Tick-Borne Encephalitis Cases Increasing in France

FRANCE — Since becoming a notifiable disease in May 2021, tick-borne encephalitis (TBE), which is transmitted through the bite of an infected tick, has been closely monitored, with case numbers being recorded as a way of documenting its spread. 

At the start of the school summer holidays, Public Health France warned that the number of locally acquired (in France) TBE infections is on the rise. 

Flavivirus is spreading in mainland France, and the Auvergne-Rhône-Alpes region is now seeing high rates of circulation of the virus, with mountainous regions like the Forez Massifs being particularly at risk. 

The incidence of the disease is also increasing throughout Europe with the area and season in which the virus usually circulates becoming wider and longer. The countries most affected are the Czech Republic, Germany, and the Baltic countries. 

Gaining Ground

Seventy-one cases were reported by Public Health France between May 2021 and May 2023: 30 in 2021, 36 in 2022, and five in 2023. In the 2 years overall, 37 cases out of the 71 reported occurred between the months of May and July. 

Of the 71 cases reported, four related to children under age 16, and 15 were in the over-65s. 

In 86% of cases (61 people), the infection was acquired in France. The other cases had been infected in an “at-risk” country and occurred in people who had been traveling or French citizens routinely residing in one of these “at risk” countries. 

In 62% of cases, the departments in which these locally acquired infections occurred were known at-risk areas before the start of monitoring via the mandatory notification declaration. The departments include Haute-Savoie (14 cases), Haut-Rhin (11), Bas-Rhin (10), Loire (3), Ain (2), Puy de Dôme (2), Isère (1), and Savoie (1). Experts at Public Health France commented that “Haute-Savoie is the department that has reported the most cases over the last 2 years, while the recognition of the virus there is much more recent than in Alsace.” 

Sixteen people were infected in departments deemed infection-free up to that point: Rhône (4), Ardèche (2), Cantal (2), Doubs (2), Vosges (2), Meurthe et Moselle (1), Marne (1), Moselle (1), and Haute Saône (1). In one case there was uncertainty as to where the infection had been acquired; Meurthe-et-Moselle or Vosges. This means that this arthropod-borne virus has spread as far as the southern Ardèche region; according to Public Health France, “extra caution should be taken in this department.” 

Infections caused by tick-borne encephalitis are spread by ticks and, more rarely, by consumption of raw milk products from recently infected livestock. In its report, Public Health France indicated that 11 of the cases were in people exposed to tick bites through work activities (stock breeders, horticulturists, forest rangers, etc) and that 36 cases reported a bite compatible with the onset of the first symptoms. Eighteen cases reported consumption of raw milk products. 

Ninety-Four Percent Hospitalization Rate

After a one- to two-week incubation period, tick-borne encephalitis begins suddenly, like influenza, with fever, headache, and chills. Forty percent of people infected may experience long-term neurological effects lasting several years. 

Thirty-seven percent of cases declared between May 2021 and May 2023 presented with meningitis, 38% encephalitis, 13% meningoencephalitis, and 3% encephalomyelitis. Ten percent had no neurological signs. 

Ninety-four percent of cases required admission to hospital. There were no deaths. 

Although vaccination is not yet recommended in France, Public Health France warns that the public should protect itself from tick bites and carefully inspect their body and that of their children after walking in rural areas or woodlands in endemic regions of up to 1500 meters altitude, between spring and autumn. 

This article was translated from Medscape’s French edition.

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