Tick-borne encephalitis: A 43-year summary of epidemiological and clinical data from Latvia (1973 to 2016).

Dace Zavadska,Angelika Krumina,Linda Bridina,Guntis Karelis,Lelde Liepina,Heinz-Josef Schmitt,Wilhelm Erber,Jelena Storozenko,Antra Bormane,Jurijs Perevoscikovs,Irina Lucenko,Laura Veide,Myint Tin Tin Htar,Zane Anna Litauniece,Zane Odzelevica

doi:10.1371/journal.pone.0204844

Abstract

BackgroundThe incidence of tick-borne encephalitis (TBE) varies significantly over time. To better understand the annual incidence of all TBE cases in Latvia we investigated the disease burden in the country from 1973–2016 using several available sources and case definitions.MethodsWe identified cases of TBE from an electronic database (maintained by the Centre for Disease Prevention and Control of Latvia [CDPC]) by the use of ICD-10 diagnosis codes for TBE (A84; A84.0; A84.1; A84.8; A84.9). In addition, previously unreported TBE cases were found by review of TBE diagnoses according to ICD-10 codes in four hospital databases.ResultsFrom 1973 to 2016 a total of 15,193 TBE cases were reported to the CDPC, 2,819 of which were reported from January 2007 through December 2016, additionally for this time period, 104 cases were identified via hospital survey. From all 2,923 reported cases (2007–2016), 1,973 met TBE case definition criteria and were included in the TBE study analysis. The highest average 10 year incidence was observed from 1990–1999 (27.9 cases per 100,000; range 4.6–53.0), however, the average 10-year incidence from 2007–2016 using officially adopted TBE case definition was 9.6 cases per 100,000 (range 5.8–14.6). For this 10-year time period most cases were adults (95.1%) and male (52.2%). The most common clinical form of TBE was meningitis (90.6%). A tick bite prior to TBE onset was reported in 60.6% of TBE cases and 98.2% of cases were not vaccinated against TBE.ConclusionThe data demonstrate that the incidence of TBE varies by about one third based on the case definition used. TBE occurs almost entirely in the unvaccinated population. Regular TBE awareness campaigns could encourage the population in Latvia to use protective measures to further control TBE in the country, either via vaccination or tick avoidance.

Highlights

Tick-Borne Encephalitis (TBE) is a potentially life-threatening infectious disease that occurs in endemic areas across the forested belt throughout Western, Central and Northern Europe through Asia to Hokkaido island in Northern Japan.[1, 2] tick-borne encephalitis (TBE) is caused by the TBE virus (TBEV), a flavivirus which is usually transmitted by infected ticks or in rare circumstances by consumption of unpasteurized dairy products from infected goats, sheep or cows
From 1973 to 2016 a total of 15,193 TBE cases were reported to the CDPC, 2,819 of which were reported from January 2007 through December 2016, for this time period, 104 cases were identified via hospital survey
A tick bite prior to TBE onset was reported in 60.6% of TBE cases and 98.2% of cases were not vaccinated against TBE

Summary

Introduction

Tick-Borne Encephalitis (TBE) is a potentially life-threatening infectious disease that occurs in endemic areas across the forested belt throughout Western, Central and Northern Europe through Asia to Hokkaido island in Northern Japan.[1, 2] TBE is caused by the TBE virus (TBEV), a flavivirus which is usually transmitted by infected ticks or in rare circumstances by consumption of unpasteurized dairy products from infected goats, sheep or cows. According to published data the number of reported TBE cases in Europe has increased by up to 193.2% in the last 30 years.[7] The availability of improved and cheaper diagnostic tests, increased disease awareness, increased outdoor activities and global warming all have been hypothesized to be contributing to the observed increasing incidence and expanding geographic distribution of the TBEV, which has become a growing public health concern in many countries.[2, 8] In addition, reliable estimates of TBE incidence are not available in most countries, before 2012 This is largely due to differences in diagnostic criteria, case definitions and valid and consistent reporting systems for TBE infection; all are problems which still exist today. To better understand the annual incidence of all TBE cases in Latvia we investigated the disease burden in the country from 1973–2016 using several available sources and case definitions

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Conclusion