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With the arrival of autumn rains combined with temperatures exceeding 20°C, the proliferation of insects, particularly the Culex mosquito, increases, with an increase in its breeding sites.

This mosquito is the vector for transmission of the West Nile virus between birds (migratory and sedentary), which act as reservoirs for the virus.

Also, the mosquito harboring the virus transmits it by bite to humans, causing flu-like symptoms, and to other domestic mammals, including horses, causing fever and nervous disorders.

These accidental hosts are epidemiological dead ends for the disease and therefore do not contribute to the spread of the virus, and there is no transmission of the virus between humans or horses.

In Tunisia, West Nile fever has been diagnosed in humans and horses since 2003. In recent years, the disease has been confirmed by laboratories in humans and horses (the latest in 2024), with cases of mortality or sequelae of nervous system damage.

West Nile fever is a notifiable disease that does not place the horse in isolation or quarantine the stable.

How to recognize the disease

"My horse is behaving strangely" including:

- Ataxia (impaired coordination of movements) and locomotor difficulties that can lead to paralysis,

- Depression or, conversely, hyperexcitability, as in rabies, but without hypersalivation. This is why West Nile fever is often diagnosed in the laboratory after rabies is suspected,

- Muscle tremors,

- Hyperthermia (temperature > 38.5°C) and a decline in general condition.

Cases recover within 20 to 30 days, with sequelae that can persist for up to 6 months after infection.

How to combat this disease

The vaccine against this disease has proven effective in countries where it is marketed, which is not the case in Tunisia.

Other preventive measures are employed and consist of minimizing horses' contact with mosquitoes during high-risk periods (i.e., summer and autumn):

- Bring horses inside closed buildings before the end of the day and take them outside after dawn (i.e., outside periods of peak mosquito activity).

- Place mosquito nets at the entrances to stables.

- Natural or dynamic ventilation of stables,

- Avoid lighting the boxes and the stable,

- Install insect traps in stables and/or the surrounding environment and use larvicidal insecticides,

- Eliminate migratory bird nests, place chicken coops and ornamental birds away from stables,

- Use repellents on horses, while changing the molecules to prevent insect resistance.

- Limit stagnant water as much as possible (tarpaulins, ruts, trampling areas, flowerpots, tires, etc.).

- Clean water troughs regularly.

- Install a full, fine-mesh mosquito net cover impregnated with a repellent product.

With rising summer temperatures accompanied by high humidity during the day and night where the heat index (the sum of recorded temperature and humidity) exceeds 98, you should closely monitor your horse for the following warning signs of heat stress:

- rectal temperature above 39.5°C;

- rapid respiratory rate over 40 bpm, elevated heart rate over 60 bpm at rest;

- profuse or absent sweating;

- sudden fatigue, muscle tremors, dry gums with a filling time exceeding 3 seconds;

- dehydration with a skin fold that lasts more than 3 seconds.

- dark urine, prostration, loss of appetite.

Prevention is better than cure:

- Provide fresh water day and night, to which 30 to 60 g are added per day, and electrolytes by soaking hay or pellets.

- Showers and ventilation with misters are recommended, allowing for a rapid drop in body temperature. - Provide shaded and well-ventilated shelters, whether in a paddock or a stable.

- Avoid sporting activities between 10 a.m. and 4 p.m.

- Transport: a risk that increases the risk of heat stroke, and therefore, ensure maximum ventilation with stops every 1.5 hours, misting with water and electrolytes at each stop, and avoid journeys between 11 a.m. and 6 p.m.

At its recent in-person meeting, the FEI Board took the following Emergency Board Resolution: The following paragraph will be added to the FEI Veterinary Regulations, Article 1004 ‘Prohibited Methods’, for equine welfare reasons: “1004.4 It is strictly forbidden to use any type of substance/product inside or around the Horse’s mouth and/or tongue that may (i) imitate, induce or cause foaming; and/or (ii) coat or otherwise cover, or partially cover the bit. The prohibition excludes the use of products permitted in the FEI Tack App and the provision of permitted natural treats given in moderation. Contravening this rule will entail a Yellow Warning Card and Elimination.” This rule will come into effect on July 1, 2025.