The occurrence of the Dermacentor reticulatus tick – expansion to new areas
and their possible reasons
Grzegorz Karbowiak
W.Stefanski Institute of Parasitology, Polish Academy of Sciences
Twarda 51/55, 00-818 Warsaw, Poland
Abstract
Dermacentor reticulatus tick can be found in temperate zones of Eurasia. Their area of
occurrence is divided into two parts: west and east. Presently, D. reticulatus spread their area
through the older free zone. The possible reasons for dividing the previous area into two parts
is the climatic structure of Europe, for example the specific mean winter and summer
temperatures. The region where D. reticulatus is absent is characterised by mean winter
temperatures between 0C and 5C and thin snow cover. The alternative hypothesis is the
effect of human influence - liquidation of habitats of this tick and eradication of their hosts.
The present expansion can be the effect of climate changes. The mean temperatures in Europe
increased, following the elongation of the vegetation season and positive trends of wet days
are observed. Consequently, northern Europe has become warmer and wetter over the last
century.
Human activity can also influence the spreading of the ornate dog tick. The possible factors
are the changes in agricultural land-use, environmental protection and spreading with
international tourism and trade. In summary, the expansion of Dermacentor reticulatus tick
into new areas could be the synergistic effect of many favourable factors.
Key words: Dermacentor reticulatus;
Introduction
In middle Europe, Dermacentor reticulatus is the second most important hard tick
species after the common tick Ixodes ricinus, in respect to their number and impact on the
economy. The most important hosts for adult ticks are wild and domestic ruminants, horses
and dogs, whereas for larvae and nymphs, this is rodents and insectivores. Humans are very
seldom attacked by this tick. First-hand consequences of feeding are damage to skin and
stress; in addition, the D. reticulatus tick is the main vector of Babesia canis and other
piroplasms species, and is also able to transmit tularaemia, rickettsioses and other pathogens.
Due to, this tick has the great epidemiological importance in Europe.
1. The preferred habitats of D. reticulatus tick
D. reticulatus occurs in mild, damp open areas that are weakly covered by trees and
bushes. It favours natural deciduous forests placed near water bodies or large stagnant waters.
Therefore, it is most common in the wet forest associated with river valleys and ravine
systems, lake shores and meadows near the forests borders. Typical biotopes are swampy
mixed woods, meadows and shrub pasture communities. The most important factor for their
occurrence is the high level of ground water, along with the drying up of soil [1, 2, 3]. In the
area of the former Soviet Union, it also occurs in typical marshes [4, 5].
Data about the vertical distribution of this tick are pure. It seems to be strongly
associated with lowland regions. Široký et al. [6] reported the biggest population of ticks in
localities situated at altitudes at 177 m above sea level and only single locations above 200 m
a.s.l.
The characteristic feature of D. reticulatus is the ability of adaptation to different
habitats, whilst under continuous human influence and fairly anthropogenic environments [7,
8, 9]. Széll et al. [10] consider this tick to be anthropophilic. As a result, their occurrence is
not limited to natural plant communities, but with Ixodes ricinus and Haemaphysalis
concinna, it is spread in urban areas. In towns and urban agglomerations, it inhabits
recreational areas, featuring afforestation and/or conglomerates of bushy vegetation. In the
parks, these are areas that have been created from natural meadows and forests, with parts of
primeval herbage. Due to the small number of regular observations, it is difficult to determine
a general principle of the occurrence and activity of ticks under urban conditions. The
gathering of ticks is mainly conducted for epidemiological purposes, and authors seldom note
the ecological data, such as the type of plant communities, the time of the study and the
meteorological conditions. Little indirect information is available in veterinary clinics where
dogs infected with babesiosis have been cured.
