Since the summer of 2025, one name has kept coming up in every yard in the south of France: the West Nile virus. In 2026, West Nile fever has become the most active vector-borne disease in horses across the country, with a circulation that spreads well beyond its historic home in the Camargue. Here we offer a full, non-alarmist overview: where this disease comes from, how to recognise it, and above all how to protect your horse before the mosquitoes return.
A disease born far from our yards
The virus owes its name to pure geographical chance. It was first isolated in 1937 in the West Nile district of Uganda, in a woman suffering from fever. For decades, it remained an African curiosity, responsible for small outbreaks of fever in Africa and the Near East. It then travelled, carried by migratory birds, until it caused notable epidemics around the Mediterranean, and then in the United States in the late 1990s.
In France, it is nothing new: the Camargue has known it since the 1960s, and equine outbreaks have reappeared regularly in the south since the early 2000s. What changes in 2026 is the intensity and extent of its circulation.
Where do we stand in 2026?
The figures speak for themselves. As of 21 August 2026, the French equine disease surveillance network (RESPE) counted 93 confirmed equine cases in France, including 53 in Occitanie and 33 in Provence-Alpes-Côte d'Azur. This total alone already exceeds the number of cases from the two previous years combined, even though the peak of the epidemic did not yet appear to have been reached.
The season's first cases had been detected in early August in the Pyrénées-Orientales, before the virus spread towards the Gard, the Hérault and the whole Mediterranean rim. On the human side, a handful of locally acquired cases were reported, which explains the heightened vigilance of the health authorities. But beware of one stubborn misconception: your horse cannot infect you.
How the virus circulates (and why the horse does not transmit it)
The West Nile virus cycle relies on two main players: wild birds, which are the natural reservoir of the virus, and mosquitoes, mainly of the Culex genus, which make the link. A mosquito bites an infected bird, picks up the virus, then transmits it by biting another host.
The horse, like the human being, is an accidental host, or "epidemiological dead end". This means it can fall ill, sometimes seriously, but does not develop enough virus in its blood to re-infect a mosquito. There is therefore no transmission from horse to human, nor from one horse to another, nor from human to human. The only route of infection is the mosquito bite. This is good news: it means all prevention can focus on a single enemy, the mosquito.
A field anecdote: birds act as silent "sentinels". Unusual mortality among corvids (crows, magpies) in a region can precede the first equine cases. It is one of the signals epidemiologists watch for.
Recognising the symptoms
The vast majority of infected horses, around 80%, show no sign at all. Among those that do develop the disease, most present mainly with fever and passing dullness. Only a minority, estimated at between 1 and 10% of cases, develops the neurological form, the most feared.
After an incubation phase of a few days, the signs to watch for are:
- a fever and a decline in general condition, a loss of appetite;
- behavioural disturbances: marked dullness or, on the contrary, hyperexcitability;
- muscle tremors, particularly in the head and neck;
- a loss of motor coordination (ataxia): the horse staggers, stumbles, seems "drunk";
- in severe forms: difficulty getting up, paralysis, up to coma.
The neurological form can be fatal or leave lasting effects, even after recovery. Conversely, many affected horses recover within three to four weeks with suitable care. The watchword: at the slightest neurological sign, call the vet without delay. Keeping a daily record of your horse's vital signs helps spot a fever or unusual behaviour very early.
A notifiable disease
West Nile fever is classified as a category 1 health hazard in France. In concrete terms, any suspected case must be reported to the authorities: your vet triggers the analyses with the reference laboratory and informs the state services. This notification is not a penalty for you, it is what allows the circulation of the virus to be mapped and the whole industry to be protected. So do not see it as a constraint, but as a useful act for the entire equestrian community.
What treatment in the event of infection?
There is no specific treatment against the West Nile virus, in horses or in humans. Care is purely symptomatic and aims to support the animal while its body fights the infection. The vet may:
- settle the horse in a quiet box, with dimmed light and protected from insects;
- set up rehydration (fluid therapy);
- administer anti-inflammatories to limit the nerve inflammation;
- provide vitamin support (vitamins C and B1) and, if needed, tranquillisers to ease the symptoms.
Good nursing, close monitoring, help getting up, maintaining hydration and feeding, often makes the difference in severe forms. Hence the value of a well-coordinated team around the horse.
Prevention: vaccination first and foremost
Since there is no treatment, prevention is your best weapon, and vaccination remains the most effective means. Vaccines exist and are marketed in France for horses. The standard protocol relies on a primary vaccination in two injections a few weeks apart (generally four to six), possible from five to six months of age, followed by an annual booster.
The crucial point is the timing. Immunity takes several weeks to build up after the second injection, and it lasts about a year. As the mosquito season runs from May to November, the ideal is to vaccinate in spring, so that protection is complete before the vectors arrive. If you go about it when the first cases are announced, it is already a little late. Talk it over with your vet as early as winter, especially if you live in or travel to a high-risk area in the south of France. So you forget nothing, our vaccination and worming calendar gives you clear pointers, and you can combine it with the calendar of the other essential horse vaccines.
Prevention: fighting mosquitoes
Vaccination does not remove the need to reduce exposure to bites. Culex mosquitoes are most active at dusk, at night and at dawn. A few simple actions lower the pressure:
- Adjust turnout times: bring the horses in or limit field time during the hours of high mosquito activity, at the start and end of the day.
- Eliminate standing water: water troughs renewed regularly, buckets emptied, gutters and tarpaulins cleared of still water, that is where mosquitoes lay their eggs.
- Protect physically: repellents suited to horses, fly sheets and fly masks, mosquito netting over the box openings.
- Ventilate: a fan in the stable hampers the mosquitoes' flight.
These measures also protect against many other summer nuisances. Above all they require consistency, which is easier when the whole team around the horse plays its part.
Staying calm thanks to organisation
Faced with a closely monitored disease, the best attitude is not worry but method: a horse vaccinated in time, an environment unfavourable to mosquitoes, and careful daily observation. When several people look after the same horse, owner, sharer, club riders, it is coordination that creates safety. Recording every temperature reading, every vaccine booster and every unusual behaviour in the same place prevents an important piece of information from being lost. This is exactly what a shared tracking record allows, where everyone sees what the others have observed and where vaccine and veterinary appointment reminders no longer slip through the cracks.
