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. 2024 Feb 13;12(2):386.
doi: 10.3390/microorganisms12020386.

An Overview of Tick-Borne Encephalitis Epidemiology in Endemic Regions of Continental Croatia, 2017-2023

Tatjana Vilibic-Cavlek  1   2 , Stjepan Krcmar  3 , Maja Bogdanic  1 , Morana Tomljenovic  4   5 , Ljubo Barbic  6 , Dobrica Roncevic  4   7 , Dario Sabadi  8   9 , Marko Vucelja  10 , Marija Santini  2   11 , Blazenka Hunjak  12   13 , Vladimir Stevanovic  6 , Marko Boljfetic  10 , Linda Bjedov  10 , Viktor Masovic  6 , Tanja Potocnik-Hunjadi  14 , Danijela Lakoseljac  4   7 , Mahmoud Al-Mufleh  15 , Vladimir Savic  16
Affiliations

An Overview of Tick-Borne Encephalitis Epidemiology in Endemic Regions of Continental Croatia, 2017-2023

Tatjana Vilibic-Cavlek et al. Microorganisms. .

Abstract

Tick-borne encephalitis (TBE) represents an important public health problem in Europe. We analyzed the epidemiology of TBE based on data from humans, animals, and Ixodes ricinus ticks in endemic regions of continental Croatia. In the period from 2017 to 2023, cerebrospinal fluid (CSF) and serum samples of 684 patients with neuroinvasive diseases, 2240 horse serum samples, and 300 sheep serum samples were tested for TBEV. In addition, 8751 I. ricinus ticks were collected. CSF samples were tested using RT-PCR. Serological tests (serum, CSF) were performed using commercial ELISA, with confirmation of cross-reactive samples by a virus neutralization test. Eighty-four autochthonous human TBEV cases were confirmed. The majority of patients were in the age group of 40-69 years (58.3%) with a male predominance (70.2%). TBE showed a bimodal seasonality with a large peak in April-August and a small one in October-November. In addition to humans, TBEV IgG antibodies were found in 12.2% of horses and 9.7% of sheep. Seasonal tick abundance corresponds to the reported number of human infections. Continental Croatia is still an active natural focus of TBE. Continuous monitoring of infections in humans, sentinel animals, and ticks is needed for the implementation of preventive measures.

Keywords: Croatia; Ixodes ricinus; epidemiology; tick-borne encephalitis virus.

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Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of this study; in the collection, analyses, or interpretation of data; in the writing of this manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Sampling areas of Ixodes ricinus ticks in Continental and Alpine regions of Croatia by year (numbers represent county labels).
Figure 2
Figure 2
Sampling timeline in humans, animals, and ticks, 2017–2023.
Figure 3
Figure 3
Geographic distribution of the study participants: sampling area (red-shadowed) with county labels (left) and number of participants by county (right).
Figure 4
Figure 4
Seasonal distribution of tick-borne encephalitis in Croatia, 2017–2023.
Figure 5
Figure 5
Geographic distribution of acute tick-borne encephalitis cases in Croatia, 2017–2023 (left); IgG-seropositive participants (right).
Figure 6
Figure 6
Age and gender distribution of patients with tick-borne encephalitis in Croatia, 2017–2023.
Figure 7
Figure 7
Distribution of patients with tick-borne encephalitis in Croatia according to clinical presentation, 2017–2023.
Figure 8
Figure 8
Seasonal distribution of Ixodes ricinus ticks, 2017–2023.
Figure 9
Figure 9
Geographic distribution of tick-borne encephalitis IgG-seropositive horses, 2017–2020. The colors represent seroprevalence rates (%).
Figure 10
Figure 10
Distribution of tick-borne encephalitis virus IgG-seropositive sheep, 2022. Seroprevalence rates (%) are presented for three locations: Trpinja (1), Borovo (2), and Vukovar (3).
See this image and copyright information in PMC

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