2. The occurrence area of D. reticulatus in the last decade of 20th Century
The D. reticulatus tick is found in the western Palaearctic region, in a temperate forest
climate zone of Eurasia, from England and France in the west to the basin of Yenisei River in
Siberia in the East. The northern border of their range runs along the 56-57° N geographical
latitude, while the commonly sustained southern border is 50° N geographical latitude [3, 11];
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however, there are documented populations from Portugal, located in 39 and 50° N [12] and
in Romania and Hungary between 50 and 46° N [13, 14, 15]. According to Immler [2], the D.
reticulatus tick occurrence area is limited to regions with 400 to 1000 mm of spring
precipitation and a summer isotherm of 20-22C. However, a wider occurrence area in the
past is possible. Within the geographic range, D. reticulatus is distributed in a highly focal
pattern, which is associated with their habitat needs [16]. Their occurrence area is
characterised by phenomena that are not observed in other tick species and are generally rare
in nature. Namely, it is divided into two separate parts – Western Europe and Eastern Europe
[2, 11, 17]. The western region covers the populations occurring from France to eastern
Germany. In France D. reticulatus ticks were recorded in the highland of southern Jura, in the
Rhone Valley, Northern French Alps [18] and Ardenes [19, 20]. In Germany, D. reticulatus
tick populations were found in Taurus Mountains, Schwarzwald and Bayern [1], to Leipzig on
the East [21]. The single, isolated foci of D. reticulatus ticks is recorded in Holland [22],
south-western England [2] and Portugal [23].
There are some populations in Austria, the Czech Republic and western Slovakia;
however, they can be regarded as single foci. Hubalek et al. [24] described the populations
occurring in northern Austria, which are associated with the population in the Czech Republic
and western Slovakia. These ticks are present in southern Moravia and Danuba rivers-basin
and regions along the southern Slovakian border between Bratislava and Komarno [25, 26,
27].
In the area of the Eastern range of the occurrence, the D. reticulatus tick is common
from eastern parts of Poland, across Belarus and the European part of Russia to the Central
Siberian Plateau. In Russia, large populations were noted in the Smolensk and Moscow
districts [28, 29]. In the St. Petersburg district (59º N), where the northern border of the
occurrence exists, this tick is relatively rare [30].
The northern border of the occurrence area run across the districts of Moscow,
Ivanovsky, Ryazan, Svierdlovsk, Tyumentsevsky, Omsk, Novosibirsk and Kansk to the
Khemerovsky district [31, 32]. To the East, the range of this tick reaches the Krasnoyarsk
region. In the Asiatic part of Russia, a number of populations are present across Northern
Caucasus and eastern South Caucasus. The strong populations were noted in southern parts of
Omsk and Nowosibirsk districts and in Altai, where the D. reticulatus tick forms sympatric
populations with D. marginatus [33, 34]. The southern border of the East occurrence area of
D. reticulatus tick in Europe involves the Crimean Mountains, Northern Caucasus, eastern
Kazakhstan, and western Altai [1].
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It is difficult to establish the eastern border of the D. reticulatus range, because it is not
possible to determine whether the records from Siberia regard this species, or are
determinations of other, morphologically similar species from the Dermacentor genus.
In Belarus, the D. reticulatus tick is the most numerous in Polesie and its range reaches
Vilnius, where the biggest populations are recorded in the Gomel district. The smaller
populations occur in the Minsk district [35, 36, 37]. These populations are conjoined with
Polish populations in Podlasie and these ranges should in fact be considered as one.
In the Ukraine, the D. reticulatus tick is noted in the central part of the country, among
other regions of Kiev, in Dnieper River Lowland and in Samara River basin [4, 38].
The populations in the eastern part of Slovakia belong to the Eastern occurrence area of
D. reticulatus. The foci are placed along the southern and eastern country border, in the
midcourse of the Latorica River. In Romania and Hungary, this tick is quite common in
northern provinces and relatively rare in other parts of the countries [15, 39].
