Influence of environmental factors on the occurrence of Ixodes ricinus ticks in the urban locality of Brno Pisárky, Czech Republic

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1 Vol. 32, no. 1 Journal of Vector Ecology 29 Influence of environmental factors on the occurrence of Ixodes ricinus ticks in the urban locality of Brno Pisárky, Czech Republic A. Žákovská, J. Netušil, and H. Martiníková Department of Animal Physiology and Immunology, Institute of Experimental Biology, Faculty of Science, Masaryk University, Brno, Czech Republic Received 25 July 26; Accepted 11 March 27 ABSTRACT: The occurrence of Ixodes ricinus ticks was observed in the suburban locality of Brno Pisárky (South Moravia, Czech Republic) from March to November, 1996 to 22. A total of 2,813 ticks was collected. Statistical tests divided the activity of ticks into three periods during the year. The curve of seasonality had two peaks with a maximum in May and August, with a significantly larger number of specimens collected during this period compared to other months. The abundance of ticks during Spring and Autumn months was comparable. All developmental stadia of ticks were found in this locality. The number of larvae, males, and females was not significantly different, but the occurrence of nymphs was significantly greater. Except for the year 2, there were no statistically significant differences in tick abundance. Tick activity was not dependent on humidity but did vary directly with temperature. This relation had a linear character and could be described by the equation y = x. Journal of Vector Ecology 32 (1): Keyword Index: Ixodes ticks, activity, statistical evaluation. INTRODUCTION Ticks are among the most widely distributed bloodsucking arthropods in nature. Their main threat to humans is in their role as vectors of various pathogens, the most important in the European region being tick-borne encephalitis and Lyme borreliosis (LB) (Lane et al. 1991, Hudson et al. 21, Rizzoli et al. 24, Gunther and Haglund 25, Jensen and Jespersen 25, Stanek 25, Voight 26). LB is transferred mainly by Ixodes sp. (Anderson 1989, Grubhoffer et al. 25, Taft et al. 25). In Europe, the tick Ixodes ricinus predominates (Bennett 1995, Gern 25). In this study we focused on observations of the occurrence and activity of the tick species in one chosen locality in Brno, Czech Republic. We also tested the potential effect of some ambient conditions on their abundance. The observations provide additional knowledge about the ecology of these vectors in their natural foci with a potential importance for the prevention of tick-borne diseases. MATERIALS AND METHODS Features of the locality The urban park Brno-Pisárky is located at a distance of 2 km from the city center and serves as a recreation city area. Its altitude is m above sea level and forms the bottom of the Pisárky Valley. The deciduous forests represent the predominant local vegetation along with Carpinus betulus or Quercus species, and rarely Fagus sylvatica, Betula verrucosa, or Robinia pseudoaccacia. Of coniferous species, Pinus silvestris prevails. Shrubs, such as Sambucus sp. or Crataegus sp., are complementary to the local woody species. Pulmonaria officinalis, Corydalis cava, Impatiens parviflora, or Anemome ranunculoides are typical representatives of the herbs. The biotope also contains a wide range of small and middle-sized vertebrates and is often visited by wild sheep known as mouflons, and wild boars from a nearby deer park. Human visitors come to spend their leisure time. The flow of the Svratka River corresponds with one edge of this area, and a sports facility at the other end contributes to human use as well. Under these conditions, infected ticks could represent a real health problem in this area. Collection data Ticks were collected by the flagging method, dragging white flannel flags over low vegetation.the collecting time was one h regularly, twice a month in the morning, and all 78 collections were performed periodically from 1996 to 22. All collected ticks were placed into tubes and stored alive at 5 C until they were examined. Air temperature and humidity were also measured during the collecting times. Statistical analyses The normality of data was verified using the Kolmogorov-Smirnov test. Because it was found that the series do not rise from a normal distribution, a Kruskal- Wallis test was used to test the hypothesis that all the distributions were identical. A two-choice Wilcoxon test was used for verification of the hypothesis that two independent random choices arose from the same distribution. A binomic test was applied when it was necessary to prove if the ratios obtained independently in two series were statistically different. We also used the Spearmen correlation coefficient, which does not require two-dimensional data normality. Using regression analysis, we identified the function that

