Inside South Africa’s ongoing battle against a disease that every horse owner knows by name.
By Charlene Carroll
The sun dips behind the veld, the air thick with the hum of insects, and somewhere in the stable yard a horse stamps uneasily at the persistent buzz of midges. To most, they’re just an evening nuisance. To South African horse owners, they represent something far more sinister, the invisible carriers of a disease that has shaped equestrian life for over two centuries.
African Horse Sickness, or AHS, is not just another equine illness; it’s a part of our national equine history, a threat that lingers in every flick of a tail and every watchful night in summer. And no matter how much we think we know about this disease, there is always more to know!
Understanding the disease
AHS is a viral disease transmitted primarily by the Culicoides midge, a tiny biting insect that thrives in warm, humid conditions. The virus attacks the circulatory and respiratory systems of horses, causing fever, swelling, and, in its most acute form, respiratory failure. The mortality rate can be devastating, amounting to up to 90% in unvaccinated horses.
While donkeys and zebras often carry the virus with little to no symptoms, horses are tragically the most susceptible. It’s a cruel irony that South Africa’s strong equestrian culture coexists with one of the world’s most lethal horse diseases. And it’s one we’ve come to know intimately, because we’ve had no choice.
A long history of heartbreak
Records of AHS stretch back to the late 18th century, when outbreaks wiped out cavalry horses and transport animals across parts of the Cape region. It reshaped the development of horse breeds and riding culture in the region, forcing settlers and farmers to adapt their management practices for survival.
Since then, AHS has been a recurring spectre, reappearing in waves whenever conditions are right. The disease has influenced everything from horse export regulations to stable design. The establishment of controlled zones, with the AHS-free area in the Western Cape serving as the country’s lifeline for international trade, is just one of the many ways South Africa has learned to live with the risk.
For those who breed, train, or compete at the highest levels, understanding AHS is as fundamental as knowing how to saddle a horse.
The science and struggle of vaccination
Vaccination is our best defence, but it’s far from simple. South Africa uses a live attenuated vaccine, developed decades ago, that provides protection against multiple AHS virus strains. Because it’s a live vaccine, it must be administered during designated windows to avoid interference with natural transmission cycles and to allow authorities to track potential reactions.
For many owners, that means timing is everything. Miss the window and your horse remains unprotected through the risky summer months. Vaccinate too soon or too late, and you could find yourself on the wrong side of regulatory restrictions or biosecurity rules. It’s a balancing act that requires precision and, sometimes, a little luck.
Availability has also been an issue in recent years. Production challenges have caused delays, leaving owners frustrated and anxious as midge season looms. The South African equine community has become adept at sharing information, supporting one another through shortages, and lobbying for consistency, all while never losing sight of why vaccination matters. As one Pretoria-based vet put it, “We may grumble about the timing and the red tape, but every jab we give is a life we might save.”
Living with vigilance
For those outside South Africa, AHS might seem like a distant threat. For those who live with horses here, it’s an annual reminder of both nature’s power and our responsibility as caretakers. The disease has shaped who we are as a community, resilient, disciplined, and united in purpose.
There’s optimism, too. Ongoing research into new-generation vaccines promises greater safety and easier administration. Climate modelling is improving our ability to predict outbreaks, giving owners time to prepare. And, year after year, the equestrian world in South Africa continues to grow, proof that passion outweighs fear.
At the end of the day, when the last stable light is switched off and the horses settle for the night, every owner knows the truth: AHS demands respect, not panic. Vigilance, not complacency. And above all, care.
AHS Prevention: Quick-Checklist for Horse Owners
Vaccinate each year: In certain zones, annual vaccination with a registered vaccine is a legal requirement.
Stable horses between dusk & dawn: The biting midges are most active at dawn and dusk, keep horses indoors during those hours.
Ensure stable is midge-proof: Install fine-mesh screens on windows/doors, use fans for airflow.
Remove/avoid standing water: These are breeding grounds for midges, ensure good drainage, clean up puddles, avoid turnout near wetlands.
Use insect repellent & protective gear: Apply approved repellents on horses; use fly-sheets, masks, or ear covers.
Manage stable yard hygiene: Remove manure regularly, keep bedding clean and dry, and manage feed/water troughs.
Monitor paddocks: Inspect paddocks and the yard for wet spots and excess vegetation that may harbour midges.
Avoid moving horses: Check vaccination status prior to movement, as movement can introduce risk.
Stay alert for early signs: Check horses’ temperatures and observe for anything unusual (fever, swelling around eyes/face, coughing).
Early symptoms of AHS
Fever: a sudden rise in temperature (often around 39–41 °C).
Lethargy or depression: the horse appears dull, less responsive, wary or “off” its normal self.
Loss of appetite: the horse may refuse food or not eat as well.
Difficulty breathing: early signs include faster breathing, coughing or laboured respiration.
Profuse sweating: especially with the pulmonary form — the horse may sweat more than usual without strenuous exercise.
Nasal discharge (frothy or foamy): in some cases, early discharge may appear before more dramatic signs.
Swelling/oedema: particularly around the head, neck, eyelids, supra-orbital fossae (above the eyes) in the cardiac form.
Gum or eye membrane changes: reddening of mucous membranes or small haemorrhages may occur.
Signs of colic or discomfort: in cardiac/subacute forms, there may be abdominal pain, pawing or rolling.
Onset: symptoms typically appear about 5-7 days post-infection in many cases (though incubation may vary).
Dunkop (pulmonary form)
This is the most rapid and severe manifestation. Affected horses show sudden high fever, severe respiratory distress (coughing, frothy nasal discharge, laboured breathing), and often die within hours to a few days.
Dikkop (cardiac or oedematous form)
This form develops slightly more slowly. After a febrile period, horses show marked swelling of the head/neck/eyelids (oedema), and signs consistent with circulatory failure. Mortality is lower than the pulmonary form but still high.
Mixed (acute) form
A combination of both pulmonary and cardiac signs, respiratory distress, plus oedema. This is often the most common form seen in outbreaks and carries a very high fatality rate.
Horse sickness-fever (mild/subclinical) form
The mildest form. Horses with partial immunity may show only fever, depression or mild swelling and generally recover.
