Emerging parasitic infections vectored by brown dog ticks in North America

Abstract

The research conducted in this dissertation provides a better understanding of the prevalence and geographic distribution of emerging and zoonotic organisms transmitted by brown dog ticks throughout the United States. In Chapter 3, we tested skin biopsy samples from dogs in Oklahoma for evidence of Cercopithifilaria spp. infection by saline sedimentation and PCR and tested ticks collected from these animals by PCR. In this study, Cercopithifilaria bainae was detected in 6/250 (2.4%) dogs and 3 brown dog ticks, indicating that this parasite may be circulating in Oklahoma. Prior to the study outlined in Chapter 3, C. bainae had been detected in dogs and ticks in other parts of the world, with a single report in 2019 originating from the United States (Florida). In Chapter 4, we tested brown dog ticks collected from animals across the United States for molecular evidence of Cercopithifilaria spp. infection to better understand the geographic distribution of this emerging parasite on a national scale. Here, we identified C. bainae DNA in 80/1400 (5.7%) brown dog ticks collected from 55 different dogs across 11 states, suggesting a more widespread geographic distribution of the parasite within the United States than previously known. Lastly, in Chapter 5, we tested a cohort of the brown dog ticks that were tested in Chapter 4 for molecular evidence of infection with tick-borne pathogens including Babesia spp., Ehrlichia canis, and Rickettsia spp. While no Babesia spp. were detected, we did identify rickettsial agents in 24 ticks, including 1 E. canis, 3 Rickettsia amblyommatis, 11 R. massiliae, 3 R. monacensis, 5 R. montanensis, and 1 undefined Rickettsia species. The data from Chapter 5 documents E. canis in randomly sampled individual ticks and R. monacensis in brown dog ticks in the United States for the first time, and R. massiliae in new geographic regions. In summary, brown dog ticks across the United States may be harboring a variety of emerging and zoonotic infectious agents. Further research is needed to uncover the suite of organisms that brown dog ticks may harbor in the United States to inform national efforts aimed at protecting canine and human health.