There is a region where the D. reticulatus tick is absent in the middle of Europe. This
area is approximately triangular in shape. The northern edge runs along the Baltic Sea coast,
with the arms extended from central Germany and western Poland, between 12-13 and 19
meridian of the eastern longitude; the arms of the triangle coincide, reaching the southern
border of Hungary [8, 40].
3. The changes in the occurrence range of D. reticulatus tick
The occurrence area of D. reticulatus tick described above was relatively stable from
the first species descriptions until the 1970s and 1980s. Since the last decade of the previous
century, it has appeared in new localities, where it was previously absent.
The first comprehensive study of the occurrence area in Poland was made by Lachmajer
in 1963 [41] and later completed by Szymański (1986) [42] and Siuda in 1993-1995 [3, 11].
The picture of the occurrence area presented by these authors was the basis for every
elaboration concerning this tick species, which appeared from the last years of the 20th
century to the beginning of the 21st century. According to their data, in Poland, this tick
occurred in the north-eastern parts of the country, in Podlasie, Augustowska Forest,
Knyszyńska Forest, in the Biebrza River Valley, Piska Forest and Lublin Polesie. This
occurrence area is presented in Fig. 1. Siuda [11] and Siuda et al. [17] collected 10
documented foci, which were the borders of the Eastern occurrence area, which included
regions on the east of the Vistula and San rivers. According to the new study and reports, it
should be considered the single, contiguous area connected with the main, so-called Russian
4
occurrence area [43], and the reports of the new foci have epidemiological importance only,
because no foci are separated in the fact.
From the 1990s, in Poland, the expansion of this tick species to the west was observed.
Among others, the appearance of new localities of this tick were recorded in northern Poland,
in Pomeranian province, Kashube and in Tuchola Woods [44, 45], in the central regions in
Kampinos Forest near Warsaw, as well as in the borders of Warsaw agglomeration [7, 9, 40].
In the south of the country, in Niepołomice, this tick was transferred from Białowieża
Primeval Forest with European bisons [46]. Recently, the newly documented foci have been
observed in the south-western part of Poland in Lower Silesia since 2009, when the first
evidence was noted in the Bolesławiec County [47, 48] and in Lubuskie Province [49].
The expansion of D. reticulatus tick to the new, previously free areas has been observed
in all of the middle and northern parts of Europe (Fig. 2). Until the late 1970s, this tick was
relatively rare in Germany [2]. In the 1980s, it remained more common in the western part of
the country and still rare in eastern lands – there were three populations in present in the
Leipzig district. In the last decade of the 20th century there were found some foci in eastern
Germany in Düben-Dahlen and Annaburg, which were considered endemic [50]. D.
reticulatus remains numerous in Saxony, Saxony-Anhalt, Brandenburg, and the previously
small populations in Hessen and Bayern have recently enlarged [51].
A similar situation concerns the Czech Republic and Slovakia. Until the 1980s, this tick
was rarely found, and the foci were documented around Bratislava, along the Danube and
Bodrog rivers, and near the Ukraine border [27]. In the last decade, many new localities have
appeared; however, as they were distinct to Poland, the main expansion direction was from
the west to the east, into the East Slovakian Upland. Simultaneously, the tick species in the
Danube valley has spread to the west, and has come into contact with the D. reticulatus ticks
from West-European and Eastern occurrence areas [52]. Apart from this, the expansion to the
north has been observed; the northern range border in Slovakia reaches Michalovce, Trebišov
and Košice towns [53]. In the Czech Republic, the distribution range of D. reticulatus has not
increased to such a degree as in Poland and Slovakia and is present along the main rivers
usually; however, there is evidence of their increased abundance [6]. In Hungary, there were
two, separate foci of this tick in the 1950s, and until the 1970s this tick was seldom found. In
recent decades, the expansion of this species was observed and it presently occurs in the
whole country; moreover, it is more numerous [54]. The most numerous populations are
recorded in north-western and south-western parts of the country [13, 14, 15, 55].
