Retrospective Study of Tick Bites Associated with Neurological Disease in a Level Three University Hospital in Switzerland

Background: Ticks represent very important vectors of human and zoonotic pathogens, and tick-borne diseases (TBDs) are diagnosed with increasing frequency. Therefore, the aim of this retrospective study was to describe patients presenting with a complaint of tick bite in the emergency department (ED) of a large university hospital in Switzerland.

Methods: Data were collected by searching for keywords in the routine clinic database to identify cases from 1 July 2012 to 30 June 2020. The patients' data were screened for preexisting diseases and demographic and clinical characteristics.

Results: We included 415 patients collected over a period of 8 years, with highest admission frequencies from May to July. Of these, 82% were outpatients, 15.9% admitted to a hospital ward, and five to intensive care. The patients were allocated to three groups. The first group represented patients with erythema chronica migrans (ECM), which is pathognomonic for Lyme borreliosis (n = 45). Accordingly, 89% of cases in this group of patients were treated with antibiotics. The second group represented patients with other tick bite-associated erythema (n = 139). In this group, no particular clinical symptoms or laboratory findings were found. Finally, the largest group represented patients in which the tick bite was no longer visible (n = 201). This group of patients had significantly more evidence of neurological disorders (52%) and were treated at a higher rate with non-steroidal anti-inflammatory (29%) or antiviral (13%) drugs. Although the vaccination status for tick-borne encephalitis virus (TBEV) was not systematically evaluated, at least 10% of the latter group was vaccinated, indicating another source for neurological disease. Furthermore, only 14% of the tested patients were positive for IgM or IgG against TBEV.

Conclusion: This retrospective study indicates the presence of many undiagnosed neurological diseases following tick bites that could be caused by TBEV or an unknown infectious agent. Taken together, although tick bites were not very frequently seen in the present tertiary ED, the frequent presence of neurological symptoms demands a more systematic assessment of vaccination status and TBEV serology as well as further diagnostic evaluations in patients that report tick bites and neurological symptoms.