Tick – borne encephalitis. Epidemiological situation in Baltic countries in 2003 – 2018

Abstract

Tick-borne encephalitis (TBE) is a typical zoonosis disease mainly transmitted to humans by hard ticks from Ixodidae family, mainly Ixodes ricinus and Ixodes persulcatus. This viral infection affects the central nervous system and can occur in people of all ages. During last decades Baltic countries remain on the European list of countries with the highest number of reported TBE cases. The aim of this study was to analyze the annual incidence of TBE cases in Lithuania, Latvia and Estonia and to explain the reasons of high incidence in these countries. We investigated the reported cases of disease during 2003-2018 using several available sources and case definitions. We also analyzed climatic parameters and impact of climate to TBE epidemiology. Among the Baltic countries, Lithuania ranks first in the number of registered cases of disease. According to Communicable diseases and AIDS Center data, from 2003 till 2018 total 7104 TBE cases were registered with range 220-763 and peaks in 2003 (n=763) and 2016 (n=632) hospitalized cases (22,9 and 21,91 cases per 100000 population, respectively). In Latvia, total 3969 TBE cases were registered with range of 142 – 494 and pick in 2010 (n=494 ) (21,97 cases per 100000 population). Estonia ranks third: total 2358 cases with range of 81-250 and peaks in 2003 (n=237) and in 2011 (n=250) (17.5 and 18.7 cases per 100000 population, respectively). Research shows that warming undoubtedly has an effect on increasing incidence of TBE. According to Lithuanian Hydrometeorological Service, in 21th century, the average annual temperature in Lithuania rose by 0.7-0.9 °C as compared with the 20th century. An increase in air temperature leads to the spread of certain types of parasites, including ticks. But we cannot assert that this is the main cause of such a high incidence in Baltic countries.