Publié le 19 juin 2020

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The recent occurrence of an outbreak of tick-borne encephalitis (TBE) in the Oyonnax basin (Ain department)[1] first suggested the diagnosis of Covid-19. Indeed, the characteristic biphasic evolution of TBE starts with a flu-like syndrome (fever, fatigue, headaches and muscular pains) for 2 to 4 days, followed one to two weeks later by a second phase characterized by meningoencephalitis in a third of the patients. TBE is mainly transmitted by a tick of the genus Ixodes but, for the first time in France, this outbreak, which affected 26 people, recognizes a food origin (cheese made from raw goat’s milk).

With an average incidence of 20 cases per year, France is not “a “TBE” endemic region, apart from the reporting in 2016 of 54 cases in Alsace[2], but this zoonosis seems to be in a phase of recrudescence, as it is progressing significantly in the border countries (Switzerland, Germany).

With the summer season approaching, the increasing” scarcity of new cases of Covid-19 in France should broaden the differential diagnosis of influenza-like syndromes to include summer zoonotic infections (TBE, Q fever, Lyme disease, granulocytic anaplasmosis, tularemia, leptospirosis, hepatitis E, etc.), or not (enteroviruses, mycoplasmoses, chlamydioses).

Like TBE, several summer infections (Q fever, Lyme disease, anaplasmosis) are transmitted by a tick bite (in particular Ixodes ricinus)[3] which can sometimes inoculate several pathogens simultaneously. The survey carried out since 2017 via the « Signalement Tiques” (“Tick Report ») application shows that tick bites are not limited to forest excursions, that they occur in a third of the cases in private gardens and public parks and that reports have doubled compared to previous years, with 2020 appearing to be a year where ticks are particularly active.

Maintaining the vigilance necessary for the epidemiological surveillance of Covid-19 should not overshadow the summer flu-like syndromes. This is why the National Academy of Medicine and the Veterinary Academy of France recommend :

– to systematically resort to laboratory diagnosis (RT-PCR supplemented by serology) before any clinical suspicion of a Covid-19;

– in the “case” plutôt que event of repeated negativity of the Covid-19 diagnostic tests, to “consider” plutôt que refer to a zoonotic infection in the event of any summer flu syndrome, particularly when there is an outbreak of several infected persons in a tick-rich region;

– to prevent tick bites by applying the usual recommendations for “forest walks” plutôt que in the forest, but also in gardens and public parks.



[1] Brugère-Picoux J. Tick-borne encephalitis: an emerging ancient zoonosis? First description of a foodborne outbreak in France. La dépêche vétérinaire, 2020, n°1532, 13 June.

[2] Velay A. A new hot spot for tick-borne encephalitis (TBE): A marked increase of TBE cases in France in 2016. Ticks and Tick-borne Diseases, 2018, 9, 120-125;

[3] George JC, Chastel C. Summer flu syndromes and tick-borne infections Ixodes ricinus. Spectra biol. 2004, 142: 30 – 37.