**4.1. Natural foci of ITBB**

In the course of our investigation of *I. ricinus* and *D. reticulatus* ticks collected in Kivertsi, Ratne and Turiysk districts of Polissya in 1998-2011, natural infectioning with *Borrelia burgdorferi s. l.* was identified in 19,8 % of *I. ricinus* and 3,8 % of *D. reticulatus* on the average. The highest prevalence of infected *I. ricinus* – 25,0 % - was identified in Kivertsi, Ratne (19,3 %) and Manevychi (16,7 %) districts, while the lowest rates were reported from Turiysk - 6,7 %. Sixtytwo population units in all 16 districts of the oblast were found ITBB enzootic.

The same districts had on the average 1,6 times higher level of the specific antibodies among the group of high professional risk (forestry workers), which was anticipated. This can be expained by the permanent being in natural foci, they contact with infected ticks more often (table 2). The antibodies were detected in 129 out of 281 (45,9 %) of the screened persons.

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

 Kivertsi 46 29 63,0 Kovel skyi 74 25 33,8 Manevychi 21 9 42,8 Ratne 39 24 61,5 Rozhyshche 65 26 40,0 Staro-Vyzhva 36 16 44,4 Total 281 129 45,9

Upon observation of 1117 patients from 15 administrative districts of Volyn oblast, who were suspected of having ITBB or diagnosis which don' t exclude it (primarily with the preliminary diagnosis of TBVE), the antibodies to *B. burgdorferi s. l.* in diagnostic titres (1:100-1:1600) were

> **Number of patients\***

 Volodymyr-Volynskyi 34 5 14,7 3,9 Gorokhiv 20 3 15,0 1,9 Ivanychi 76 11 14,5 3,7 Kamin-Kashyrsk 18 2 11,1 2,7 Kivertsi 150 21 19,0 3,6 Kovel 127 28 22,0 3,5 Lokachi 19 3 21,4 4,4 Lutsk yi (incl. Lutsk city) 262 92 35,1 5,3 Liubeshiv 18 3 16,7 8,3 Liuboml 14 3 21,4 7,5 Manevychi 31 5 16,1 2,3 Ratne 225 72 32,0 12,6 Rozhysche 62 7 11,3 4,3 Staro-Vyzhva 14 2 14,3 3,2 Shatsk 47 7 14,9 5,9 Total 1117 267 23,9 2,1

**Antibodies found:**

**Range of morbidity\*\* <sup>n</sup> %**

**Found positive: n %**

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151

**№ Districts Total of observed patients**

**Table 2.** Seroprevalence of ITBB in human risk groups from different areas of Volyn oblast

**4.3. Epidemiology**

detected in 267 (23,9 %) (table 3).

\* - number of patients observed with the fever and a tick bite

\*\* - range of morbidity (mean for 2000-2011 year, per 100 000 population)

**Table 3.** Results of serologic revealtion of ITBB patients in Volyn oblast

**№ Districts**

#### **4.2. Population immunity**

The evidence of the endemic status of ITBB natural foci on the territory of the oblast were collected in terms of serologic screening of 2122 persons among healthy population of five districts of Ukrainian Polissya (Kivertsi, Kovel, Manevychi, Ratne and Rozhysche) and three districts of a Forest-Steppe zone (Volodymyr-Volynskyi, Ivanychi and Lutsk) (table 1).

Seropositive layer of screened persons was within the range of 18,6-45,6 % (the mean value for oblast was 28,6 %), thus exceeding 10 % threshold - the estimated level of active natural foci of Lyme-borreliosis in other districts [14]. More than 20 % of population in 5 out of 12 screened districts of Volyn oblast (Volodymyr-Volynskyi, Gorohiv, Kovel, Lutsk and Ratne were found to have higher titres of Ig G antibodies (1:400-1:1600).


