The Spatial Distribution of Dermacentor Ticks (Ixodidae) in Germany-Evidence of a Continuing Spread of Dermacentor reticulatus

Abstract

In Europe, two tick species of the genus Dermacentor occur, Dermacentor marginatus and Dermacentor reticulatus. When the spatial distribution of both species in Germany was studied comprehensively for the first time in 1976, D. marginatus populations were recorded along the Rhine and Main river valleys in southwestern Germany, while D. reticulatus was very rare. In the last 50 years, however, a considerable range expansion of D. reticulatus has been noted in several European countries. To assess the current distribution of Dermacentor spp. in Germany, citizens were asked to send in ticks suspected to belong to the genus Dermacentor or that were of "unusual" appearance. From February 2019 until February 2020, 3,902 Dermacentor ticks were received in total. Of those, 15.48% (604/3,902) were identified as D. marginatus and 84.24% (3,287/3,902) as D. reticulatus, while 11 specimens could not be identified to species level. The majority of D. reticulatus specimens was collected from dogs (1,212/2,535; 47.12%), while D. marginatus was mostly collected from horses (184/526; 34.98%). Our results confirm that the adults of both Dermacentor species are active all year round. D. reticulatus specimens were sent in from all federal states except the Free and Hanseatic City of Hamburg, while D. marginatus specimens were only received from locations in southwestern Germany. Overall, data obtained from this citizen-science study show that D. reticulatus has significantly expanded its range, especially in northern Germany. Regarding D. marginatus, new locations northwest of the previous range were detected, although the distribution has remained rather stable as compared to D. reticulatus. The spread of D. reticulatus, the vector of Babesia canis, is of major importance for veterinarians and dog owners in terms of canine babesiosis outbreaks or endemization in hitherto B. canis-free areas. Thus, veterinarians and veterinary students need to be informed about the new situation to be able to give adequate advice to dog owners on the extended D. reticulatus range and appropriate control measures.

Keywords: Dermacentor marginatus; Dermacentor reticulatus; Germany; citizen-science; range expansion; species distribution.

Figure 1

Distribution of Dermacentor reticulatus (A) and Dermacentor marginatus (B) in Germany based on ticks submitted by German citizens from February 2019 to February 2020. Only locations with medium to high accuracy are shown (D. reticulatus: N = 1,744/3,287, D. marginatus: N = 450/604). More intense colors indicate multiple findings in close proximity. Red shaded areas in (A) represent areas of D. reticulatus distribution as reported by the European Centre for Disease Prevention and Control (ECDC) in July 2019 (https://www.ecdc.europa.eu/en/publications-data/dermacentor-reticulatus-current-known-distribution-july-2019) for comparison. In the map insert, federal states are abbreviated with italic letters (B, Berlin; BR, Bremen; BW, Baden-Wuerttemberg; BV, Bavaria; BB, Brandenburg; HH, Free and Hanseatic City of Hamburg; H, Hesse; LS, Lower Saxony; MWP, Mecklenburg-Western Pomerania; NRW, North Rhine-Westphalia; RP, Rhineland-Palatinate; S, Saxony; SA, Saxony-Anhalt; SH, Schleswig-Holstein; SL, Saarland; T, Thuringia). Cities are abbreviated with bold letters (BS, Brunswick; C, Cologne; F, Freiburg; G, Gießen; H, Hanover; K, Karlsruhe; L, Leipzig; M, Mannheim; S, Stuttgart).

Figure 2

Distribution of (A) Dermacentor reticulatus (blue dots) and (B) Dermacentor marginatus (red dots) in Germany based on ticks submitted by German citizens from February 2019 to February 2020 in comparison to data from previous studies. In (A), D. reticulatus locations as reported by Rubel et al. (1) are shown in orange and those reported by Naucke (13) in green. In (B) D. marginatus locations as reported by Rubel et al. (1) are shown in yellow. More intense colors indicate multiple findings in close proximity. In the map insert, federal states are abbreviated with italic letters (B, Berlin; BR, Bremen; BW, Baden-Wuerttemberg; BV, Bavaria; BB, Brandenburg; HH, Free and Hanseatic City of Hamburg; H, Hesse; LS, Lower Saxony; MWP, Mecklenburg-Western Pomerania; NRW, North Rhine-Westphalia; RP, Rhineland-Palatinate; S, Saxony; SA, Saxony-Anhalt; SH, Schleswig-Holstein; SL, Saarland; T, Thuringia). Cities are abbreviated with bold letters (BS, Brunswick; C, Cologne; F, Freiburg; G, Gießen; H, Hanover; K, Karlsruhe; L, Leipzig; M, Mannheim; S, Stuttgart).

Figure 3

Dermacentor reticulatus (N = 2,785) and Dermacentor marginatus (N = 596) specimens by month of collection, sent in by German citizens from February 2019 to February 2020.