Epidemiological update: West Nile virus transmission season in Europe, 2018

Human cases

In the 2018 transmission season a higher number of cases were reported compared with transmission seasons in previous years. As of 13 December 2018, 1 503 human cases were reported in the EU/EEA by Italy (576), Greece (311), Romania (277), Hungary (215), Croatia (53), France (27), Austria (20), Bulgaria (15), the Czech Republic (5), Slovenia (3) and Cyprus (1). In the EU neighbouring countries 580 human cases were reported by Serbia (415), Israel (128), Turkey (23) and Kosovo* (14). Hundred-eighty deaths due to West Nile virus infection have been reported by Greece (47), Italy (46), Romania (43), Serbia (35), Kosovo* (3), Turkey (3), Bulgaria (2), the Czech Republic (1) and Hungary (1).

In 2018, the first cases in the European Union (EU) were notified by Greece in week 26 (25 June to 1 July), with the earliest disease onset on 31 May (week 22). In the EU neighbouring countries the first case was reported by Serbia with a date of onset from week 24.

The last case of this transmission season in the EU was reported by France at the end of November, with a date of onset from week 46. This represents an unusually late date of onset since in past transmission seasons in the EU/EEA and EU neighbouring countries, the latest date of onset typically occurred between weeks 39 and 42.The latest date of onset in the EU neighbouring countries this transmission season was reported by Turkey from week 39 (24 to 30 September).

The total number of reported autochthonous infections in 2018 (n= 2 083) exceeds, by far, the total number from the previous seven years (n= 1 832).Compared to the previous transmission season in 2017, there was a 7.2-fold increase. The highest increase compared to the previous transmission season was observed in Bulgaria (15-fold) followed by France (13.5-fold) and Italy (10.9). The case fatality ratio (CFR) among the symptomatic cases in 2018 has not exceeded the CFR of the previous two years (9% in 2018 compared with 11% in 2017 and 9% in 2016). The proportion of cases with West Nile neuroinvasive disease (WNND) among symptomatic cases is comparable to the previous two years (68% in 2018 compared with 73% in 2017 and 65% in 2016).

All mosquito-borne autochthonous human cases during the current transmission season were reported in previously affected countries. As in previous years, the virus spread to NUTS 3 areas where no human autochthonous cases had been reported before.

Equine cases

During the 2018 transmission season, 285 West Nile fever outbreaks among equids were reported by EU Member States through the Animal Disease Notification System: 149 in Italy, 91 in Hungary, 15 in Greece, 13 in France, 9 in Spain, 2 in Austria, 2 in Romania, 2 in Germany, 1 in Slovenia and 1 in Portugal. This is a 30% increase compared to number of outbreaks in 2017.