**Table 1.** Seroprevalence of ITBB in human probands from different areas of Volyn oblast

The same districts had on the average 1,6 times higher level of the specific antibodies among the group of high professional risk (forestry workers), which was anticipated. This can be expained by the permanent being in natural foci, they contact with infected ticks more often (table 2). The antibodies were detected in 129 out of 281 (45,9 %) of the screened persons.


**Table 2.** Seroprevalence of ITBB in human risk groups from different areas of Volyn oblast

#### **4.3. Epidemiology**

**4. Ixodid tick-borne borreliosis (Lyme Borreliosis)**

to have higher titres of Ig G antibodies (1:400-1:1600).

In the course of our investigation of *I. ricinus* and *D. reticulatus* ticks collected in Kivertsi, Ratne and Turiysk districts of Polissya in 1998-2011, natural infectioning with *Borrelia burgdorferi s. l.* was identified in 19,8 % of *I. ricinus* and 3,8 % of *D. reticulatus* on the average. The highest prevalence of infected *I. ricinus* – 25,0 % - was identified in Kivertsi, Ratne (19,3 %) and Manevychi (16,7 %) districts, while the lowest rates were reported from Turiysk - 6,7 %. Sixty-

The evidence of the endemic status of ITBB natural foci on the territory of the oblast were collected in terms of serologic screening of 2122 persons among healthy population of five districts of Ukrainian Polissya (Kivertsi, Kovel, Manevychi, Ratne and Rozhysche) and three districts of a Forest-Steppe zone (Volodymyr-Volynskyi, Ivanychi and Lutsk) (table 1).

Seropositive layer of screened persons was within the range of 18,6-45,6 % (the mean value for oblast was 28,6 %), thus exceeding 10 % threshold - the estimated level of active natural foci of Lyme-borreliosis in other districts [14]. More than 20 % of population in 5 out of 12 screened districts of Volyn oblast (Volodymyr-Volynskyi, Gorohiv, Kovel, Lutsk and Ratne were found

> **Total of observed patients**

 Volodymyr-Volynskyi 114 52 45,6 49 43,0 Gorokhiv 99 30 30,3 30 30,3 Ivanychi 20 5 25,0 0 0 Kamin-Kashyrs 59 11 18,6 10 16,9 Kivertsi 452 124 27,4 80 16,9 Kovel 206 80 38,8 37 18,0 Liubeshiv 111 31 27,9 31 27,9 Lutsk 194 64 33,0 57 29,4 Manevychi 347 80 23,0 64 18,4 Ratne 418 108 25,8 96 23,0 Rozhysche 49 12 24,5 11 22,4 Staro-Vyzhva 53 14 26,4 6 11,3 Total 2122 609 28,6 471 22,2

**Table 1.** Seroprevalence of ITBB in human probands from different areas of Volyn oblast

**Found positive:**

**incl. in titres 1:400-1:1600 n %**

**n %**

two population units in all 16 districts of the oblast were found ITBB enzootic.

**4.1. Natural foci of ITBB**

150 Encephalitis

**4.2. Population immunity**

**№ Districts**

Upon observation of 1117 patients from 15 administrative districts of Volyn oblast, who were suspected of having ITBB or diagnosis which don' t exclude it (primarily with the preliminary diagnosis of TBVE), the antibodies to *B. burgdorferi s. l.* in diagnostic titres (1:100-1:1600) were detected in 267 (23,9 %) (table 3).


\* - number of patients observed with the fever and a tick bite

\*\* - range of morbidity (mean for 2000-2011 year, per 100 000 population)

**Table 3.** Results of serologic revealtion of ITBB patients in Volyn oblast

According to the data of clinically-epidemiological survey of 267 laboratory-confirmed cases, we determined the main clinical manifestations and epidemiologic peculiarities of ITBB.

All age groups were found vulnerable to ITBB - from the age of 1,2 to 80 years old people. Children below 10 and senior citizens (above 60) get sick less often - 9,0 % and 9,8 % (5 persons) respectively (fig. 5). Age risk group is the one of adult working age, 31-60 years old (52,7 % of

9,8 %

Concerning the socially-professional structure of the disease, the highest risk of infectioning (62,2 %) was detected among office and labour workers, pensioners and unemployed.

