About West Nile fever seasonal surveillance

The implementation of blood safety measures in the event of outbreaks of West Nile fever in humans is an important issue for the national competent authorities. According to the Commission Directive 2004/33/EC, efforts should be made to defer all blood donations from areas with ongoing transmission of West Nile virus (WNV) to humans to prevent its onward spread. A challenge to the implementation of the Directive is the timely collection of accurate information about areas with ongoing transmission. An important consequence of the deferral of blood donations from areas with West Nile fever is the impact on the blood supply for those areas.

The objective of this project is to inform the competent authorities responsible for blood safety of areas with ongoing transmission of West Nile virus to humans in order to support their implementation of blood safety legislation.

ECDC is providing, for the current transmission season, weekly updates on the reported cases of West Nile fever in humans in the EU Member States and neighbouring countries (i.e. those included in WHO European region and/or bordering the Mediterranean Sea). The updates are based on information obtained from the countries’ health authorities and refer to human autochthonous cases of West Nile fever only.

Definition of terms

West Nile fever is defined as probable and confirmed cases of West Nile virus (WNV) infection, as per case definition established in the Commission Decision 2008/426/EC. West Nile neuro-invasive infection only refers to the cases of West Nile fever presenting encepahlitis or meningitis.

In line with the West Nile virus preparedness plan in Europe:

  • an ‘affected area’ is defined as an ‘area with one or more autochthonous human WNV cases (neuro-invasive and non neuro-invasive), meeting laboratory criteria as per EU case definition’ (Directive 2008/426/EC);
  • the definition of an ‘affected area’ equals the definition of an ‘area with ongoing transmission of WNV to humans’, as used in Annex III of Commission Directive 2004/33/EC;
  • it is strongly recommended that at least the first case detected in an area should be confirmed according to the laboratory tests for case confirmation (Directive 2008/426/EC) and not only the laboratory tests for a probable case for the area to be determined as an ‘affected area’.

Legend: geographical scope and level

The weekly updated map shows in red the affected areas for the EU countries, and the areas reporting human cases, for the neighbouring countries.

The information is displayed at different spatial scales according to the countries’ reporting procedures.

  • For EU, EFTA and EU candidate countries, the displayed administrative levels correspond to NUTS 0, NUTS 2 or NUTS 3, as defined by EUROSTAT (the country, state/province/county and department/commune levels, respectively).
  • For the non-EU/EFTA countries, the Global Administrative Unit Layers (GAUL) are used. (GAUL disclaimer)

Areas where no case has been reported during the current year are coloured in dark grey. Countries not covered by the weekly updates are coloured in light grey.

Equine cases

In 2017 ECDC included in its epidemiological update data on equine cases. 

From 6 October 2017, ECDC publishes three types of West Nile fever maps: 1) human West Nile fever cases; 2) equine West Nile fever cases; 3) combined human and equine West Nile fever outbreaks. Human cases are collected through The European Surveillance System (TESSy) and equine outbreaks are collected through the Animal Disease Notification System (ADNS) of the European Commission. While the distribution of human cases covers EU/EEA countries and neighbouring countries, equine outbreaks are covering only EU/EEA countries.

Following a One Health approach, the new maps aim at highlighting areas, at NUTS3 level, where West Nile virus is circulating in incidental hosts. Currently, deferral or testing of prospective donors applies to blood donors leaving areas with one or more autochthonous human West Nile virus cases. This set of maps aims at better informing European Union Member States for the implementation of preventive measures.

Equine West Nile fever cases are defined according to the Terrestrial Animal Health Code of the World Organisation for Animal Health (OIE)