5
The occurrence of new areas in eastern Germany (from 20006), western Poland (from
2010) and the Czech Republic (from 2010) are correlated in time – the expansion of the whole
west-European population to the East is evident.
Recently, new populations of D. reticulatus ticks have been recorded in Belgium,
confirming the geographical expansion in North-western Europe [56].
4. The possible sources of the separated occurrence ranges presence.
The reasons for the presence of two separate occurrence areas of D. reticulatus tick
until the end of the 20th century end, as well as their present fusion, are not known. The
hypotheses usually concern the environmental and climatic conditions; however, the human
activity impact is also possible.
There is no geographic barrier between natural forest and meadow ecosystems in the
Palaearctic zone along the lane from France to Ural between 50 and 55 northern latitudes. For
this reason, human activities may be the factors that are accountable for the absence of this
tick in the middle of Europe. Such factors can be melioration and the eradication of
streamlets, as well as the decrease in the tick’s host ranges. Apart from the natural habitats,
ticks lose their hosts. Elk (Alces alces), the most important host for adult ticks, was
completely eradicated from the bigger part of Europe, and deer and wild boars remain rare
[27]. However, this assumption is not indemonstrable; intensive human activity has played a
role in the bigger part of D. reticulatus’ range and did not cause their elimination. Moreover,
it is not possible to establish the moment of the potential retirement of the D. reticulatus tick
from the areas of eastern Germany, western Poland and Slovakia, and which factors influence
this, because the first study on their occurrence dates from the second part of the 19th century
[57].
Although there are no geographic barriers, the division of D. reticulatus’ range ties in
with the climatic structure of Europe. On the Polish territory, the transitional area between
oceanic and continental climates is located. In this area, the moist air masses ingoing from the
Atlantic are met with dry air masses of the continental derive [58]. This fact influences the
vegetable cover and associated animals. Consequently, in Poland, there is a transitional zone
between plant communities and fauna typical for oceanic climate, represented by deciduous
forests and the communities occurred in coniferous forests, typical for continental climate.
Through the centre of Poland run range borders of the number of species of animals and
plants. It is estimated that 52% of species occurring in Poland have the transitional character,
6
which means they are spread both in the West and East; the rest of the species living in this
country are at the western or eastern borders of the occurrence [59].
These potential reasons are insufficient to explain the divided area of occurrence of the
D. reticulatus tick, because the border of their eastern occurrence area lies in the Polish
territory, and it also occurs in Western Europe.
Another potential source of the divided occurrence area can be associated with the D.
reticulatus biology and changeable climatic influence. This tick occurs in open areas; the
fluctuations in the weather in temperate zones cause large variations in temperature, humidity
and insulation levels. The sum of soil surface temperatures limits the oviposition and egg
development, and with both the required humidity and susceptibility of larvae and nymphs to
the unfavourable factors, this restricts the reproductive period to one or two months [16]. This
character of the D. reticulatus tick shows the dependence of their occurrence or local absence
with indigenous climatic conditions. It is possible to associate the divided occurrence area
with the presence of five climatic regions of Europe established by Smolec [60]. The regions
are variable, in accordance to the season; therefore, separate regions have been established for
the whole year, for cold seasons and for the vegetable season. It is evident that the area of
absence of D. reticulatus in eastern Germany and western Poland ties in with the C region for
the cold season. It is a region with warm temperatures, with the mean January temperature
being 0C, with a range from -5 to +5C. The eastern part of Poland belongs to the D region,
which is fairly cool.
