A disease of horses caused by a virus of the Orbivirus group. It affects all Equidae, but asses, mules, and zebra are more resistant than horses. The organism is transmitted by a mosquito and is highly infectious. It causes mainly respiratory signs, often with swelling of the head and neck. There is a high mortality rate, and the disease is notifiable in the UK. A vaccine is available which protects against some strains of the virus.
African horse sickness (AHS) is a highly infectious, and deadly disease. This disease can be caused by any of the nine serotypes of this virus. This disease is not directly contagious, but is known to be spread by insect vectors.
Epidemiology
This disease is known to be endemic in Sub Saharan Africa, and has spread to Morroco, the Middle East, India and Pakistan. Epidemiology is dependent on host-vector interaction where cyclic disease outbreaks coincide with high numbers of competent vectors.
Host
The common hosts of this disease are horses, mules, donkeys and zebra. However, elephants, camels and dogs (after eating infected horsemeat) can be infected as well, but often showing no signs of the disease.
Transmission
This disease is spread by insect vectors. However, this disease can also be transmitted by species of mosquitoes including Culex, Anopheles and Aedes, and species of ticks such as, Hyalomma and Rhipicephalus.
Clinical Signs
Horses are the most susceptible host with close to 100% mortality of those affected followed by mules (50%) and donkeys (10%). AHS manifests itself in four different forms: the Pulmonary form, the Cardiac form, Mild (Horse Sickness Fever) Form and Mixed form.
Pulmonary form
Preacute form of the disease characterised by high fever, depression and respiratory symptoms. This form of the disease has the highest mortality rate.
Cardiac form
Subacute form of the disease. The incubation period is longer than the Pulmonary form where signs of disease start at day 7-12 after infection.
Mild or Horse Sickness Fever form
Mild to subclinical disease is seen in zebras and African donkeys. Survival rate is 100%
Mixed form
Diagnosis at post-mortem exams.
Diagnosis
Persumptive diagnosis is made by characteristical clinical signs, post-mortem lesions and presence of competent vectors.
Treatment and Prevention
There is currently no treatment efficient enough to treat this disease.
Control of outbreak in an endemic region involves quarantine, vector control and vaccination. To prevent this disease the affected horses are usually slaughtered and the uninfected horses are vaccinated against the virus. This disease can also be prevented by destroying the insect vector habitats using insecticides.
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