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Throughout North America, Dermacentorspp. ticks are often found feeding on animals and humans, and are known to transmit pathogens, including the Rocky Mountain spotted fever agent. To better define the identity and distribution of Dermacentorspp. removed from dogs and cats in the United States, ticks submitted from 1,457 dogs (n= 2,924 ticks) and 137 cats (n= 209 ticks) from veterinary practices in 44/50 states from February 2018-January 2020 were identified morphologically (n= 3,133); the identity of ticks from regions where Dermacentor andersoni(Stiles) have been reported, and a subset of ticks from other regions, were confirmed molecularly through amplification and sequencing of the ITS2 region and a 16S rRNA gene fragment. Of the ticks submitted, 99.3% (3,112/3,133) were Dermacentor variabilis(Say), 0.4% (12/3,133) were D. andersoni, and 0.3% (9/3,133) were Dermacentor albipictus(Packard). While translocation of pets prior to tick removal cannot be discounted, the majority (106/122; 87%) of Dermacentorspp. ticks removed from dogs and cats in six Rocky Mountain states (Montana, Idaho, Wyoming, Nevada, Utah, and Colorado) were D. variabilis, suggesting this species may be more widespread in the western United States than is currently recognized, or that D. andersoni, if still common in the region, preferentially feeds on hosts other than dogs and cats. Together, these data support the interpretation that D. variabilisis the predominant Dermacentorspecies found on pets throughout the United States, a finding that may reflect recent shifts in tick distribution.

•Francisellaceae most abundant bacterial family in Dermacentor variabilismicrobiome.•Rickettsiaspp. identified in approximately one in five Dermacentor variabilis.•Male Dermacentor variabilisexhibit higher levels of α diversity than females.•Distinct community structure patterns in western and northeastern Dermacentor variabilis.•Apparent co-occurrence patterns between specific bacterial genera.