The thermal conditions have the greatest influence on the overwintering ability of
many invertebrates, among them, ticks. Less is known about the influence of low
temperatures on various aspects of ticks’ biology; however, many authors suggest that ticks
are not freeze tolerant. Dautel and Knülle [61] estimated the supercooling points of European
tick species to be between -17 and -23ºC, which is the same for D. reticulatus tick; such low
temperatures limit survival. Ticks spend the winter behind in the litter, covers and other safe
places of the soil surface. The soil surface temperature depends on the insulation as well as
from the snow cover thickness. The snow cover forms the thermal conditions of the ground,
and their heat-insulating attributes, among them the small thermal conductivity, protect small
overwintering organisms (animals and plants) from the frozen habitat. On frozen days, the
soil can be frozen to the high deepness, where there is no or thin snow cover; however, when
the snow cover has a thickness of 9 cm, the frozenness occurs to 12 cm, in the thickness of 26
cm to 0.5 cm only [62]. The next important factor is the number of days with thick snow
7
cover. The moment of snow cover disappearance modulates the moment at which the
temperature rises above 0°C, through the loss of heat to the process of snow melting and
sublimation. These processes move the beginning of the growing season as well as dates of
several phonological appearances of plants [63] and also periods of animal activities,
dependent on the vegetation.
The eastern part of Poland is characterised with thick snow cover; this fact protects the
stable conditions for overwintering organisms and protects against freezing. In the western
part of Poland, the snow cover is too thin to allow protection against frost. Instead, in Western
Europe, the number of frozen days is low [62], and ticks can overwinter without snow cover
protection. With regard to the limited ability of eggs and juvenile individuals of ticks to
survive of the winter under conditions of central Europe, Dautel et al. [51] also investigated.
5. The potential reasons for the D. reticulatus tick expansion
Recently, changes in the occurrence area of many plant and animal species have been
observed. Among them, many tick species change the area, apart from D. reticulatus, in
which such phenomena is observed in the case of Ixodes ricinus and Haemaphysalis spp. ticks
[38, 64] The reasons for the expansion of D. reticulatus, such as other tick species, to new
areas, are currently not clear. It is possible to distinguish two groups of reasons. The first are
natural factors, mainly climatic, such as temperature changes, the direction of the winds and
changes in precipitation. The second sources of change are associated with human activity,
such as migrations, travels and trade [65]. Therefore, the hypotheses explaining the sources of
the previously present gap in the occurrence area can all be rebutted.
5a. Global warming
The majority of hypotheses direct the global climate warming [51]. The climatic changes
observed in last decades encompass the changes in atmospheric gas composition, average
climate and climate variability. The most spectacular symptoms noted in central Europe are
the moving of the sub-oceanic climatic region to the east, the mean winter temperature
increase, the simultaneous decline in the number of frozen days and the earlier appearance of
snow cover with shorter persistence in lowlands. The trends in indices of daily temperature
increase in temperature variability and the tendency for the number of hot days to increase
and for the number of frosty days to decrease [66, 67, 68]. A 1.5-2.5C rise of the mean
temperatures in northern Europe was observed in recent years. These changes influence the
life cycles of ticks; the effects can be activity decreases or increases, changes in the
8
population density and changes in the distribution [16]. The D. reticulatus tick belongs to
animals that are particularly susceptible to climatic factors. The threshold temperature and
humidity for their activity are relatively low. Their spring activity starts just in a moment of
snow cover disappearance at 2-4ºC, and during mid-winter it is possible to find active ticks in
January and February [69, 70, 71]. The warming especially favours the overwintering of
young developmental stages and elongates the activity period of adults. As a consequence, it
is possible to stay the spread of ticks to new areas, where unfavourable conditions
predominate [53]. For example, such a potential role was observed during the last 50 years
with regard to changes in the thickness and duration of snow cover. According to Bednorz
[62], in the second part of the 20th century, there was an increase in the number of days with
snowfall, and a tendency to reduce their thickness, such as their duration. In northern
Germany, the winters with no snowfalls and frozen days are noticed; these are the areas
presently expanded by D. reticulatus ticks. In Polish lowland territory, a similar trend was
observed. The areas that were previously potentially unfavourable for these ticks, presently
remain possible to be inhabited. Instead, on the sub-mountain areas and in the north-eastern
part of Poland, the tendency for the snow cover thickness to grow with the simultaneous
decline of frozen days was observed [68]. These factors protect the eastern populations
against the danger associated with the moving of the C thermal zone to the east. The impact of
winter temperatures on tick distribution was also highlighted by Lindgren et al. [72], in
particular in the case of Ixodes ricinus density and their northward expansion in Sweden.
