Epidemiological and Clinical Issues of Tick-Borne Encephalitis Virus Infection in Italy

Introduction TBEV (tick borne encephalitis virus) is endemic in certain areas of North Eastern Italy. The disease may occur in monophasic or biphasic course. TBEV infection cases without neurological symptoms (abortive TBE) are rarely reported. Methods We retrospectively analyzed all TBEV infection cases admitted to the Infectious Disease Unit of Belluno, a city of North Eastern Italy, between June 2000 and October 2018. Epidemiological and clinical data were recorded and statistically analyzed, in particular the relationship between morbidities and sequelae (neurological and not). Results We recorded 146 TBEV infection cases, 110 males and 36 females, mean age 53 years (range: 13-81). At first detection of serum antibodies, 141/146 cases presented TBEV IgG and IgM positive results, two cases only IgM positive results. Three cases were IgG and IgM negative at first, while positive later. Only 72 (51%) reported a previous tick bite. In four cases TBE-Lyme-coinfection occurred. 39/146 cases (27%) presented a monophasic course, 107/146 cases (73%) a biphasic course. Eight monophasic cases (5.5%) presented abortive TBE. Other rare clinical manifestations were observed: hiccups, bradycardia, urinary retention, temporary stuporous state, isolated persistent fever, fasciculations, clonia, divergent squint, hypotension, akinesia (0.7% each). 89 patients presented sequelae: 47 comorbid patients (28 with neurological sequelae) and 42 not comorbid (20 with neurological sequelae) (p>0.05), 66 cases with a biphasic course (62%) and 23 with a monophasic course (59%) (p>0.05). Neurological sequelae (48 cases) were: ataxia (16%), tremors (12%), depression (9%), paresthesias (6%), upper limb palsy (5.5%), lower limb palsy, amnesia, visual disorders (3% each), ideomotor slowing, urinary retention, concentration disorders, and hiccups (1.5% each). No one died because of TBEV infection. Conclusions According to our findings, TBEV infection may occur with several different clinical pictures and rare manifestations; association between neurological/not neurological sequelae and comorbidities is not present. In contrast with some previous studies, we observed a higher prevalence of abortive TBE (5.5%). In endemic areas of North Eastern Italy, even without a tick bite history and no neurological symptoms, TBEV infection has always to be considered as a possible diagnosis.