The spectrum of the main clinical manifestations was analysed according to the reported cases

ME 156 58,4 64,9 Syndrome of total infectioning 182 68,2 43,3 Nervous system lesions 86 37,0 21,4 Locomotor system lesions 56 21,0 24,1 Heart lesions 23 8,6 8,3

19,5 %

**Figure 5.** ITBB cases by age in Volyn oblast, 2000-2011 (n= 267)

9,0 %

12,0 %

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

most of 61 years from 51 ap 60 years from 41 ap 50 years from 31 ap 40 years from 21 ap 30 years from 11 ap 20 years from 1 ap 10 years

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153

**Detection rates: Volyn oblast Ukraine n % %**

21,2 %

cases, 141 persons).

15, 0 %

**4.4. Clinical manifestations**

and was found typical for ITBB (table 4).

**Clinical manifestations**

**Table 4.** Frequency and spectrum of ITBB clinical manifestations

13,5 %

Almost 80 % (77,9 %) of the patients experienced the tick bite or "unknown insect's bite", which preceded the development of the disease. The incubative period in the course of tick borrelioses lasted 10 days on the average-from 3 to 45 days.

Seasonal character of tick borrelioses - spring-summer, which responds to the period of seasonal activity of *I. ricinus* ticks. First cases are reported in April, peak of prevalence (45,0 %) is observed in June, July and August, the latest new cases come out in November. Thus the season of the highest risk of infectioning lasts for 6-8 months - from April to November. If we compare encephalitis and tick-brome borreliosis, we can see that the cases of ITBB (up to 14-15 %), are reported in winter and early spring, but this is related to the clinical manifestations of 2-3 stages of the disease (fig. 4).

**Figure 4.** Seasonal distribution of ITBB cases in Volyn oblast, 2000-2011 (n= 267)

Within the structure of patients with the laboratory confirmed diagnosis of ITBB there prevailed the residents of big and small towns of the region - 58,1 % (154), rural population's part made 41,9 % (111). The zones of major infectioning were forest zones and forest-park zones attached to them. Seventy cases of infectioning occurred within the rural/countryside areas (26,2 %). There was a new phenomena in the science of epidemiology observed - a considerable urbanization of natural foci: 13,1 % of patients were infected on the territory of recreation zones (parks, natural relax zones, gardens, etc) of oblast's center - Lutsk city as well as districts' centers. In fact, we have ample evidence to claim that there are not natural foci, but anthro‐ purgic and transient foci of ITBB and other TBI on the territory of Volyn oblast.

Within the gender structure of patients male made 40,2 %, female - 59,8 %.

All age groups were found vulnerable to ITBB - from the age of 1,2 to 80 years old people. Children below 10 and senior citizens (above 60) get sick less often - 9,0 % and 9,8 % (5 persons) respectively (fig. 5). Age risk group is the one of adult working age, 31-60 years old (52,7 % of cases, 141 persons).

**Figure 5.** ITBB cases by age in Volyn oblast, 2000-2011 (n= 267)

Concerning the socially-professional structure of the disease, the highest risk of infectioning (62,2 %) was detected among office and labour workers, pensioners and unemployed.

#### **4.4. Clinical manifestations**

According to the data of clinically-epidemiological survey of 267 laboratory-confirmed cases, we determined the main clinical manifestations and epidemiologic peculiarities of ITBB.

Almost 80 % (77,9 %) of the patients experienced the tick bite or "unknown insect's bite", which preceded the development of the disease. The incubative period in the course of tick borrelioses

Seasonal character of tick borrelioses - spring-summer, which responds to the period of seasonal activity of *I. ricinus* ticks. First cases are reported in April, peak of prevalence (45,0 %) is observed in June, July and August, the latest new cases come out in November. Thus the season of the highest risk of infectioning lasts for 6-8 months - from April to November. If we compare encephalitis and tick-brome borreliosis, we can see that the cases of ITBB (up to 14-15 %), are reported in winter and early spring, but this is related to the clinical manifestations of

lasted 10 days on the average-from 3 to 45 days.

