Tick-Borne Encephalitis Surge in France

Introduction

Tick-borne encephalitis (TBE), a notable arboviral infection transmitted through tick bites, has surged in France since its classification as a notifiable disease in May 2021.

Caused by the bite of infected ticks, the TBE has assumed critical importance in France following its designation as a notifiable disease in May 2021.

Understanding Tickborne Encephalitis (TBE)

Tickborne encephalitis (TBE) ranks among the most significant human arboviral infections affecting the central nervous system, with a stronghold in Europe and Russia^1,2. This disease primarily thrives in areas inhabited by transmission vectors, such as the Ixodes ricinus and I. persulcatus ticks. Over the last decade, TBE’s incidence has escalated, notably in regions like Lithuania, Germany, Switzerland, and Poland, with instances cropping up in new areas as well^3-5

Among the Tickborne encephalitis viruses (TBEV), which encompass dengue, yellow fever, West Nile, and Japanese encephalitis viruses, there exist three genotypes⁶: the European subtype transmitted by I. ricinus, and the Siberian and Far Eastern subtypes conveyed by I. persulcatus. Adult ixodid ticks rely on large mammals, such as goats, sheep, and cattle, as blood-feeding hosts, potentially leading to sporadic outbreaks through the consumption of raw milk from infected animals. It is noteworthy that Western Europe has hitherto experienced solely western genotype viruses. In central and Western Europe, TBE cases typically emerge from April to November, reaching a zenith in June–July and September–October, mirroring peak tick activity^1,2. The surge in TBE incidence is intricately linked to the burgeoning realms of tourism, trekking, and camping/hiking pursuits in regions endemic to the virus³. The European subtype of TBEV frequently engenders a biphasic ailment, characterized by an average incubation period of 7–14 days (with a range of 2–28 days). Primary infection often mimics flu-like symptoms, although asymptomatic cases are also prevalent (constituting 40% of cases). Notably, 5%–30% of clinical cases may manifest a secondary neurologic phase characterized by aseptic meningitis (in 50% of cases), meningoencephalitis (in 40% of cases), or meningoencephalomyelitis (in 10% of cases)^1,2,7,8. The Far Eastern subtype of TBEV is associated with more severe cases, including a mortality rate of 10%–20% and a higher incidence of neurologic sequelae (5%–30%)¹. Accurate diagnosis hinges on the detection of immunoglobulin M (IgM) antibodies in serum or cerebrospinal fluid (CSF), often determined using ELISA methods⁹. TBE garners 5–10 annual case reports in France, predominantly concentrated in the Alsace-Lorraine region since 1968 (2). However, a novel autochthonous case originating from the Aquitaine region in southwestern France has now been documented.

Surge in TBE Cases

As the curtain rose on the school summer holidays, Public Health France sounded an alarm regarding the escalating instances of locally acquired TBE infections within the country. Notably, mainland France has witnessed the proliferation of flavivirus, with the Auvergne-Rhône-Alpes region at the epicentre of a heightened viral circulation. Mountainous landscapes, including the Forez Massifs, stand particularly vulnerable to TBE transmission.

Disease Expansion: A Pan-European Concern

The geographical expanse of TBE incidence is extending its boundaries throughout Europe. Traditionally confined within certain areas and seasons, the virus transcends its historical limits, affecting regions with increasing breadth and duration. Notably, the Czech Republic, Germany, and the Baltic countries have encountered the brunt of this expansion.

Epidemiological Insights

The period between May 2021 and May 2023 has witnessed a surge in TBE cases, with a total of 71 instances reported by Public Health France. Within this timeframe, 30 cases surfaced in 2021, 36 in 2022, and five in 2023. An intriguing pattern emerges, with 37 out of the 71 cases transpiring between May and July. The demographic distribution of TBE cases reveals its impact across age groups, with four cases reported among children under 16 and 15 cases affecting individuals over 65.

Conclusion

In the face of the surging cases of tick-borne encephalitis in France, a clear message emerges: vigilance is paramount. The expanding reach of this disease underscores the need for heightened public awareness, protective measures, and potential vaccination strategies. As the battle against tick-borne illnesses intensifies, it is imperative that authorities, healthcare professionals, and individuals unite to mitigate its impact and secure a safer future.

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Reference

1. Dumpis U, Crook D, Oksi J. Tick-borne encephalitis. Clinical Infectious Diseases. 1999 Apr 1;28(4):882-90.
2. Hansmann Y, Gut JP, Remy V, Martinot M, Christmanna D. TBE virus infection: clinical and epidemiological data. Medecine et maladies infectieuses. 2004 Jun;34:S28-30.
3. Bröker M, Gniel D. New foci of tick-borne encephalitis virus in Europe: consequences for travellers from abroad. Travel medicine and infectious disease. 2003 Aug 1;1(3):181-4.
4. Skarpaas T, Ljøstad U, Sundøy A. First human cases of tickborne encephalitis, Norway. Emerging infectious diseases. 2004 Dec;10(12):2241.
5. Mansaray H, Durand JP, Reynes J, Bru JP. First human case of tickborne encephalitis in the area of Annecy, France. Jounées Nationales d’Infectiologie, Lille, France. Med Mal Infect. 2003;33:1-36.
6. Lefkowitz EJ. Taxonomy and classification of viruses. Manual of clinical microbiology. 2011 May 16:1262-75.
7. Gritsun TS, Lashkevich VA, Gould EA. Tick-borne encephalitis. Antiviral research. 2003 Jan 1;57(1-2):129-46.
8. Haglund M, Günther G. Tick-borne encephalitis—pathogenesis, clinical course and long-term follow-up. Vaccine. 2003 Apr 1;21:S11-8.
9. Holzmann H. Diagnosis of tick-borne encephalitis. Vaccine. 2003 Apr 1;21:S36-40.