AETIOLOGY
Classification
of the causative agent African horse sickness (AHS) is caused by a
virus of the family Reoviridae of the genus Orbivirus.
EPIDEMIOLOGY
Infectious
disease is transmitted by Culicoides spp. that occurs
regularly in most countries of subSaharan Africa
At
least two field vectors are involved: Culicoides imicola and C.
bolitinos
The
disease has both a seasonal (late summer/autumn) and an epizootic
cyclical incidence, with disease associated with drought followed by
heavy rain
Usual
hosts are equids: horses, mules, donkeys and zebra
Reservoir
host are believed to be zebras
Clinical
diagnosis
There
are four principal manifestations of disease
In
the majority of cases, the subclinical cardiac form is suddenly
followed by marked dyspnoea
Fever
(40–40.5°C/104°F–105°F)
Mild
form; general malaise for 1–2 days
Subacute
or cardiac form
Fever
(39–41°C/102–106°F)
Swelling
of the supraorbital fossa, eyelids, facial tissues, neck, thorax,
brisket and shoulders
Mortality
usually 50% or higher; death usually within 1 week Acute respiratory
or
pulmonary
form
Fever
(40–41°C/104–106°F)
Dyspnoea,
spasmodic coughing, dilated nostrils with frothy fluid oozing out
Redness
of conjunctivae
Mixed
form (cardiac and pulmonary)
Occurs
frequently
Pulmonary
signs of a mild nature that do not progress, oedematous swellings and
effusions
Mortality:
about 70–80% or greater Lesions
Respiratory
form: interlobular oedema of the lungs o hydropericardium,
pleural effusion oedema of thoracic lymph nodes petechial
haemorrhages in pericardium mucosa and serosa of small and large
intestines may exhibit hyperaemia and petechial haemorrhages
Cardiac
form: o subcutaneous and intramuscular gelatinous oedema epicardial
and endocardial ecchymoses; myocarditis o hemorrhagic gastritis
PREVENTION
AND CONTROL
- No efficient treatment available Sanitary prophylaxis Free areas, regions and countries Identify the virus and serotype
- Establish strict quarantine zone and movement controls
- Consider euthanasia of infected and exposed equids
- Stable all equids in insect-proof housing, at a minimum from dusk to dawn when Culicoides are most active
- Establish vector control measures: destroy Culicoides breeding areas; use insect repellents, insecticides, and/or larvicides
- Monitor for fever at least twice daily: place pyrexic equids in insect-free stables or euthanize
- Consider vaccination o identify vaccinated animals o available vaccines are attenuated produce viraemia, and may theoretically reassort with the outbreak virus may be teratogenic Affected areas, regions and countries
- Annual vaccination
- Vector control
References
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