EQUINE | CPD Article
Specific
• Presence of suitable vector and environmental
conditions to promote the vector.
• Contaminated veterinary equipment, infected
blood-containing products.
Pathophysiology
• Infection of endothelial cells of vascular system →
vasculitis → edema and hemorrhage.
Timecourse
• Variable depending upon clinical form but generally
5-14 days for the horse sickness fever; 3-5 days in
peracute (pulmonary) form; 5-7 days for mixed
form.
Epidemiology
• Virus is transmitted by night-flying biting insects,
especially Culicoides spp.
• There is evidence in enzootic areas of Africa of a
reservoir between seasonal attacks, probably in
zebras and donkeys.
• Incidence decreases to zero after cold weather in
temperate countries.
• Epidemics occur in cyclic intervals due to droughts
followed by heavy rains.
Diagnosis
Presenting problems
• Fever.
• Sudden death.
• Dyspnea.
• Peripheral edema.
• Respiratory distress.
• Sweating.
• Froth from nostrils.
• Paralysis of the esophagus.
• Pneumonia.
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Client history
• Horses in enzootic areas or in contact with horses
from these areas.
• Sudden death.
• Potential insect vectors.
• Epizootic outbreaks in Near East, Turkey, Iberian
peninsula.
Clinical signs
• Four forms of AHS are recognized, with the
pulmonary and mixed forms predominating in
susceptible populations. Zebras and donkeys rarely
develop serious clinical signs.
Acute/mixed form
• Combination of clinical signs of peracute
(pulmonary) and subacute (cardiac) forms.
• Rarely seen clinically but usually diagnosed at post-
mortem examination.
Horse Sickness fever form
• Mild signs.
• Partially immune horses or donkeys.
• Low grade fever (up to 39.5°C/103.1°F).
• Conjunctival congestion.
• Mild depression and inappetence.
• 5-8 days to recover (recovery common).
• Morning remissions and afternoon exacerbations
often seen.
Peracute/pulmonary form ('Dunkop')
• High fever (up to 41°C/105.8°F).
• Congested mucous membranes.
• Sudden onset severe respiratory distress.
• Dyspnea and tachypnea due to hydrothorax and
pulmonary edema - seen as extended head and
dilated nostrils.
• Spasmodic cough.
• Copious frothy nasal discharge (later).
• Rapid death 1-3 days; can be within hours of the
• Equine Health Update •