis and a total inability to stand. These horses are

often unable to lift their tail or pass urine as a result of degenerative changes in the brain
and spinal cord caused by the virus. These signs often follow respiratory disease.