5b. The influence of human activities
The term “global change” describes the climatic changes encompassing changes in
land use and land cover in response to increased consumption and population growth by
humans. Deforestation, irrigation, grazing, urbanisation etc. have the potential to change the
dynamics and geographical distribution of species, including microbial pathogens and their
vectors.
The D. reticulatus population increase and expansion are potentially caused by human
activity as well. Agriculture and farming have special influence. The last two decades of the
20th century in central Europe was a time of reform in politics and the economy, which caused
changes in agricultural practice, local reforestations, and a reduction in applied pesticides and
the number of cattle. Some of these factors can be favourable for the spread of the D.
reticulatus tick. Until the 1970s, the D. reticulatus tick was the most numerous in the former
Olsztyn and Białystok voivodeships (north-eastern Poland). In these regions, there are the
9
biggest forest complexes and the lowest cultivated areas; moreover, wide areas were assigned
to forestation. Moreover, among cultivated areas, the biggest percent were the greenlands as
well as fallows [73].
From the beginning of the 1990s, the agricultural structure changed in the whole
country. The liquidation of great state-holdings took place to the interest of individual
smallholdings. Accompanying this, there was a decrease of the general surface of agrarian
uses, with the extension of the area of fallow lands and fallows, from 163 thousand hectares in
1990 to 230 thousand in 2002 and 140 thousand in 2006. Besides, the use of fertilisers and
pesticides decreased. An essential feature of Polish agriculture is the distinct fragmentation of
farming after the system transformation. At present, above 60% of holdings do not exceed 5
hectares in size; from this, the majority is fragmented on small lots, divided by fallows and
strands of thicket [74].
5c. The management of protected areas and nature reserves
The changes in agriculture follows the intentional transformation of considerable
agrarian grounds into meadows and wooded grounds, as well as the enlargement of the
protected zones. The purpose of these actions is the restitution and enlargement of the
population of wild large mammals and birds. This secures the living conditions not only for
animals being the object of protection, but also for hundreds of other species of plants and
animals, including invertebrates, and amongst them, ticks. Although their occurrence does not
directly depend on particular species of plants, ticks are relevant in plant assemblages capable
of forming the specific microclimate and habitats of hosts.
The dense vegetation assemblages ensure that the conditions are relatively stable and
free-standing from the magnitude of the temperature, humidity and other meteorological
factors. Thus, these are essential for the survival and development of young stages of ticks.
Man, restoring the primeval phytocoenoses, also reconstitutes suitable conditions for ticks
[16, 51, 75]. Moreover, the reconstituted populations of medium-sized and large mammals are
not only the food source; they also provide the opportunity for moving to new areas. There is
a rule that young mammals leave their birthplace and migrate in search of new areas in the
autumn. Simultaneously, they transport ticks attached to their body. For D. reticulatus ticks,
such effect can occur in winter months, when the ticks are attached to the skin of elks, bison
and possibly other large mammals [70, 76].
The modern trend in environmental protection is the connection of big forest
complexes and protected areas with lines of areas disabled from human activity. The creation
10
of such ecological corridors is favourable for the expansion of many animal species, among
them ticks. The lines of afforestations in the agglomerations, as well as the great parks
containing diverse flora, are the migration route for many wild animals. With animals, the
attached ticks also migrate. The big downtown forestations make the local microclimate,
which is characterised by lower temperatures and higher humidity then built-up areas [77].
These conditions make the continuous presence of many animals within bordering towns
possible.
