Distribution of ticks in Bosnia and Herzegovina.

Ticks are one of the important groups of parasites, whose populations have increased in Europe in the last 20 years and, as vectors of many emerging diseases, are a major threat to human and animal health. Bosnia and Herzegovina has both climate and environmental conditions favorable for ticks. Given this risk, the aim of this study was to identify tick species currently present in this country and to compare the findings with previous studies, in order to update information on their spatial distribution and other parameters of occurrence. From March 2017 to April 2020, ticks were collected in 42 sampling areas (municipalities) throughout the country. Prespecified identification keys were used for identifying the ticks to the species level. A total of 6193 tick specimens from the Ixodidae family were collected from animal hosts or from vegetation. Ixodes ricinus was the most dominant tick species found. However, our results indicate a decrease in the relative contribution of this tick species to the overall abundance of tick populations. Dermacentor marginatus, which almost doubled in abundance compared to earlier studies, is the second most common tick species. We further confirmed the presence of Dermacentor reticulatus, Rhipicephalus bursa, Rhipicephalus sanguineus sensu lato, Hyalomma marginatum and Haemaphysalis punctata. Ixodes hexagonus, Ixodes canisuga and Haemaphysalis concinna, which were previously reported at low abundance were not found amongst our specimens.

Introduction

During recent decades, environmental factors combined with constant transformation of habitats, mainly related to human activity, have modified transmission patterns of parasitic diseases (Otranto et al., 2015). Ticks are an important group of parasites whose populations have increased and expanded in Europe over recent decades (Medlock et al., 2013). An increase in the occurrence of tick-borne diseases presents a major threat to human and animal health (Danielova et al., 2008; Smith et al., 2011; Claerebout et al., 2013; Medlock et al., 2013; Otranto et al., 2015). The trends towards larger populations are, in part, due to landscape fragmentation and an increase in the abundance of hosts. This, along with warming temperatures, has enabled the development and survival of ticks over a longer period during the year (Gray, 2008; Estrada-Peña, 2008). As a result, ticks have expanded their range in Europe, both in altitude and geographical distribution (Alfredsson et al., 2017).

Understanding tick population dynamics, the seasonality of their occurrence and their vector capacity is very important in order to develop preventative measures against them and the pathogens they transmit. In the European part of the Mediterranean, 46 species (37 of the family Ixodidae and 9 of the family Argasidae) of the >900 species currently described have been identified (Guglielmone et al., 2014; Estrada-Peña et al., 2017). In the Balkan area alone, 25 tick species have been described (22 of the family Ixodidae and 3 of the family Argasidae) (Estrada-Peña et al., 2017).

The first written report on the tick fauna of Bosnia and Herzegovina (BiH) was given in 1911 by Neumann, who described species from the genus Hyalomma (Omeragic, 2011). In the 21st century, 11 species of ticks from the family Ixodidae were found in BiH, and none were found from the family Argasidae. Ixodes ricinus is considered the most common species, followed by Dermacentor marginatus, Rhipicephalus bursa, Hyalomma marginatum, Rhipicephalus sanguineus sensu lato, Haemaphysalis punctata, Ixodes canisuga, Dermacentor reticulatus, Ixodes hexagonus and Haemaphysalis concinna (Omeragic, 2008, 2011; Dmitrović et al., 2014; Krcmar et al., 2014; Omeragic et al., 2015). Ixodes hexagonus has, so far, been found only on two hunting dogs, I. canisuga has been described from several foxes, while Ha. concinna has been detected on one migratory bird.

The aim of this study was to collect ticks throughout BiH and identify tick species currently present in the country. These findings would, in turn, be compared with earlier data, to update information on their spatial distribution and other parameters of tick occurrence.

Materials and methods

Study area

Bosnia and Herzegovina is located in southeastern Europe, in the western region of the Balkan Peninsula. The country area is 51,209 km2, and it encompasses three climate zones: the Mediterranean zone (in the narrow stretch of plain near the Adriatic Sea), the Mountain zone in the central part of BiH and the Moderate continental zone in northern and eastern parts of BiH. The mean annual precipitation in the Mediterranean zone ranges from 1000 to 1800 mm. In the central and northern parts of the country this ranges 900 to 1300 mm, and in higher mountain areas there is up to 2600 mm of annual precipitation. Average annual temperatures are 12.8–15.2 °C (Mediterranean zone), 1.2–11.6 °C (Mountain zone) and 9.6–11.4 °C (Moderate zone). Also, several transitional climate areas related to altitude are recognized aside from the three main ones. The mean annual temperature for the country has risen by an average of 0.8 °C over the past century. The average temperature in the previous decade is the warmest in the last 120 years (Institute for Statistics of Federation of BiH, 2019).

