**2. Abiotic and biotic peculiarities of Volyn oblast**

Volyn oblast is located on far north-west part of Ukraine and occupies the western part of plain territories of two geographic zones of Ukraine – Ukrainian Polissya and Forest-Steppe. On the

© 2013 Lozynski et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

south it borders with Lviv oblast, on the east with Rivne oblast, on the north with the Republic of Belarus, on the west (along the Western Bug) with Poland.

Due to their antigen characteristics, strains of TBE virus isolated in Ukraine belong to ricinusserotype (genotype 2) and have almost same biological characteristics as causative agent of

Active Natural Foci of Tick-Borne Neuroinfections in the North-West Region of Ukraine

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For 2011 enzootic as to TBVE territories, distinguished according to one or combination of such characteristics as natural infection (presence of antigen) of ixodid ticks and small mammals (potential carriers and reservoirs of pathogen) with causative agent, diagnosed cases of the disease with local infection, high degrees of population immunity, were registered in 33

The main reservoirs of TBVE virus in nature are *Microtus arvalis*, *Myodes glareolus*, and

Among ixodid ticks, the species which are more often infected with TBE virus are *Dermacentor*

Tick-borne viral encephalitis is one of the most prevalent arboviral infections in Ukraine. People get infected with it through the tick bite or by consuming raw, mainly goat milk.

For present moment local cases of TBVE among people are registered yearly in 16 out of 25 oblasts of Ukraine, in cities Kyiv and Sevastopol. However the official data don't reflect the

During the period of 1955 to 2010 there were only 580 TBVE cases registered, while 132 of them were registered in the period of 2000–2011 (fig. 2). And correspondingly, the indices of

Central-European encephalitis of countries of Eastern and Western Europe [3, 4].

settlements of 9 districts of Volyn oblast [5] (fig.1).

**Figure 1.** Shematic map of TBVE enzootic territories in Volyn oblast

real state of things with the morbidity in Ukraine [7].

**3.2. TBVE incidence rates**

*Apodemus agrarius,* where the part of *M. arvalis* makes more than 50 %.

*reticulatus* (64,3 %), while among the *Ixodes ricinus* this number is 35,7% [6].

Climate of Volyn oblast is mild-continental, with mild winters, short periods of freezing, frequent thaws, mild summers, without significant heat waves, heavy percipitation, long springs and autumns. Average January temperature is +4,5 ⁰C, for July it is +18,6 ⁰C. Vegetation period lasts for about 200 days. The sums of the temperatures for the periods with stabile temperatures above +10, make 2495-2580 ⁰C. Percipitation makes 550-600 mm a year. Relative humidity of the air is in the reverse proportion to its temperature: in the winter it exceeds 80 %, in the summer it reaches 65-70 % [1].

Territory of Volyn oblast is the part of Eastern-European province of broadleaf forests of the European Broadleaf Zone. The landscapes of the zone are of two types: Polissya, with high prevalence of swamps, meadows, oak-pine and narrow-leaf forests and Forest-Steppe type zone, with prevalence of meadow steppes and oak-hornbeam forests in prehistoric times, which are mainly farming lands nowadays.

Due to its zoo-geographic parameters, Volyn oblast is a borreal-forest zoo-geographic type of zone. Its territory hosts 301 vertebral species, among them 183 species of nesting and nonmigrating birds, 64 species of mammals. Among small mammals, which are within the range of parasitory system of tick-borne infections, there are *Sorex araneus*, *Castor fiber*, *Аpodemus agrarius*, *Arvicolla terrestris* (*amphibious*), *Microtus oeconomus*. To woods species belong *Sciurus vulgaris*, *Microtus subterraneus*, *Meles meles*. In zoocenozes also are distributed *Dryomys nitedula*, *Glis glis*, *Muscardinus avellanarius*, *Myodes Clethrionomys glareolus*, *Sylvaemus sylvaticus, Sylvaemus tauricus, Talpa europaea, Erinaceus europaeus* [2]. All territory of the oblast is within the area of *I. ricinus* ticks - main vector of tick-borne pathogenes in Europe.

The findings of the complex studies and surveillance, conducted in the period of 1990-2011, showed the presence of active natural foci of TBVE and ITBB on the considerable part of the territory of the oblast.

**Aims of study:** to look at the incidence rates of tick-borne infectious diseases and analyse the range of their clinical manifestations in north-west region of Ukraine taking Volyn oblast as a sample territory during the period of 1990-2011.
