International Journal of Medical Microbiology
Identification of new endemic tick-borne encephalitis foci in Poland – a pilot seroprevalence study in selected regions
Introduction
Central European tick-borne encephalitis (TBE) is a viral disease of the central nervous system, which persists endemically in several Central-European countries (Dumpis et al., 1999). Although the main route of transmission of tick-borne encephalitis virus (TBEV) is through tick bites, TBE outbreaks were linked to the consumption of raw milk (Matuszczyk et al., 1997; Kerbo et al., 2005). TBE is a mandatory reportable disease in Poland since 1970. The administrative division of Poland and the geographic distribution of registered TBE incidence per 100,000 inhabitants in 1994–2005 are presented in Fig. 1. The routine surveillance data indicate clustering of TBE incidence in two north-eastern voivodships, Podlaskie and Warminsko-mazurskie, and only sporadic case reports from isolated districts in other voivodships (Fig. 1b). Before the introduction of the mandatory surveillance, large-scale serologic surveys were performed in 1965–1972 among more than 20,000 foresters and 17,000 other subjects representing the general population (Wroblewska et al., 1968, Wroblewska et al., 1973). Antibodies against TBEV detected using the hemagglutination inhibition test were found in 0.5–6.5% of the population and in 7.0–27.0% of the foresters in different regions. Regions with a particularly high prevalence of antibodies against TBEV have been identified, including areas in the northern and eastern parts of Poland (Fig. 2). Further evidence on the presence of active TBE foci was provided by virological studies of ticks in selected regions and regional seroprevalence studies (Prokopowicz et al., 1995; Cisak et al., 1998, Cisak et al., 2002). In these studies, evidence on the presence of active foci in the Pomorskie, Podlaskie, and Lubelskie voivodships was strengthened. In general, the extent of the disease incidence as notified within the surveillance system is not compatible with the seroprevalence distribution established in field studies.
The aim of the present study was to perform a serologic survey among humans assessing the prevalence of antibodies against TBEV in selected regions of Poland classified as endemic and non-endemic. Additional objective evidence of the endemic status of selected regions was obtained from a parallel serologic survey among goats.
Section snippets
Materials and methods
The present seroprevalence study among humans was based on serum samples (n=1498) selected from a serum bank collected by the Dept. of Virology, National Institute of Public Health, in 1996–2005. The samples were obtained from subjects referred to local health departments for testing against different pathogens not related to neuroinfections, including HBV, food-borne pathogens, etc. A stratified sample without replacement, weighted on age group, gender, and geographic location was selected
Results
Out of 1498 human samples tested, 39 were positive for anti-TBEV antibodies, giving an overall seroprevalence of 2.6%. Out of 38 re-tested samples, 35 were confirmed with TBEV-specific tests. However, only 7 out of the 10 re-tested sera from Podlaskie voivodship, 3/10 from Kujawsko-Pomorskie, 1/5 from Pomorskie, and merely 4 out of the 14 tested sera from the remaining voivodships (Lubelskie, Zachodniopomorskie, Wielkopolskie, Dolnośląskie) indicated earlier infection based on IIF and HI
Discussion
The present study explored the possible existence of TBE endemic foci in regions of Poland considered free of disease based on information provided by the routine communicable disease surveillance system. The results of this pilot survey indicate that altogether as many inhabitants of non-endemic regions as inhabitants of endemic regions were exposed to TBE virus. In the 4 north-western non-endemic voivodships, where the TBEV antibody prevalence was >1%, only sporadic cases were reported during
Acknowledgements
This work has been funded by Med-Vet-Net, Workpackage 31. Med-Vet-Net is an EU-funded Network of Excellence (FOOD-CT-2004-506122).
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2020, Journal of Clinical Medicine