5d. The creation of recreational areas in towns
The special question is the presence of ticks in towns and urban agglomerations. Urban
areas are a special kind of environment, which has been strongly transformed by human
activities. The nature of human activity in towns results in the degradation of animal
associations. The characteristic feature compared to natural ecosystems is the decreasing
number of species in association and the gaining of a conspicuous numerical superiority by
one or a few species. However, a number of species are included in the associations’
composition in areas transformed by anthropopressure [78]. Parks and another green terrains,
with the presence of dense vegetation, are a suitable habitat for many species of mammals,
birds and invertebrates. The flora and fauna of parks are increasingly rich in accordance to the
size and degree of the park’s similarity to natural forest complexes. The greatest
differentiations of composition have animal associations of those environments which are
ecotones. They occur at the borders of towns and villages and at the borders of parks and
people-inhabited areas. In many cases, the forest clearings and green-keeping procedures in
big parks are intentionally reduced to settle the natural plant communities and habitats of
protected plant and animal species. In this way, parks stay desirable for wild animals, which is
typical for natural forests. For example, in big urban parks, there are commonly small and
medium sized mammals (rodents, foxes, mustelids, hares) and sometimes also large mammals
such as red and roe deer [9, 79]. The important factor is the contiguity to natural forest
complexes in the surroundings of a town. It makes the migration of mammals and other
animals from natural forests to city parks possible. With mammals, parasites, and any
attached ticks, migrate. Possibly, a large role can be played by birds, as hosts of young stages
of ticks. City parks are areas of occurrence of Ixodes ricinus ticks; however, Dermacentor
reticulatus is also present. Their occurrence in towns is recorded from Warsaw [7, 9], Kiev
[38] and [80]. It is evident that D. reticulatus has appeared in the last decade in many cases,
and often in places that were previously free of this tick [9].
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5e. Tourism and trade
The classical influence of humans on parasites’ expansion are caused by tourism, the
creation of new recreation areas, conveyance development, and enhanced welfare exchange
between countries that were previously distantly situated. The commonly known factors
include the moving of ticks by dogs, travelling with owners, and on big animals transported
within the framework of trade or farming. There are many documented cases of ticks being
brought into Poland from distant regions. Rhipicephalus sanguineus, Dermacentor
marginatus and Boophilus microplus ticks were transported by dogs from Mediterranean
countries to the Baltic region [81]. From tropical countries to Poland, ticks from Amblyomma
(Aponomma) genus migrated [82, 83]. The migrations of D. reticulatus tick into distant areas
was documented by Daugschies [84]. Also, this phenomena is not limited to the European
continent. Keirans and Durden [85] reported this species in ticks brought to the USA with
imported animals. These cases were noted in the 1960s, 1970s and 1980s, and the revealed
source was horses brought from France, among others.
6. Conclusions
To explain the phenomena of the expansion of D. reticulatus tick, it is most likely the
response of the synchronous effect of the entire combination of favourable factors for the
expansion of ticks - these include climate changes due to global warming, changes in the
landscape (the reduction of the usage of pesticides and other chemical), the growth of the
number of wildlings as a result of their protection, and the introduction of ticks into new
regions with relation to tourism and the development of conveyances.
The knowledge of ticks’ distribution and monitoring their changes are both important
from a medical and veterinary point of view. The D. reticulatus tick is known to transmit
Babesia piroplasms, Rickettsia bacteriae, Francisella tularensis and Coxiella burnetii. There
is evidence preceding the canine babesiosis records in Poland, Germany, Slovakia and
Hungary – new records and the increasing trend in the infection of dogs provided the
changing distribution of D. reticulatus ticks [16, 80, 86]. Although, this tick species does not
attack people as a rule, it is an important component of the zoonotic foci of rickettsiosis
caused by Rickettsia slovaca, R. raoultii and R. helvetica. The first records of D. reticulatus
infections with these pathogens and the first cases of human infections with
TIBOLA/DEBONEL in Poland and other countries correlate with the colonisations of new
areas and population growth [87, 88, 89, 90].
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