West Nile fever: how to spot and report the disease

How to spot West Nile fever, what to do if you suspect it and measures to prevent its spread.

Applies to England, Scotland and Wales

West Nile fever affects a variety of animals including but not limited to:

  • horses
  • birds
  • humans

West Nile fever is a notifiable animal disease. If you suspect it you must report it immediately by calling the Defra Rural Services Helpline on 03000 200 301. In Wales, contact 0300 303 8268. In Scotland, contact your local Field Services Office. Failure to do so is an offence.

How to spot West Nile fever

In horses clinical signs can include:

  • lack of energy
  • loss of coordination
  • weakness in limbs leading to stumbling

Some horses will not show any signs at all.

Birds are the main carrier of West Nile fever, but not all species show signs of the disease.

Risk to humans from West Nile virus

Humans can be affected by West Nile virus, although often the infection does not lead to any symptoms. If present, the most common symptoms are a flu-like illness.

Most mild infections resolve in a few days. A more severe disease develops in less than 1% of cases.

See Public Health England information about West Nile virus in the UK.

You can read more about West Nile virus in humans at NHS Choices.

How West Nile fever is spread

The disease is spread by mosquitoes. It is not spread directly between animals.

Birds are the most common carriers and may spread West Nile fever between countries when they migrate.

Preventing and controlling West Nile fever

You can help prevent the disease by practising strict biosecurity on your premises.

If you report suspicion of West Nile fever, APHA vets will investigate.

If the disease is confirmed it will be controlled in line with the contingency plan for exotic notifiable diseases.

Further information on prevention and control

Controls to prevent disease

What happens when a notifiable disease is suspected or confirmed

Legislation on West Nile fever

The main legislation relating to control of West Nile fever is the Infectious Diseases of Horses Order 1987.

Published 26 August 2014
Last updated 18 October 2018 + show all updates
  1. Contact details for reporting a notifiable disease updated.

  2. Updated 'risk to humans from West Nile virus' section and linked to Public Health England guidance

  3. AHVLA documents have been re-assigned to the new Animal and Plant Health Agency (APHA).

  4. First published.