Cases of encephalitis of varying severity have been described in recent years in eastern France involving tick-borne encephalitis virus (TBEV). The main objective is to demonstrate the presence of TBEV in Limousin, in patients with a positive Lyme serology, or a neurological picture compatible with TBEV.

Cases of encephalitis of varying severity have been described in recent years in eastern France involving tick-borne encephalitis virus (TBEV). The epidemiological situation in France is poorly known with about 20 cases diagnosed per year, mainly in Alsace and Haute-Savoie. The infection can result in fever and an influenza-like picture, which can be complicated by encephalitis-like neurological disorders, or even death. TBEV is transmitted by the tick Ixodes ricinus, which also carries Borrelia burgdorferi, the agent of Lyme disease. Limousin is one of the French regions with the highest prevalence of Lyme disease. These ticks can harbor various pathogens, including TBEV. A case was described in 2007 in Bordeaux. More recently, a case was described in Haute-Loire. The investigators are therefore interested today in the emergence of this virus in Limousin following a possible progression through the Massif Central, potentially favored by numerous anti-Covid-19 control containments. The study begins with a computer extraction of patients with Lyme serology from our GLIMS laboratory software (with positive or negative results), a check for non-oppositions. Then the investigators will measure by ELISA in microplates the anti-TBEV IgG as well as the anti-TBEV IgM on the sera + in TBEV IgG. The investigators will then send a patient questionnaire with an information note to document the context of this TBEV seropositivity and to eliminate false-positivities (vaccination). Finally, the investigators will perform PCR on CSF if serum positive and CSF available, followed by an analysis of results.

Inclusion Criteria:

• Patient with Lyme serology. Neurological picture compatible with neuroborreliosis or encephalitis.
• No objection from the patient to the use of biobank samples

Exclusion Criteria:

• Patient's opposition.

patients with Lyme serology from our GLIMS laboratory software (with positive or negative results)