Abstract
North-eastern Poland is an endemic region for tick-borne encephalitis (TBE). The COVID-19 pandemic overlapped with the activity period of ticks that are the main vectors for TBE. As we know from short observation worldwide, SARS-CoV-2 virus affects significantly the immune system and can lead to serious complications of other infections even in previously healthy patients. A 24-year-old female patient, who lived close to the forest, was admitted to the Department of Neurology at Medical University of Bialystok with fever, dizziness, and progressive left-sided hemiparesis for three days. She had no medical history of chronic disease and was not vaccinated against TBE. The patient had SARS-CoV-2 infection three weeks prior to admission to the hospital (positive IgG against SARS-CoV-2). During COVID-19 infection she had fever, myalgia, a mild dyspnoea without indications for oxygen therapy and recovered after one week. During hospitalisation in the Department of Neurology the patient presented neck stiffness, progressing tetraparesis, dysarthria and weakness of the neck muscles. The magnetic resonance of the head revealed numerous lesions, mainly in both thalamus, longitudinal lesion was found in the cervical spinal cord. The cerebrospinal fluid analysis indicated lymphocytic inflammation. A high level of TBE antibodies in both serum and CSF was found. After immunoglobulin and symptomatic treatment her condition gradually improved. The recovery after SARS-CoV-2 infection overlapping with TBE might have influenced the course of tick-borne disease in a bad manner. The correct diagnosis can be a challenge as COVID-19 can lead to further complications, also neurological. The co-incidence we observed is very rare, however during the pandemic it is pivotal to remember about possible occurrence of other infections and their atypical course.