West Nile virus

West Nile virus is a mosquito-borne exotic disease that attacks a horse's brain and spinal cord. While it is not currently present in the UK, it is wide-spread across Europe and is expected to reach British shores in the near future, having already reached areas of France that border the English Channel. 

It is a notifiable disease in the UK, meaning that any suspected cases in England and Wales should be reported to Defra, and to the equivalent government authority in Scotland and Northern Ireland. 

How is it spread? 

West Nile virus is a vector-borne disease that reaches horses via birds and mosquitos in a three-stage process... 

1. Birds become infected with the disease while in warmer climates, then carry it to other countries during migration.
2. Mosquitoes bite the infected birds and become carriers themselves, able to pass it on to mammals including horses and humans.
3. An infected mosquito bites a horse or human, infecting them with the disease. 

West Nile virus can't be transferred between horses, or between horses and humans. The only way it can be transferred is through being bitten by an infected mosquito. 

clinical signs

Clinical signs of West Nile virus may include...

• Lack of energy
• Changes to behaviour
• Loss of coordination
• Weakness in limbs, leading to stumbling
• Muscle twitches
• Fever

Some horses are asymptomatic and won't show any signs of the disease, despite being bitten by an infected mosquito. 

Vaccination

The British Equine Veterinary Assocation (BEVA) and British Equestrian's Equine Infectious Disease Advisory group recommend that all horses travelling to Europe should be vaccinated against the disease. There are currently two licenced vaccines available in England, Scotland and Wales, and three for Northern Ireland. 

Depending on which one is used, the primary course is two vaccines administered into the neck, chest or gluteal muscles either three to five weeks apart or four to six weeks apart. The booster vaccine is then given on an annual basis. 

While West Nile virus is expected to reach the UK in the future, horses residing here who are not travelling abroad are not at risk and don't require vaccination at this time.

Prevention

In addition to vaccination, the best way to protect your horse from West Nile virus is to minimise their exposure to mosquitoes. This may include...

• Employing strict biosecurity principles – click here for advice
• Insect sprays and repellents – ensure these are safe for competition if you're competing
• Seeking shelter during peak times of the day – usually in the early evening
• Avoid areas of standing water, where mosquitoes breed
• Use fly rugs and other protective equipment
• Hang mosquito nets in stables

For further prevention strategies, speak to your vet for advice.