2-3 stages of the disease (fig. 4).

2,2

February

0

January

5

10

15

20

25

**%**

152 Encephalitis

4,5

1,1

March

3

**Figure 4.** Seasonal distribution of ITBB cases in Volyn oblast, 2000-2011 (n= 267)

April

8,9

May

10,6

June

purgic and transient foci of ITBB and other TBI on the territory of Volyn oblast.

Within the gender structure of patients male made 40,2 %, female - 59,8 %.

July

Within the structure of patients with the laboratory confirmed diagnosis of ITBB there prevailed the residents of big and small towns of the region - 58,1 % (154), rural population's part made 41,9 % (111). The zones of major infectioning were forest zones and forest-park zones attached to them. Seventy cases of infectioning occurred within the rural/countryside areas (26,2 %). There was a new phenomena in the science of epidemiology observed - a considerable urbanization of natural foci: 13,1 % of patients were infected on the territory of recreation zones (parks, natural relax zones, gardens, etc) of oblast's center - Lutsk city as well as districts' centers. In fact, we have ample evidence to claim that there are not natural foci, but anthro‐

August

September

21,3

13,1

7,9

October

November

9,7

4,5

December

6,5 6,7

No dates

The spectrum of the main clinical manifestations was analysed according to the reported cases and was found typical for ITBB (table 4).


**Table 4.** Frequency and spectrum of ITBB clinical manifestations

The initial clinical manifestation of the disease was erythema migrans (58,4 %) and a syndrome of total infectioning (68,2 %).

for Ukraine - 80,9 %, and also the manifestations of total infectioning syndrome - hyperthermia,

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Overall, the analysis of the clinical course of non-erythemic forms of ITBB and comparing it to erythemic forms, shows that the course of the former was more complicated with the involvement of infectioning of other organs and systems, than that of the latter (fig. 6.)

**Figure 6.** Spectrum of neurological manifestation in patient of erythemic and non-erythemic forms.

vegetative-1,3 times more often.

There were observed certain differences such as the syndrome of total infectioning with higher and continuous fever, which needs to be confirmed by a larger studies. The symp‐ toms as the headache and dizcyness were observed 1,5 times more often, syndrome astheno‐

As for the gender structure, male prevailed and made 53,5 %, while the part of female was 46,5 %. The age of patients was fluctuating of 1,2 up to 80 years, but neurology pathology was observed in children under 10 (18,6 %), teenagers (16,3 %) more often, while the largest group (40,7 %) was made of the persons of working age: 31-40 (25,6 %) and 41-50 (15,1 %) years old.

Up to 50 % of the patients with the borreliosis lesions of the nervous system were sick in the period June-October after the incubatory period, that lasted from few days to few weeks.

Taking into consideration the neuroborreliosis manifestations (neurologic lesions) observed in one third of the patients, we conducted a target serologic examination for ITBB of the patients of out-hospital departments of Volyn oblast. In the course of the examination of 107 patients with the neurologic lesions (hemyparesis, paresthesia, myalgia), the antibodies to Borrelias

were detected in 20 (28,9 %), among them 10 cases (27,9 %) - had it in higher titres.

fatigness, dizzyness in 21,4% (for Ukraine on the whole - 24,1 %).

A heart pathology was observed in 8,6 % of patients. Ischemic disease, myocarditis and pericarditis etc were diagnosed in regard to the cardio-vascular lesions.

On the other hand, in more than 20 % of the patients the course of the disease was characterised by the manifestations of locomotor system, the lesions of joints (arthritis, arthralgia) and periarticular tissues (bursitis, synovitis, plexitis).

