The Spatial Distribution ofDermacentorTicks (Ixodidae) in Germany-Evidence of a Continuing Spread ofDermacentor reticulatus

In Europe, two tick species of the genusDermacentoroccur,Dermacentor marginatusandDermacentor reticulatus. When the spatial distribution of both species in Germany was studied comprehensively for the first time in 1976,D. marginatuspopulations were recorded along the Rhine and Main river valleys in southwestern Germany, whileD. reticulatuswas very rare. In the last 50 years, however, a considerable range expansion ofD. reticulatushas been noted in several European countries. To assess the current distribution ofDermacentorspp. in Germany, citizens were asked to send in ticks suspected to belong to the genusDermacentoror that were of unusual appearance. From February 2019 until February 2020, 3,902Dermacentorticks were received in total. Of those, 15.48% (604/3,902) were identified asD. marginatusand 84.24% (3,287/3,902) asD. reticulatus, while 11 specimens could not be identified to species level. The majority ofD. reticulatusspecimens was collected from dogs (1,212/2,535; 47.12%), whileD. marginatuswas mostly collected from horses (184/526; 34.98%). Our results confirm that the adults of bothDermacentorspecies are active all year round.D. reticulatusspecimens were sent in from all federal states except the Free and Hanseatic City of Hamburg, whileD. marginatusspecimens were only received from locations in southwestern Germany. Overall, data obtained from this citizen-science study show thatD. reticulatushas significantly expanded its range, especially in northern Germany. RegardingD. marginatus, new locations northwest of the previous range were detected, although the distribution has remained rather stable as compared toD. reticulatus. The spread ofD. reticulatus, the vector ofBabesia canis, is of major importance for veterinarians and dog owners in terms of canine babesiosis outbreaks or endemization in hithertoB. 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 extendedD. reticulatusrange and appropriate control measures.