TBE in France

Abstract

The first human case of tick-borne encephalitis virus (TBEV) infection in France was reported in 1968 in Alsace, an eastern region next to the German border: a gamekeeper working in a forest near Strasbourg. Between 1970 and 1974, an extensive research survey confirmed the presence of TBEV in ticks and rodents in this French region. Eight percent of adult tick batches collected were infected (I. ricinus) by the TBEV. Tick collection occurred in a forest near Strasbourg, the main city in the region. Nymphs were more rarely infected (1.6% of the collected lots). These data were confirmed in 2011 in Alsace in Guebwiller’s Valley, a middle altitude forest, with identification of western (European) subtype TBEV (TBEV-EU). The infection rate still remains low: TBEV was detected only in the I. ricinus nymphs (2.48%) that were collected during May; however, not in those collected during the other spring or summer months. In a more recent study, Bestehorn et al., collected ticks (953 male, 856 female adult ticks and 2,255 nymphs) in endemic foci in the upper Rhine region in France and Germany between 2016, 2017 and 2018 by flagging. The minimal infection rate (MIR) of the collected ticks in the Foret de la Robertsau (France) was estimated to 0,11% (1 nymph/944 ticks). The isolated and sequenced TBEV strain from Foret de la Robertsau (F) is related to circulating TBEV isolates from eastern Bavaria and the Czech Republic. In the French department Alsace, there are today at least two independent TBEV strains circulating: the historical Alsace strain isolated in 1971 and the newly identified strain from Foret de la Robertsau. Other wooded regions (Ardennes) were explored for TBEV in ticks, but without evidence of virus infection.