RESUMEN
A considerable range expansion of Dermacentor reticulatus has been observed in several European countries, which is concerning in the light of its vector function for several pathogens, including Babesia canis and tick-borne encephalitis virus (TBEV). The present study provides an update on the distribution of Dermacentor ticks in Germany, using a citizen science approach. Ticks were collected by citizens from March 2020 to May 2021, and submitted along with information on the date and location of collection, potential hosts and details about the circumstances of discovery. In total, 3,292 Dermacentor specimens were received, of which 76.4% (2,515/3,292) were identified as D. reticulatus and 23.0% (758/3,292) as D. marginatus, while 0.6% (19/3,292) were too damaged for species-level identification. Dermacentor reticulatus was received from all federal states of Germany. Maxent species distribution models predicted suitable environmental conditions for D. reticulatus throughout Germany. Findings on the vegetation or on pastured animals without travel history confirmed the occurrence of this tick species as far north as the most northern German federal state Schleswig-Holstein. In contrast, the distribution of D. marginatus still appears to be limited to southwestern Germany, although the northward shift of the distribution limit observed in the preceding citizen science study, as compared with previous published distributions, was confirmed. This shift was also predicted by Maxent species distribution models, reflecting the broader distribution of the tick occurrence data contributed by citizens. Most D. reticulatus ticks were found on dogs (1,311/1,960, 66.9%), while D. marginatus was mainly discovered on hoofed animals (197/621, 31.7%) and humans (182/621, 29.3%). Human tick bites were reported in 0.7% (14/1,960) of host-assigned D. reticulatus and 3.4% (21/621) of host-assigned D. marginatus. Further studies to investigate an increasing endemisation of Babesia canis in Germany as well as the relevance of D. reticulatus for TBEV spread throughout the country, e.g., by traveling dogs, are urgently needed. In view of the activity of D. reticulatus during winter or the colder months, which complements that of Ixodes ricinus, a year-round tick protection of at least dogs is strongly recommended.
RESUMEN
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.