What are African Horse Sickness?
The disease can occur in cardiac or respiratory forms, with respiratory symptoms including dyspnea, coughing, and frothy fluid coming from the mouth and nostrils. Recovery from this form of the disease is rare. In the cardiac form of AHSV, swelling of the facial tissue, eyelids, neck and chest may be seen.
The mortality rate of this disease may vary depending on the form taken, however horses who are showing symptoms suggestive of this disease should be seen by a veterinarian and quarantined from other animals.
African horse sickness virus (AHSV) is a viral disease transmitted by the biting midge. This disease is endemic to sub-Saharan Africa, however outbreaks have been seen in Egypt, the Middle East and Southern Arabia. During one outbreak the disease extended to Pakistan and India, and was estimated to kill at least 300,000 horses. The virus thrives during hot, humid weather and cold weather will often cause epidemics to end.
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Symptoms of African Horse Sickness in Horses
- Standing with forelegs splayed
- Neck extension
- Fully dilated nostrils
- Nasal discharge
- Severe depression
African horse sickness can take four different forms:
This form usually presents with an acute, high grade fever leading to severe respiratory distress.
Subacute Edematous (cardiac)
This form usually presents with a fever which subsides after a week, leading to swelling around the eyes. This swelling may then spread to the face, tongue, throat, top of the legs and chest. Unfortunately, this form of the illness is often fatal.
This form often has subclinical cardiac signs which are then followed by the sudden onset of severe respiratory distress.
Horses suffering from this form usually present with fever that worsens in the evenings, other symptoms may include mild anorexia and facial swelling. The prognosis for full recovery is good in this form.
Causes of African Horse Sickness in Horses
AHS mainly affects equids – horses, mules, donkeys and zebras, but is also seen in dogs. This illness is caused by the animal becoming infected with the virus African Horse Sickness, a member of the genus Orbivirus from the family Reoviridae.
African horse sickness is transmitted by insects known as midges. It is thought that mosquitoes, biting flies, the camel tick, and dog tick may also transmit the disease.
Although horses are only symptomatic from 4-8 days the virus can live in the blood for as long as 21 days. It is not known how long horses are infectious following infection, however this is not spread through contact between horses. Dogs, as well as horses, can be infected by this virus, usually following the consumption of contaminated horse meats.
Diagnosis of African Horse Sickness in Horses
Your veterinarian will first observe your horse from a distance to check for abnormalities that may not be visible while restrained. He will note your horse’s respiratory rate and effort. If your horse is suffering from dyspnea, your veterinarian will closely watch the character of this. Your veterinarian will then examine all the major organs and auscultate the lungs, heart and digestive system. Your horse’s temperature will be taken, if your horse is suffering from AHSV a fever will be expected.
If your veterinarian suspects AHSV there are virological methods that can be used to test for the virus. A blood test may be taken that when tested may show AHSV antigens present in the blood. Other testing that may be performed is serology which may show antibodies from 8-14 days following infection.
Treatment of African Horse Sickness in Horses
Unfortunately, there is no cure for African horse sickness, however supportive care may be offered. For example, medications and therapy to alleviate colic may be offered. Fever will be addressed with medication to reduce it, and if there is a need for oxygen supplementation, this will be provided.
Recovery of African Horse Sickness in Horses
The prognosis for a horse infected by AHSV differs depending on numerous factors including underlying conditions, the form the disease takes, and immunity through previous infection or vaccination. If the horse has been infected with the fever form prognosis is good, however, recovery following pulmonary or cardiac infection is rarer.
In animals that recover, a good immunity is often developed, meaning chances of reinfection are lesser. There is a live attenuated vaccine available to horses living in endemic areas, although cases have still been seen in horses who have received the vaccination.
To reduce the chance of transmission it is recommended that in areas where the virus is endemic horses are kept in insect-proof stables, particularly from dusk to dawn as this is when the insects that can cause transmission are most active.
To further manage the spread and introduction of AHS there are strict quarantine regulations for horses entering non-endemic countries such as the U.S. This includes a 60 day quarantine period and blood testing.