African horse sickness

A viral disease affecting horses and other equids

African horse sickness (AHS) is a highly infectious and often fatal disease that affects horses, mules, and donkeys. It is caused by the African horse sickness virus (AHSV), which is an arbovirus of the genus Orbivirus within the family Reoviridae. The disease is endemic to sub-Saharan Africa but can spread to other regions through infected Culicoides midges, which are the primary vectors.

Virology

The African horse sickness virus is a double-stranded RNA virus with a segmented genome. There are nine known serotypes of AHSV, each capable of causing disease. The virus primarily targets the endothelial cells of blood vessels, leading to increased vascular permeability and subsequent clinical signs.

Transmission

AHS is primarily transmitted by Culicoides midges, which are small biting insects. The virus can also be spread through direct contact with infected animals or through contaminated equipment. The disease is not contagious between horses without the presence of the vector.

Clinical signs

The clinical presentation of African horse sickness can vary depending on the form of the disease. There are four main forms:

• Pulmonary form: Characterized by severe respiratory distress, coughing, and frothy nasal discharge. This form is often fatal within a few days.
• Cardiac form: Marked by swelling of the head and neck, fever, and colic. Death can occur within a week.
• Mixed form: A combination of both pulmonary and cardiac symptoms.
• Horse sickness fever: A milder form seen in partially immune animals, with fever and mild clinical signs.

Diagnosis

Diagnosis of AHS is based on clinical signs, serology, and polymerase chain reaction (PCR) testing to detect viral RNA. Virus isolation can also be performed in specialized laboratories.

Prevention and control

Preventive measures include vaccination, vector control, and movement restrictions. Vaccination is the most effective method of control, with live attenuated vaccines available for use in endemic areas. Controlling the midge population through insecticides and environmental management can also help reduce transmission.

Epidemiology

AHS is endemic in sub-Saharan Africa but has the potential to spread to other regions through infected vectors. Outbreaks have occurred in North Africa, the Middle East, and Europe, often associated with the movement of infected animals or vectors.

Impact

African horse sickness has a significant impact on the equine industry, causing high mortality rates and economic losses. The disease can also affect wildlife, with zebras acting as a reservoir host.

Related pages

• Equine infectious diseases
• Orbivirus
• Culicoides
• Reoviridae

Gallery

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  Structure of the African horse sickness virus
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  Clinical signs of African horse sickness
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  Transmission cycle of African horse sickness