Tick sampling and species determination

From March 2017 to April 2020, ticks were collected in 42 sampling areas (municipalities) located around the country. There where one or more sampling locations in each area, with a total of 96 sampling locations in the study (Fig. 1). Ticks were collected in 1–5 sampling locations in municipalities with areas of up to 500 km2. Municipalities with areas between 500 and 1000 km2 contributed samples from 6 to 10 locations. Ten or more sites were visited in municipalities which were larger than 1000 km2. Locations were visited randomly throughout the year and some more than once. All ticks found on infested animal hosts were collected using spoon-end tweezers, in order to acquire the entire tick with minimal damage. Tick sampling from vegetation in the immediate environment of the hosts was performed by flagging, using a white cloth (1 m2) flagged over vegetation. All tick stages found attached to the cloth were collected using fine tweezers.

Fig. 1

Tick sampling areas (municipalities - 42 in total) within the BiH with numbers of sampling location (96 in total) in proportion to the municipality size.

Tick sampling was done according to the technique described in the ECDC Technical report (Technical Report, 2020), which was an outcome of the VectorNet project and by Walker et al. (2014). Identification keys provided by Pomerancev (1950), Kapustin (1955), Walker et al. (2014) and Estrada-Peña et al. (2017) were used to identify the ticks to the species level. Morphological differentiation was conducted at the Laboratory for Parasitology accredited with BAS EN ISO/IEC 17,025:2018, of the Veterinary Faculty University of Sarajevo.

Results

A total of 6193 tick specimens, all from the Ixodidae family, were collected at 96 locations and identified to the species level (Table 1).

Table 1

Ixodid species collected and differentiated by host are shown in absolute numbers and in frequencies (%) relative to the total number of adult specimens collected from March 2017 to April 2020.

Species	Dogs	Cats	Cattle	Sheep	Goats	Horses	Poultry	Cham-ois*	Total	%
Ixodes ricinus	3195	148	172	156	159	28	12	3	3873	63.8
Dermacentor marginatus	840	14	121	253	18	8	0	0	1254	20.7
Dermacentor reticulatus	210	12	0	0	0	11	0	0	233	3.8
Rhipicephalusbursa	2	0	0	112	152	0	0	0	266	4.4
Rhipicephalus sanguineus sensu lato	167	0	0	0	0	0	0	0	167	2.8
Hyalomma marginatum	0	0	109	25	0	0	0	0	134	2.2
Haemaphysalis punctata	1	0	18	111	4	0	0	6	140	2.3
Total	4415	174	420	657	333	47	12	9	6067

*captured wild animals.

Table 1. Ixodid species collected and differentiated by host are shown in absolute numbers and in frequencies (%) relative to the total number of adult specimens collected from March 2017 to April 2020.

Most of the tick specimens were collected from dogs (71.3%), followed by sheep (10.6%), cattle (6.8%), goats (5.4%), cats (2.8%), horses (0.8%), poultry (0.2%) and chamois (0.2%). On average 6 tick specimens were collected from each animal host found to be tick infested, with a range of 1 to 25. Additionally, 126 ticks (in 21 out of 96 sampling locations) were collected from vegetation surrounding the immediate environment of sampled hosts, out of which 65.9% were I. ricinus and the rest D. marginatus. Most of the tick collected from hosts were adult stages (6047) out of which 63.6% were females and 34.1% males. There were 99 specimens in nymphal and 47 in larval stages (Table 2). Of the specimens collected from vegetation, 31 were nymphs and 56 larvae.

Table 2

Immature ticks found among specimens collected from March 2017 to April 2020 in absolute (by species and specimen origin) and relative frequency (%) (by species).

.Tick species	Developmental stage		Sample origin		%
	Nymph	Larva	Dog	Sheep	Nymphs	Larvae
Ixodes ricinus	69	29	23	0	69.7	61.7
Dermacentor marginatus	26	7	7	0	26.3	14.9
Haemaphysalis punctata	4	11	0	2	4.0	23.4
Total	99	47	30	2	100	100

Table 2 Immature ticks found among specimens collected from March 2017 to April 2020 in absolute (by species and specimen origin) and relative frequency (%) (by species).

Species diversity was found to be increased in the areas with higher average rainfall (western and southern parts of BiH) which contributed almost half of all ticks collected (44.76%) in the study, though they comprise less than a quarter of the area sampled (12 out of 42 sampling areas).

Of the established ticks species, only I. ricinus, D. marginatus and D. reticulatus were found at locations over 1000 m altitude. These were found primarily on dogs, with one specimen of D. marginatus found on sheep. Hyalomma marginatum were found on cattle and sheep from sampling areas of karst fields (altitude ranging from 300 to 891 m).