Neurologic lesions, which are considered to be as prevalent lesions in the course of ITBB as erythema migrans in Europe [4], were observed in 37,0 % of patients, which is 16 % more than in Ukraine on the whole. Thus, according to the accumulative data, in regard to the clinical manifestations in the country on the whole, locomotor system lesions take the second place, after erythema migrans, and make 24,1 %. While in Volyn oblast the second most prevalent manifestation is neuroborreliosis. Taking into consideration the known fact, that there is an ethiologic mutual dependence between some genotypes of a causative agent and nozologic types of ITBB [15, 16], it can be assumed that the considerable prevalence of the patients with nervous system lesions can be caused by the prevalence of *B. garinii* within the spectrum of *B. burgdorferi s. l*., which is believed to be the cause of neuroborreliosis.

On the acute stage of the disease, among the main manifestations of neuroborreliosis there were lesions of both peripheric nervous system (migrating pains, mono- and polyneuritis of scull nerves, polyradiculoneuritis, lack of skin sensitivity of a local character, paresthesia, relapsing neuritis of a facial nerve), which appeared mostly on the acute stage of the disease, and of central nervous system - manifested by meningitis, encephalitis, meningoencyphalitis, arachnoiditis, rigidity of neck muscles, nausea, headache, which manifested on the second stage of ITBB development. It has to be noted that in Ukraine, the major part of complicated lesions of the central nervous system in the course of ITBB is mainly observed in three oblasts – Volyn, Kherson and Zaporizzya.

On the second stage of Lyme Borreliosis the lesions of a cerebral cortex were manifested by different encephalopathia (9,5 %), such as speech problems, coordination, sleep, sight, memory, short-term black-outs. In a part of the patients (3,43 %) we were observing the signs of astheno-neurotic syndrome, such as often headaches, fatiguability, migrains, nervousness etc, some patients (1,47 %) had torpid paresis of facial muscles, in some rare case (0,49 %) the epileptic syndrome developed.

Cerebrospinal fluid has lymphocitaric pleocitosis, number of cells - dozens and hundreds in 1 mkl; lymphocitis make 70-100 % of total amount of cells, quite often, especially in the course of meningoradiculitis, there is an increase in protein amount - sometimes more than 1-2 mmol/l.

#### **4.5. Neurologic manifestations with or without a erythema migrans**

The peculiar feature of neuroborreliosis in Volyn oblast is the lack of the migratory erythema at the initial stage of the disease in 81,4 % of patients, which approximately equals the number for Ukraine - 80,9 %, and also the manifestations of total infectioning syndrome - hyperthermia, fatigness, dizzyness in 21,4% (for Ukraine on the whole - 24,1 %).

The initial clinical manifestation of the disease was erythema migrans (58,4 %) and a syndrome

A heart pathology was observed in 8,6 % of patients. Ischemic disease, myocarditis and

On the other hand, in more than 20 % of the patients the course of the disease was characterised by the manifestations of locomotor system, the lesions of joints (arthritis, arthralgia) and

Neurologic lesions, which are considered to be as prevalent lesions in the course of ITBB as erythema migrans in Europe [4], were observed in 37,0 % of patients, which is 16 % more than in Ukraine on the whole. Thus, according to the accumulative data, in regard to the clinical manifestations in the country on the whole, locomotor system lesions take the second place, after erythema migrans, and make 24,1 %. While in Volyn oblast the second most prevalent manifestation is neuroborreliosis. Taking into consideration the known fact, that there is an ethiologic mutual dependence between some genotypes of a causative agent and nozologic types of ITBB [15, 16], it can be assumed that the considerable prevalence of the patients with nervous system lesions can be caused by the prevalence of *B. garinii* within the spectrum of *B.*

On the acute stage of the disease, among the main manifestations of neuroborreliosis there were lesions of both peripheric nervous system (migrating pains, mono- and polyneuritis of scull nerves, polyradiculoneuritis, lack of skin sensitivity of a local character, paresthesia, relapsing neuritis of a facial nerve), which appeared mostly on the acute stage of the disease, and of central nervous system - manifested by meningitis, encephalitis, meningoencyphalitis, arachnoiditis, rigidity of neck muscles, nausea, headache, which manifested on the second stage of ITBB development. It has to be noted that in Ukraine, the major part of complicated lesions of the central nervous system in the course of ITBB is mainly observed in three oblasts