2 3 Journal of Vector Ecology June 27 Table 1. Descriptive statistics of overall tick activity. Valid N Mean Median Sum Minimum Maximum Std.Dev. Total best described the relationship, and we chose the linear regression model (Benedík 1989, Souček 2). 3). DISCUSSION RESULTS A total of 2,813 ticks was collected during 78 attempts from 1996 to 22. The number of ticks in single collections ranged from 1 to 119, with a mean number of 36 (Table 1). The ticks were collected from March to November and their annual activity could be divided into three periods on the basis of statistical evaluation: Spring (March- April), Summer (May-August), and Autumn (September- November). The curve of seasonal abundance had two main peaks (677 individuals in May and 54 in August) (Figure 1). The abundance was comparable in Spring and Autumn but significantly increased in Summer. There were no statistical differences in numbers between single years as well except for 2 (Table 2). The rate of collected developmental stages was: nymphs, 67.3%, larvae, 11.2%, males, 1.7%, and females, 1.8% (Table 3, Figure 2). The influence of atmospherical conditions on the activity of ticks was also tested. The activity was not dependent on humidity but was directly correlated with temperature (Table 4). This dependence could be described by the function, y = x, which was obtained with regression analysis (Figure The activity of Ixodes ricinus was examined in the Pisárky locality in the suburban area of Brno, Czech Republic. The ticks were collected from March to November and their local annual activity averaged 22 days. This value corresponds to the generally observed period of days (Rosický et al. 1979). According to the statistical tests used, tick activity during the year could be divided into three periods: Spring (March and April), Summer (from May to August), and Autumn (September and November). Their occurence had two peaks with a maximum in May (677 individuals) and a lower peak in August (54 individuals). The abundance in Spring and Summer was comparable. This corresponded to the work of others where two peaks of activity were also registered (Rosický et al. 1979, Peťko et al. 1996, Siuda 1996). A similar result was also obtained while observing the activity of another Ixodes sp., Ixodes persulcatus (Kollars et al. 1999). A total of 2,813 ticks during 78 collections from 1996 to 22 were gathered, with the number of individuals in single collections fluctuating in a range from 1 to 119 (mean = 36). Collections of 1 to 2 captured ticks predominated (19%). Except in 2, we did not find any significant differences Number of ticks Date Figure 1. Time series representing number of ticks. Peak collections were in May and June. In 22 the number of ticks was extremely high.

3 Vol. 32, no. 1 Journal of Vector Ecology 31 Table 2. Descriptive statistics of tick numbers in particular collection years. The letters in the first column identify years in which the we did not reject the null hypothesis (a=.5). Year Valid No. of ticks Median Mean Confid. Confid. Std. Dev. No. examined 95% 95% 1996 A * A A A A A Table 3. Representation of developmental stages in percent. Letters indicate the developmental stages for which we did not rejec hypothesis (a=.5). Larvae Nymphs Males Females Total No. examined % 11.2 A A 1.8 A 1. between tick numbers in single years. All developmental stages occured in the Pisárky forest park, where nymphs heavily prevailed (67.3%). Larvae (11.2%), females (1.8%), and males (1.7%) were represented by identical numbers and this mutual ratio of single stages throughout the year did not change. The annual prevalence of nymphs in tick populations was also observed by some other authors (Gilot et al. 1996). In contrast, a marked lack of nymphal stages was noticed during another study performed in a different area (Estrada-Pena et al. 25). Ticks were collected from rodents during this investigation and not from the vegetation, and this could have had some effect on the results. The impact of climate conditions on the abundance of Ixodes ricinus was also a part of our study. The dependence of tick occurence on various climatic conditions was already investigated and reliably confirmed (Alekseev and Dubinina 2, Materna et al. 25). Ticks generally need a high humidity to compensate for any deficit in body water (Krober and Guerin 1999). Zahler and Gothe (1995) investigated the effect of temperature and humidity on longevity of another tick species, Dermacentor reticulatus. The time for 5% mortality of unfed adult ticks increased irrespective of their sex with rising relative humidity and decreasing temperature. In our case we found that humidity did not influence the occurence of ticks in investigated locality and that the activity was directly proportional to the temperature. Using regression analysis, we obtained an equation y = x, that described the dependence of abundance of ticks on ambient temperature. The mean temperature measured in this locality was 15.5 C. By substituting this into the equation, we obtained a value of 36 for the mean number of individuals per collection, confirming the configuration of the function. The temperature range from 15 to 25 C and humidity from 5 to 7% were obtained as the most suitable conditions for the tick activity in the examined area. Ticks, including Ixodes ricinus species, are related to the circulation of various pathogens in nature and their transmission to vertebrates, including humans. People should be aware of the health importance of these parasites and understand tick ecology in their natural environments. Acknowledgments This work was partially supported by MSM: REFERENCES CITED Alekseev, A.N. and H.V. Dubinina. 2. Abiotic parameters and diel and seasonal activity of Borrelia-infected and uninfected Ixodes persulcatus (Acarina: Ixodidae). J. Med. Entomol. 37: Anderson, J Epizootiology of Borrelia in Ixodes tick vector and reservoir hosts. Rev. Infect. Dis. 11: S Benedík, J Biostatistika. Univerzita. J.E. Purkyne, C.R. Brno.

4 32 Journal of Vector Ecology June Number of ticks examined Larvae Nymphs Females Males Max Min 75% 25% Median Figure 2. Box chart of tick activity regarding the developmental stages depicting the minimal and maximal amounts of collected ticks and the deviation between quartiles. 14 y=8,3+1,8*x 12 Number of ticks examined No. of ticks examined Air Temperature ( C) Figure 3. Linear regression model of the relation of tick number with temperature. The relation between tick number and ambient temperature can be described by the equation y = x.

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