Discussion

Ticks species identified in this study are commonly found in the Balkan and the European part of the Mediterranean Region. Thus, Krčmar (2019) identified 7 species in various forest communities in eastern Croatia, using the dragging method and in collection from 10 different animal host species. I. ricinus accounted for almost 2/3 of the specimens, followed by D. reticulatus, D. marginatus, Ha. concinna, Ha. inermis, I. canisuga and I. hexagonus.

The distribution of developmental stages within our collections are similar with those reported by other studies (Földvari and Farkas, 2005; Smith et al., 2011; Beck et al., 2014).

Ixodes ricinus is the most dominant tick species found in BiH. However, our results indicate a decrease in the contribution of this tick species compared to earlier research in the country (Omeragic, 2008; Muftic, 1965; Delic et al., 1958). This species is the most commonly found tick in neighboring countries on hosts and by vegetation flagging (Krčmar, 2012), as well as in some other European countries (Remesar et al., 2018; Eichenberger et al., 2015; Smith et al., 2011; Nijhof et al., 2007).

Although species of the genus Ixodes are common in Europe, studies indicate an increase in their geographical distribution as well as that of other genera of ticks (Claerebout et al., 2013, Földvári et al., 2016). In some countries I. ricinus, though commonly present, is not the dominant tick species found on dogs (Maurelli et al., 2018; Földvari and Farkas, 2005; Beck et al., 2014). Many reports also indicate a surge in the occurrence of D. reticulatus (Nijhof et al., 2007; Smith et al., 2011; Claerebout et al., 2013; Krčmar, 2019, Zajac et al., 2020). This species has recently expanded its range, as a result of an increase in grassland habitats and non-cultivated agricultural land.

Within the genus Dermacentor there are 35 species known globally, of which only two are found in the Mediterranean: D. marginatus and D. reticulatus (Estrada-Peña et al., 2004; Guglielmone et al., 2014). Dermacentor marginatus is the second most commonly collected tick species in our study, with almost twice the relative contribution compared to earlier studies in the country (Omeragic, 2008). Apart from the report from 2008, there are no earlier records of D. marginatus in BiH, except from a study conducted from 2003 to 2006, where this tick was found on dogs from Sarajevo and Banjaluka (Omeragic, 2011).

Dermacentor reticulatus seems to be an expanding tick species throughout this country, as well as elsewhere in Europe (Nijhof et al., 2007; Smith et al., 2011; Claerebout et al., 2013; Krčmar, 2019; Zajac et al., 2020). Medlock et al. (2017) indicated that D. reticulatus is a common tick in some areas of the British Isles, with southern Europe being the southern limit of its range. Dermacentor reticulatus possesses resilient biological characteristics, has a wide range of hosts, a high vector capacity, and a great adaptability. These factors underline its spread across Europe (Földvári et al., 2016). They can be active during the cooler, winter months in many climate zones when low temperatures restrict activity of I. ricinus.

Ticks from the genus Rhipicephalus have been continuously present in BiH throughout the past century, particularly R. bursa, which is associated with small ruminants (Apfelbeck, 1927; Cvjetanovic, 1956; Delic et al., 1958; Zuko, 1998; Omeragic 2008, 2011). Our study indicates R. bursa is the third most common tick species (4.3%), but less common than in the study by Omeragic in 2008, where a relative contribution of 7.8% was reported. Rhipicephalus sanguineus sensu lato was found only on dogs and in frequency and is comparable in frequency to earlier studies (Apfelbeck 1927; Delic et al., 1958; Zuko 1998; Omeragic, 2008). This tick appears rarely on dogs in northern European countries such as the Netherlands and Germany according to Nijhof et al. (2007) and Beck et al. (2014). This species predominates on dogs in southern European countries, with contribution of 53% in Spain (Estrada-Peña et al., 2017) and 63.6% in Italy (Maurelli et al., 2018).

Several species of the genus Hyalomma have previously been reported. However only Hy. marginatum has been reported in the past twenty years (Omeragić, 2008, 2011). Hyalomma marginatum was first reported in BiH in 2008, with a contribution of 5.7% among specimens collected from cattle, sheep, horses and dogs (Omeragić, 2008, 2011). This ranged from 4.4% relative contribution among specimens from the central part of the country to 9.9% among specimens from the eastern part. In our study, 2.2% ticks collected were Hy. marginatum, with the specimens found on cattle and sheep. In a survey on ticks found on domestic animals (n = 2162) in Albania, Kadriaj et al. (2018) concluded that Hy. marginatum was the most commonly found tick in cattle (32.8%) and on dogs (100%), while R. bursa was the most common in sheep (81.2%) and goats (100%).

