Dermacentor reticulatus: a vector on the rise

Abstract

Dermacentor reticulatus is a hard tick species with extraordinary biological features. It has a high reproduction rate, a rapid developmental cycle, and is also able to overcome years of unfavourable conditions. Dermacentor reticulatus can survive under water for several months and is cold-hardy even compared to other tick species. It has a wide host range: over 60 different wild and domesticated hosts are known for the three active developmental stages. Its high adaptiveness gives an edge to this tick species as shown by new data on the emergence and establishment of D. reticulatus populations throughout Europe. The tick has been the research focus of a growing number of scientists, physicians and veterinarians. Within the Web of Science database, more than a fifth of the over 700 items published on this species between 1897 and 2015 appeared in the last three years (2013-2015). Here we attempt to synthesize current knowledge on the systematics, ecology, geographical distribution and recent spread of the species and to highlight the great spectrum of possible veterinary and public health threats it poses. Canine babesiosis caused by Babesia canis is a severe leading canine vector-borne disease in many endemic areas. Although less frequently than Ixodes ricinus, D. reticulatus adults bite humans and transmit several Rickettsia spp., Omsk haemorrhagic fever virus or Tick-borne encephalitis virus. We have not solely collected and reviewed the latest and fundamental scientific papers available in primary databases but also widened our scope to books, theses, conference papers and specialists colleagues' experience where needed. Besides the dominant literature available in English, we also tried to access scientific literature in German, Russian and eastern European languages as well. We hope to inspire future research projects that are necessary to understand the basic life-cycle and ecology of this vector in order to understand and prevent disease threats. We conclude that although great strides have been made in our knowledge of the eco-epidemiology of this species, several gaps still need to be filled with basic research, targeting possible reservoir and vector roles and the key factors resulting in the observed geographical spread of D. reticulatus.

Keywords: Asia; Babesia canis; Dermacentor reticulatus; Ecology; Epidemiology; Europe; Geographical distribution; Host associations; Omsk haemorrhagic fever virus; Spread.

Fig. 1

Most important morphological characters of female Dermacentor reticulatus. a Dorsal capitulum. b Ventral coxa. c Dorsal body. d Genital aperture. 1, Porose areas shape is a broad oval (nearly circular). 2, Palp articles 2 posterior spur is present on the dorsal surface. 3, Coxae 1 gap between external and internal spurs is narrow (also the external spur is as long as the internal spur). 4, Genital aperture posterior lips have a broad U shape (this shape is truncated posteriorly). Original drawings by Alan R. Walker [13]

Fig. 2

Most important morphological characters of male Dermacentor reticulatus. a Dorsal capitulum. b Ventral body. c Dorsal body. 1, Cornua length is long. 2, Palp articles 2 posterior spur is long on the dorsal surface. 3, Coxae 1 gap between external and internal spurs is narrow (also the external spur is as long as the internal spur). 4, Lateral groove type is in the form of punctations only (there is no groove visible). 5, Trochanter 1 posterior spur is long on the dorsal surface. Original drawings by Alan R. Walker [13]

Fig. 3

Photomicrograph of female Dermacentor reticulatus. a Dorsal view. b Ventral view

Fig. 4

Photomicrograph of male Dermacentor reticulatus. a Dorsal view. b Ventral view

Fig. 5

Photomicrograph of Dermacentor reticulatus. a Larva. b Nymph

Fig. 6

Two female and a male host seeking Dermacentor reticulatus

Fig. 7

Life-cycle of Dermacentor reticulatus

Fig. 8

Geographical distribution of Dermacentor reticulatus (red area, 26) based on Kolonin [92]

Fig. 9

Geographical distribution of Dermacentor reticulatus based on the European Centre for Disease Prevention and Control (ECDC) and Vector-Net project. The map shows the current (January 2016) known distribution of the tick species in Europe at ‘regional’ administrative level (NUTS3). They are based on published historical data and confirmed data provided by experts from the respective countries as part of the Vector-Net project; see more at: http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET-maps-tick-species.aspx#sthash.ca6HyLb6.dpuf

Fig. 10

Map of georeferenced Dermacentor reticulatus locations based on Rubel et al. [93]

Fig. 11

Biological features (intrinsic factors) contributing to successful geographical spread of Dermacentor reticulatus (see details and references in the text)

Fig. 12

Extrinsic factors contributing to successful geographical spread of Dermacentor reticulatus (see details and references in text)