Epidemiological update: West Nile virus transmission season in Europe, 2020

Epidemiological update

As of 1 February 2021, European Union (EU) and European Economic Area (EEA) Member States and EU-neighbouring countries reported 336 locally-acquired human cases of West Nile virus infections in 2020. The last case of this transmission season was reported by the Netherlands in week 47.

Human infections

As of 1 February 2021, European Union (EU) and European Economic Area (EEA) Member States and EU-neighbouring countries reported 336 locally-acquired human cases of West Nile virus (WNV) infections in 2020.

EU/EEA Member States reported 316 locally-acquired human cases of WNV infection with known place of infection, including 38 deaths, through The European Surveillance System (TESSy). Cases were reported by Greece (143), Spain (77), Italy (66), Germany (13), the Netherlands (7), Romania (6), Hungary (3) and Bulgaria (1). Deaths were reported by Greece (23), Spain (8), Italy (5), Romania (1) and Bulgaria (1).

The province of Pazardzhik in Bulgaria, the province of Badajoz in Spain, the regions of Utrecht and Arnhem/Nijmegen in the Netherlands and five regions in Germany (Barnim, Ostprignitz-Ruppin, Saalekreis, Halle (Saale) and Meissen) reported locally-acquired human cases of WNV infection for the first time. All other cases reported through TESSy were reported from areas that had been affected during previous transmission seasons. Three locally-acquired cases were reported without place of infection, by Germany, Greece and Italy.

Two travel-related cases of WNV infection were reported this transmission season, one associated with travel to Greece and one with unknown place of infection.

EU-neighbouring countries reported 17 human cases of WNV infection; all were reported by Israel.

In 2020, the first case in the EU was notified by Romania in week 25 (15 to 21 June), with disease onset in week 23 (1 to 7 June). The last case was reported by the Netherlands in week 47 (16 to 22 November), with disease onset in week 43 (19 to 25 October).

During this transmission season, the Netherlands reported their first detection of a WNV infection in a bird and subsequently the first detection of human cases of WNV infection. This corroborates the further expansion of WNV circulation in Europe. All other human infections in 2020 were reported in countries with known persistent transmission in previous years.

Animal outbreaks

Since September 2019, ECDC started to include West Nile virus infections among birds in addition to human and equine infections in its epidemiological updates. Animal data (including outbreaks among equids and birds) are collected through the Animal Disease Notification System (ADNS) of the European Commission. While the report of equine encephalomyelitis due to WNV is mandatory at the EU level, the report of WNV infections among birds is voluntary. The distribution of human cases covers EU/EEA Member States and EU neighbouring countries, whereas outbreaks among equids and birds cover only EU/EEA Member States.

During the 2020 transmission season, 183 outbreaks among equids were reported by EU/ EEA Member States through ADNS. These outbreaks were reported by Spain (133), Germany (23), Italy (16), France (5), Portugal (2), Austria (2), Greece (1) and Hungary (1). In addition, two outbreaks among birds were reported through ADNS, both by Bulgaria.

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