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The Dermacentor reticulatus tick is a main vector of Babesia canis in Europe. The risk of canine babesiosis is unpredictable, due to significant differences in the prevalence of B. canis between ticks originating from closely situated regions. This phenomenon may be explained by vertical transmission of the pathogen in a vector population. Thus, molecular techniques were applied to investigate the occurrence of transovarial transmission in D. reticulatus ticks. DNA of B. canis was detected in 20.7% (6/29) of engorged female ticks collected from dogs, in every pool of eggs laid by positive females (100%, 6/6) and in larvae hatched from these eggs. In the pools of eggs collected from two positive females (2/6; 33.3%), no larvae hatched and no embryos were observed inside the eggs. Conclusions. Transovarial transmission of B. canis can be an important mechanism supporting maintenance of the pathogen in the environment without the presence of a reservoir vertebrate host. However, the efficiency of transovarial transmission in the maintenance of B. canis in natural conditions requires further field research.

The ornate dog tick Dermacentor reticulatus is vector of several blood parasites, including Babesia canis, a causative agent of babesiosis. The geographical range of D. reticulatus in Europe is discontinuous with a gap separating eastern and western macroregions. New foci observed in several locations in western and central Europe were considered an expansion of the western population, including foci in western Poland. In the present paper we used molecular markers to identify the origins of these foci, and we compared their genetic polymorphism to D. reticulatus collected in sites situated within the eastern population. The overall polymorphism in mt 16S rDNA was low, and all sites from the western population shared the same haplotype suggesting the expansion in this area. In the marker 5.8S rDNA-ITS2 we found no differences in polymorphism between sites from eastern Poland (eastern population), and newly emerged foci in western Poland considered a putative expansion zone of the western population. However, the sites from western Poland differed considerably from nearby German site. Our results show that foci in western Poland could not have originated from D. reticulatus from the western population, as previously thought. We found that the state border following river hinders considerably gene flow between adjacent sites what suggest that natural dispersal of D. reticulatus by wildlife is unlikely, and the emergence of new foci should rather be contributed to human-associated dispersal. We propose that livestock, and pets travelling with their owners are the most probable source of new foci, and they can easily transfer ticks within a country but not between countries., (Copyright © 2017 Elsevier B.V. All rights reserved.)