Dermacentor variabilis is the Predominant Dermacentor spp. (Acari: Ixodidae) Feeding on Dogs and Cats Throughout the United States

Abstract

Throughout North America, Dermacentor spp. 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 Dermacentor spp. 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 Dermacentor spp. 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. variabilis is the predominant Dermacentor species found on pets throughout the United States, a finding that may reflect recent shifts in tick distribution.

Keywords: Dermacentor; American dog tick; cat; dog.

Graphical abstract

Fig. 1.

Number of Dermacentor variabilis (A) and Dermacentor andersoni (B) collected from dogs and cats in different states in the United States, February 2018 to January 2020. Identification was confirmed molecularly for all ticks in the western United States and for a representative subset of ticks in other regions. Analysis showed distinct sequences indicating ‘western’ D. variabilis only in the five western states denoted with an asterisk (*); all other D. variabilis sequences were identical to those previously reported from the ‘eastern’ populations of D. variabilis.

Fig. 2.

Month of collection of adult Dermacentor variabilis from dogs and cats in the Northeast (A), South (B), Midwest (C), and West (D) regions of the United States. Due to the large number of Dermacentor variabilis ticks submitted from the Midwest, the scale of the y-axis for Fig. 2C is adjusted.