On the second stage of Lyme Borreliosis the lesions of a cerebral cortex were manifested by different encephalopathia (9,5 %), such as speech problems, coordination, sleep, sight, memory, short-term black-outs. In a part of the patients (3,43 %) we were observing the signs of astheno-neurotic syndrome, such as often headaches, fatiguability, migrains, nervousness etc, some patients (1,47 %) had torpid paresis of facial muscles, in some rare case (0,49 %) the

Cerebrospinal fluid has lymphocitaric pleocitosis, number of cells - dozens and hundreds in 1 mkl; lymphocitis make 70-100 % of total amount of cells, quite often, especially in the course of meningoradiculitis, there is an increase in protein amount - sometimes more than 1-2 mmol/l.

The peculiar feature of neuroborreliosis in Volyn oblast is the lack of the migratory erythema at the initial stage of the disease in 81,4 % of patients, which approximately equals the number

pericarditis etc were diagnosed in regard to the cardio-vascular lesions.

*burgdorferi s. l*., which is believed to be the cause of neuroborreliosis.

**4.5. Neurologic manifestations with or without a erythema migrans**

periarticular tissues (bursitis, synovitis, plexitis).

of total infectioning (68,2 %).

154 Encephalitis

– Volyn, Kherson and Zaporizzya.

epileptic syndrome developed.

Overall, the analysis of the clinical course of non-erythemic forms of ITBB and comparing it to erythemic forms, shows that the course of the former was more complicated with the involvement of infectioning of other organs and systems, than that of the latter (fig. 6.)

**Figure 6.** Spectrum of neurological manifestation in patient of erythemic and non-erythemic forms.

There were observed certain differences such as the syndrome of total infectioning with higher and continuous fever, which needs to be confirmed by a larger studies. The symp‐ toms as the headache and dizcyness were observed 1,5 times more often, syndrome astheno‐ vegetative-1,3 times more often.

As for the gender structure, male prevailed and made 53,5 %, while the part of female was 46,5 %. The age of patients was fluctuating of 1,2 up to 80 years, but neurology pathology was observed in children under 10 (18,6 %), teenagers (16,3 %) more often, while the largest group (40,7 %) was made of the persons of working age: 31-40 (25,6 %) and 41-50 (15,1 %) years old.

Up to 50 % of the patients with the borreliosis lesions of the nervous system were sick in the period June-October after the incubatory period, that lasted from few days to few weeks.

Taking into consideration the neuroborreliosis manifestations (neurologic lesions) observed in one third of the patients, we conducted a target serologic examination for ITBB of the patients of out-hospital departments of Volyn oblast. In the course of the examination of 107 patients with the neurologic lesions (hemyparesis, paresthesia, myalgia), the antibodies to Borrelias were detected in 20 (28,9 %), among them 10 cases (27,9 %) - had it in higher titres.

In some patients (6,86 %), the course of the disease and the character of neurologic mani‐ festations (acute outset, temperature reaction, rigidity of neck muscles, fading of reflexes, inflammation of CLS, etc), Lyme Borreliosis was very similar to TBVE, especially in its encephalopoliomyelitic manifestations, which lead to the preliminary diagnosis of TBVE, which was not confirmed by the further serologic tests. Similar indicators of the disease are observed in some regions of Russia [17], but are manifested very rarely in patients from other countries.