Earlier studies found Haemaphysalis punctata to be the only tick species of the genus Haemaphysalis found in BiH in specimens primarily from ruminants, without major changes in their frequency of occurrence (Omeragic, 2008, 2011; Apfelbeck, 1927; Cvjetanovic, 1956; Delic et al., 1958; Muftic 1965; Zuko 1998).

Tick species found with very low occurrence in earlier studies conducted in BiH, such as I. hexagonus, I. canisuga and Ha. concinna, did not occur amongst our specimens (Omeragic, 2008, 2011; Apfelbeck, 1927; Cvjetanovic, 1956; Delic et al., 1958; Muftic 1965; Zuko 1998).

Although there is evidence on some Ixodidae tick activity in BiH during the winter months, their occurrence is the highest during May and June, when average monthly temperatures fall between 13.0 and 20.0 °C, relative humidity surpasses 80% and average monthly rainfall is above 120 mm (Omeragic, 2008, 2011). In our study, sampling locations with relatively higher rainfall contributed most of ticks found. Tick survival and activity is related to climate parameters, most commonly increased temperature and increase in humidity. This has been reported by others (Tälleklint and Jaenson 1998; Daniel et al., 2004; Bowman and Nuttall, 2004; Danielova et al., 2008; Gray, 2008; Beck et al., 2014). Interestingly, specimens we collected from a dog in February 2019 in the Livno sampling area (altitude 730 m, 7 am and 1 pm temperature −10,2 °C and 2 °C, respectively) included several D. reticulatus ticks. The host experienced severe symptoms characteristic of babesiosis 8 days after sampling, and Babesia canis was later confirmed in a blood smear.

The average altitude in BiH is around 525 m, and 75% of the country lies below 1000 m. This provides ticks an advantage from the prevailing habitat and the availability of hosts within this altitude range, in addition to favorable climate conditions. Our results indicate an increase in tick species diversity in sampling locations over 1000 m of altitude over that found in earlier studies, which reported only I. ricinus and R. bursa at altitudes over 1000 m (Omeragic, 2008, 2011). This trend is even more evident if even earlier data are considered. In the study by Cvjetanovic (1956), I. ricinus was not found at altitudes over 800 m in BiH, while R. bursa was reported at sampling locations at altitudes of 1150 m. Delic et al. (1958) reported 13 tick species throughout the country with only Ha. punctata found at altitudes above 800 m. Comparably, Muftic (1965) reports that none of the 7 tick species identified in their study were found at altitudes higher than 900 m.

Studies conducted in the Czech Republic show an increase in the average annual and seasonal temperatures, as well as increases in rainfall, are highly correlated with increases in the population and distribution of I. ricinus. This results in more tick-borne encephalitis and other vector-borne diseases in hosts in higher altitudes (Daniel et al., 2004; Danielova et al., 2008 and Danielova et al., 2010). In these areas, an increase in the average monthly temperature of 1.5 °C during the peak of I. ricinus activity (May-August) has led to an expansion of habitats for ticks previously only found prevalent at lower altitudes (200–450 m). An increase in the average temperatures has been seen in BiH, particularly in colder climate areas and at higher altitudes, as shown in a similar Hungarian study by Széll et al. (2006). This provides a longer time period during the autumn suitable for tick activity, with there being some evidence of activity even in winter.

In addition to all other favorable conditions, the presence of greater forested areas as compared to cultivated land is another factor contributing to the occurrence and distribution of ticks in BiH. Due to poor forest management and a lack of agricultural support during recent decades, the following trends are observed: more degraded low forests, loss of over 10% forested areas and an increase in non-cultivated agricultural land (Institute for Statistics of Federation of Bosnia and Herzegovina, 2019). These trends further enhance the survival of small mammals during winters, which, along with the presence of birds, favors the development, survival and spread of ticks. In addition to climate change, other factors are becoming increasingly important regarding tick distribution, such as changes in wildlife distribution, environmental changes due to human activity and soil management and use (Medlock et al., 2013). When estimating and responding to public health risks related to ticks and tick-borne diseases, all above factors need to be considered.

Conclusion

Most tick species abundance and prevalence in recent years in BiH and other parts of Europe is on the rise, particularly in species that are carriers of various pathogens. More efforts will be needed in the future to adequately investigate and address these phenomena.

CRediT authorship contribution statement

Jasmin Omeragić: Conceptualization, Methodology, Investigation, Resources, Writing – original draft, Writing – review & editing, Project administration. Sabina Šerić – Haračić: Methodology, Methodology, Writing – original draft, Writing – review & editing. Darinka Klarić Soldo: Investigation, Writing – original draft. Naida Kapo: Investigation, Writing – original draft, Writing – review & editing. Nihad Fejzić: Resources, Project administration. Vedad Škapur: Investigation. Jolyon Medlock: Methodology, Resources, Writing – review & editing, Supervision, Project administration.

Declaration of Competing Interest

None.