Please use Adobe Acrobat Reader to read this book chapter for free. Just open this same document with Adobe Reader. If you do not have it, you can download it here. You can freely access the chapter at the Web Viewer here. 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. 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 northwest region of Ukraine taking Volyn oblast as a sample territory during the period of 1990-2011. 3. Tikc-borne viral encephalitis 3.1. TBVE Epidemiology Virological surveillance, that has been conducted by scientists of the laboratory of Transmissible Viral Infections (TVI) of State Institution "Lviv Research Institute of Epidemiology and Hygiene Ministry of Health of Ukraine" (LRIEH), enabled detection of 38 strains of TBVE virus. Most of them (26 strains) were isolated from I. ricinus ticks, whose rate...