Infectious Diseases

West Nile Virus (WNV)

What West Nile virus is, how it spreads, how to recognize it, and what you can do to prevent infection.

Updated: 1 min read

West Nile Virus (WNV)

Overview

West Nile virus (WNV) is a mosquito-borne flavivirus that cycles mainly between birds and mosquitoes. Humans and horses are dead-end hosts. Most infections cause no symptoms; some cause a flu-like illness; a small proportion develop neuroinvasive disease.

How it spreads

  • Vectors: Primarily Culex mosquitoes.
  • Reservoirs: Wild birds maintain the virus in nature.
  • Seasonality: Risk peaks in late summer and autumn.
  • Ecology: Warm, wet conditions (and sometimes drought clustering) amplify transmission.

Recognize symptoms

  • Most people: No symptoms.
  • Mild illness: Fever, headache, body/joint aches, fatigue, rash.
  • Severe (neuroinvasive): Severe headache, stiff neck, confusion, seizures, weakness or paralysis.

Seek urgent care for any neurological symptoms or rapidly worsening illness.

Prevention

  • Repellents: DEET, picaridin, or oil of lemon eucalyptus.
  • Clothing: Long sleeves/pants; socks/shoes at dusk/dawn.
  • Home: Install/repair screens; use bed nets where appropriate.
  • Environment: Remove standing water (gutters, pots, birdbaths); cover rain barrels.

Treatment

  • No specific antiviral.
  • Supportive care: Rest, hydration, fever/pain control.
  • Severe disease: Hospital-level care for complications.