Tickborne Encephalitis Virus, Northeastern Italy

Abstract

To the Editor: Approximately 3,000 cases of tickborne encephalitis virus (TBEV) disease are registered annually in Europe (1). In Italy, indigenous TBEV infection cases have been only sporadically recorded from 1975 through 2001; in addition, serologic investigations in populations at risk in northern Italy have shown only a low prevalence of specific antibodies (0.6%–5%) (2,3). A surveillance system for TBEV infections was started after autochthonous TBEV was recognized in late summer and fall 2003 in Friuli-Venezia Giulia (FVG), a small region of northeastern Italy with nearly 1 million inhabitants (4). Surveillance is based on systematic microbiologic screening of all patients referred to the emergency departments of regional hospitals for suspected community-acquired central nervous system infections or fever and headache with a history of tick bite in the past 6 weeks. Screening for TBEV was performed on sera or cerebrospinal fluid (CSF) by enzyme immunoassay (Enzygnost Anti-TBE virus Ig, Dade Behring Marburg GmbH, Marburg, Germany) and repeated on convalescent-phase sera. Demonstration of specific immunoglobulin M (IgM) in serum or CSF in the acute phase or >4-fold rise in serum antibody titer in the convalescent phase was interpreted as an indicator of recent TBEV infection. For surveillance purposes, TBEV infection was defined when hemagglutination-inhibition antibody test and neutralization assay by a reference laboratory confirmed ELISA results (5). Data were collected at a regional reference center, where cases were classified as possible, probable, and confirmed, according to the new TBEV case definition (6). From July 2003 through November 2005, 20 cases of TBEV infection were detected; their demographic, epidemiologic, and clinical characteristics are given in the Table. Cases occurred throughout the year, with a biphasic peak in June and September–November. A biphasic clinical course was reported in 10 patients. The median period between tick bite and date of referral to hospital was 22 days (range 15–46 days). Seventeen cases were classified as confirmed, 2 as probable, and 1 case could not be classified because symptoms started after tick season (December) (6). Two patients were coinfected with Borrelia burgdorferi. Table Demographic, epidemiologic, and clinical data of 20 patients with TBEV infection in Friuli-Venezia Giulia* The most common symptoms were fever, headache, nausea, vomiting, and myalgia; the most common central nervous system signs were stiff neck, irritability, and limb paresis. Five patients only reported headache and fever without neurologic signs. Lumbar puncture, performed in 15 patients, showed mild pleocytosis with neutrophil predominance in 13 patients, elevated protein level in 14 patients, and normal glucose level in all. The clinical syndrome was classified, in accordance with Kaiser et al., into febrile form (4 cases), aseptic meningitis (3 cases), encephalitis (2 cases), meningoencephalitis (8 cases), and meningoencephalomyelitis (3 cases) (7). None of the patients died, but 3 required respiratory support in the intensive care unit. Outcome was favorable for 9 patients; major neurologic sequelae were observed in 6 and minor sequelae in 5. During the past 20 years, TBEV has reemerged in several European areas that had been disease free (1,8). In FVG, which borders disease-endemic areas such as Slovenia and Austria, the first cases of TBEV infection were documented recently (4). Several explanations, in addition to the well-established role of climate change, can be proposed (1). First, in Slovenia, after the end of the Communist regime, recreational activities increased considerably, with the creation of natural parks and hunting grounds, densely populated with deer, chamois, rodents, foxes, and other wild animals that can easily cross national borders (9). Second, after the 1976 earthquake that destroyed a large number of mountain villages in FVG, economic activities were progressively concentrated in the plains of the region, which rapidly increased urbanization of the plains towns. As a consequence, the mountains in the northern part of the region were progressively abandoned by humans and returned to wilderness. A final possible explanation is that TBEV cases were undiagnosed because awareness among local physicians was low; however, this variable likely played a minor role, since a recent serologic survey of persons at high risk (forest rangers) yielded a low positivity ratio (3). If even workers at risk had a low seroprevalence, TBEV cases were likely uncommon in the region. The implementation of a regional active surveillance system allows the highest sensitivity in assessing the epidemiologic features of TBEV infections, which are characterized by highly disease-endemic microfoci in areas free of the problem (10). Precisely defining areas where risk is particularly will lead to optimal use of prevention programs and design of educational programs for residents, tourists, and healthcare workers.