West Nile Protection for Horses by a Vet – 2025 Vaccine, Symptoms & Mosquito Control Guide 🦟🐴

By Dr Duncan Houston, BVSc

Introduction

West Nile Virus (WNV) continues to be one of the most dangerous mosquito-borne diseases affecting horses in the United States. Although it's no longer making daily headlines, this virus is now endemic—meaning it's permanently present across the country. In 2025, vaccination and mosquito control remain essential tools for protecting equine health, especially during the summer and fall months.

What Is West Nile Virus? 🦠

• A mosquito-borne flavivirus
• Infects birds as the primary host
• Transmitted to horses and humans via mosquito bites
• Now considered endemic across the U.S.

How Dangerous Is West Nile for Horses? 🚨

• 30–40% mortality rate in confirmed cases
• 40% of survivors may have lasting neurological signs months after recovery
• High cost of treatment and extended recovery periods

Symptoms of West Nile Virus in Horses ⚠️

• Neurological signs including:
  • Depression or lethargy
  • Muscle twitching
  • Weakness in the legs
  • Uncoordinated movement (ataxia)
  • Partial paralysis
  • Inability to stand

Diagnosis

• Requires specific blood testing
• Some tests may give false positives if the horse has been vaccinated
• Your vet will recommend the appropriate test to distinguish vaccination from true infection

Vaccination: Your Best Defense 💉

• All horses should be vaccinated against West Nile virus
• Initial series: two doses, 3–6 weeks apart
• Booster: annually, or twice yearly in high-risk areas
• Work with your vet to determine ideal booster schedule based on geography and exposure risk

Seasonal Risk 🌦️

• Risk increases in late summer and early fall
• Horses should receive their boosters in spring to provide full protection during peak mosquito season

Mosquito Control Measures 🦟

• Eliminate standing water around barns and paddocks
• Use equine-safe repellents on horses
• Install mosquito netting and use fans in stalls to disrupt mosquito flight
• Encourage natural predators like swallows and bats

Case Example: Late Vaccination and WNV in a Gelding

1. 12-year-old gelding in Texas was late receiving his spring booster
2. Developed muscle tremors and ataxia