In Volyn oblast, we got the evidence of the existance of territory-connected natural foci of ITBB and TBVE for 6 districts (fig. 7). The existance of population-connected foci of these two zoonoses is proven by cases of mixed-infectioning of *I. ricinus* ticks with TBE virus and *Borrelia burgdorferi s. l*., which we detected in Kovel and Kivertzi districts, and *D. reticulatus* ticks - in

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On the territory of oblast out of 267 cases of ITBB 29 (10,9 %) appeared to be TBVE mixed infection: the majority of them were found in Ratne (18) and Lutsk (8) rayons, few of them in

**1.** North-West region of Ukraine is one of the regions with high prevalence of TBVE and

**2.** There are an active natural foci of TBVE and ITBB in Ratne district of Volyn oblast. High epidemic potential is confirmed by isolation of TBE virus strains, detection of the antigen of a causative agent in vectors and reservoirs, as well as by a population morbidity.

**3.** We found the evidence to confirm the previously made hypothesis as for the existance of polivector (binar) TBVE and ITBB foci in Ukraine, where the circulation of the causative agent is done by two dominating species of *ixodids* - *Ixodes ricinus* and *D. reticulatus*, which makes the risk of a population infectioning higher. The range of vertebral-reservoirs of causative agents of Lyme Borreliosis and TBVE, includes not only those known in Europe,

**4.** The TBVE incidence manifests itself by regular sporadic cases of the disease and out‐ breaks. In terms of clinical manifestations, there dominate forms with total-infectioning with the non-malignant course of the disease (60 %). Meningeal forms make 24 %,

**5.** ITBB is an endemic disease for Volyn oblast, caused by the presence of *I. ricinus* and *D. reticulatus* ticks there. High prevalence rates are reported in Kivertsi, Lutsk, Manevychi, Ratne, Rozhysche districts, were 16,7 % up to 25 % of ticks are infected with the ITBB causative agent, the rates of population contact with ticks is within 30-40 %, risk group makes 40-60 %, mean indicator of the incidence (based on many years of surveillance) is

**6.** The range of clinical manifestations of ITBB includes most of symptoms, which are described in scientific literature: starting from the erythema migrans, and syndrome of total infectioning to nervous system lesions, as well as lesions of locomotor and cardiovascular system. The distinctive feature of the manifestations of the acute form of the disease is high prevalence of non-erythemic forms (41,6 %) as well as high percentage of

Kivertzi (2), Kovel (1), Lyubeshiv (1) and Shatsk (1) districts [19].

but also other species of small mammals.

meningo-encephalitic -16 %.

0,39-4,33 per 100 000 population.

cases with nervous system involvement (37,0 %).

Manevychi, Ratne and Kovel districts.

**5. Conclusions**

ITBB.

#### **4.6. Mixed infections of TBVE-ITBB**

The presence of causative agents of different diseases (TBVE, ITBB, HGA) in parazyte systems, common vectors (*I. ricinus* and *D. reticulatus* ticks) and host-reservoirs (*Myodes glareolus* and *Sorex araneus* etc) with certain residing areas of each, predetermine similarities in epidemio‐ logic structure of these infections. It is proved that one ixodid tick can contain 5-7 pathogenes at the same time [18]. The main social factors, predetermining the main features of TBVE, ITTB and HGA are also similar. Given all these facts, it may cause regular simultaneous infectioning of people with several causative agents.

**Figure 7.** Connected natural foci of ITBB and TBVE in Volyn oblast

Retrospective analysis showed that the considerable part of cases with the preliminary diag‐ nosis of TBVE, was, in fact, the cases of neuroborreliosis, including mixed infections of TBVE and neuroborreliosis.

In Volyn oblast, we got the evidence of the existance of territory-connected natural foci of ITBB and TBVE for 6 districts (fig. 7). The existance of population-connected foci of these two zoonoses is proven by cases of mixed-infectioning of *I. ricinus* ticks with TBE virus and *Borrelia burgdorferi s. l*., which we detected in Kovel and Kivertzi districts, and *D. reticulatus* ticks - in Manevychi, Ratne and Kovel districts.

On the territory of oblast out of 267 cases of ITBB 29 (10,9 %) appeared to be TBVE mixed infection: the majority of them were found in Ratne (18) and Lutsk (8) rayons, few of them in Kivertzi (2), Kovel (1), Lyubeshiv (1) and Shatsk (1) districts [19].
