African horse sickness (AHS) is a deadly viral disease that primarily affects horses, but it can also infect mules, donkeys, and zebras. Caused by the African horse sickness virus (AHSV), it’s spread through biting midges—tiny flying insects most active at dawn and dusk. AHS is most prevalent in sub-Saharan Africa but has caused serious outbreaks in North Africa, the Middle East, and parts of Europe. Because of its high mortality rate and ability to spread rapidly, it’s classified as a notifiable disease by the World Organisation for Animal Health (WOAH).
There are nine known strains (serotypes) of AHSV, and infection with one doesn’t necessarily protect against the others. This makes management and prevention a complex challenge for vets and horse owners in regions where the disease is endemic.
Symptoms of African Horse Sickness
The symptoms of AHS vary depending on the form of the disease, of which there are four: pulmonary (lung), cardiac (heart), mixed, and mild or horse sickness fever.
- The pulmonary form is the most severe, often leading to death within 48 hours. It begins with fever, difficulty breathing, coughing, and frothy discharge from the nostrils.
- The cardiac form progresses more slowly, over 4–8 days, with swelling (edema) of the head, neck, and eyelids, fever, and depression.
- The mixed form combines features of both cardiac and pulmonary, leading to rapid deterioration and a high death rate.
- The mild form, more commonly seen in zebras and donkeys, usually presents as a low-grade fever and slight discomfort but rarely results in death.
If your horse suddenly develops fever, labored breathing, or swelling in the face, immediate veterinary attention is crucial.
How is AHS Transmitted?
AHS is transmitted almost exclusively by biting midges of the Culicoides genus, particularly Culicoides imicola. These insects breed in warm, moist environments and are most active at dawn and dusk. Horses become infected when bitten by a midge carrying the virus, which they may have picked up from an infected animal.
Unlike some other infectious diseases, AHS is not spread through direct contact between animals. That means horses can’t pass it to each other by sharing food, water, or space. However, the virus can spread quickly through a herd if infected midges are present, especially in warmer climates.
Zebras, while usually resistant to symptoms, are considered natural reservoirs for the virus. They can harbor the disease without showing signs, allowing midges to pick up and spread the virus unknowingly.
Can AHS Affect Humans?
No, African horse sickness does not affect humans. It is a disease strictly limited to equines and is not considered a zoonotic threat. Humans cannot catch AHS from horses, midges, or by handling infected animals.
That said, outbreaks can have significant economic and emotional impacts on communities that rely on horses for transport, labor, or sport, especially in rural and developing areas.
How Is AHS Treated and Prevented?
There is currently no cure for African horse sickness once a horse is infected. Treatment is mostly supportive and may include anti-inflammatory medications, fluids, and rest. Unfortunately, due to the high mortality rate, especially in the pulmonary and mixed forms, prevention is far more effective than trying to treat the disease.
Prevention strategies include:
- Vaccination: In endemic areas, vaccines—both live attenuated and inactivated—are used to protect horses. These are typically administered annually or seasonally depending on the local climate and midge activity.
- Vector control: Managing the midge population is critical. This can involve stable screens, insect repellents, and avoiding turnout at dawn and dusk when midges are most active.
- Movement restrictions: In the event of an outbreak, restricting the movement of horses helps prevent the disease from spreading to new areas.
- Monitoring and reporting: Prompt reporting to authorities ensures swift action can be taken to contain and manage outbreaks.
If you live in or travel to an area where AHS is present, consult with your vet about vaccination schedules and practical prevention measures.
Protecting Equine Health from African Horse Sickness
African horse sickness is a serious and often fatal disease that requires awareness, prevention, and fast action. Though it does not affect humans, it has a devastating impact on equine populations, particularly in countries where vector control is difficult. Through a combination of vaccination, insect control, and responsible reporting, the spread of AHS can be managed—and lives can be saved. If you’re a horse owner in an affected area or plan to travel with horses, always prioritize education and prevention.
