West Nile Fever

Topics:

West Nile Fever (WNF) is a disease caused by the West Nile Virus. It belongs to a family of viruses called Flaviviridae, along with other viruses such as dengue and yellow fever. Although the reservoir of WNF is birds, the virus can be transmitted to humans via mosquitoes. WNF was first detected in the West Nile district of Uganda in 1937. The first large outbreak in Europe occurred in Romania in 1996. In Europe, cases have been identified in several countries including France, Italy and Portugal.

If notifiable disease is suspected, contact DAERA on 0300 200 7840 or your local DAERA Direct Regional Office. Failure to do so is an offence

Current Situation (Mar 2026)

The table below summarises the confirmed number of cases of West Nile Fever in equines in Europe since the beginning of January 2026

Country	Number of Cases
France	6
Italy	1
Portugal	14

Where is this disease found?

Ireland and the UK are currently free from West Nile Fever.

WNF has circulated in Europe since the 1950s. It is currently present in southern, eastern and western European countries. This presents a potential for spread across mainland Europe, towards the UK and Ireland. The virus has also been identified in the US. The transmission season during warmer months has also become longer in recent years, likely due to factors involved in climate change.

In 2022, nine European countries (Italy, Germany, Greece, Spain, Croatia, France, Hungary, Portugal, and Austria) reported 101 WNF outbreaks among equine species and 323 WNF outbreaks among birds. Portugal was the only one of these named countries which did not report any human cases of WNF in 2022.

In 2023, 709 locally acquired human cases of WNF (+19 travel associated), including 67 deaths were reported by 9 European countries (Italy, Greece, Romania, France, Hungary, Spain, Germany, Croatia, Cyprus). Cases occurred between 30/05/23-05/11/23, with the majority (96%) occurring between July and September. To date, the HPSC reported human travel related cases in Ireland in 2013 (1) and 2023 (1).

In 2024, the first human case of WNF was reported on 01/03/24 in Seville, Spain.

In 2025, there were 190 confirmed cases of WNF in Equines reported to the European Commission.

A map detailing countries affected with West Nile Fever is available here: West Nile fever (europa.eu)

Clinical signs

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.

What is the public health risk associated with this disease?

Humans can be affected by West Nile Fever, 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.

How is the disease transmitted?

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.

Prevention

Vaccination against the virus is available and is highly recommended for horses being transported abroad to areas where the virus is present. Humans, as well as horses, are encouraged to seek shelter from mosquitos where possible at peak times of the day, this could be providing mosquito nets in stables and humans wearing long sleeved tops and trousers. Avoiding travel to parts of the world which are at a higher risk of transmission, is also advisable.

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

What would happen if there was an outbreak of West Nile Fever in Northern Ireland?

West Nile Fever (WNF) is defined as a category E disease under EU legislation (Regulation (EU) 2018/1882). In the event of a case of WNF occurring in Northern Ireland, surveillance and notification to the EU are required. West Nile Fever is also a disease listed in the World Organisation for Animal Health (WOAH) Terrestrial Animal Health Code, and any outbreak must also be reported to WOAH. Ongoing surveillance programmes in wild or sentinel birds allow competent authorities of EU Member States to take appropriate protective control measures.

Control/Movement

In the event of a disease notification in Northern Ireland DAERA will restrict movement of horses under the following legislation, the Movement of Animals (Restrictions) Order (NI) 2004.

Anyone suspecting the presence of the disease, must immediately contact their Private Veterinary Practitioner (PVP) or inform their DAERA Direct Regional Office.