Multistate Survey of American Dog Ticks (Dermacentor variabilis) for Rickettsia Species

Authors

• Joy A. Hecht, Centers for Disease Control and Prevention
• Michelle E. J. Allerdice, Centers for Disease Control and Prevention
• Elizabeth A. Dykstra, Washington State Department of Health
• Laura Mastel, North Dakota Department of Health
• Rebecca J. Eisen, Centers for Disease Control and Prevention
• Tammi L. Johnson, Centers for Disease Control and Prevention
• Holly D. Gaff, Old Dominion University
• Andrea S. Varela-Stokes, Mississippi State University
• Jerome Goddard, Mississippi State University
• Benedict B. Pagac, Public Health Command-Atlantic
• Christopher D. Paddock, Centers for Disease Control and Prevention
• Sandor E. Karpathy, Centers for Disease Control and Prevention

ORCID

Goddard: https://orcid.org/0000-0002-2617-7141

MSU Affiliation

College of Veterinary Medicine; Department of Basic Sciences; College of Agriculture and Life Sciences; Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology

Creation Date

2026-09-30

Abstract

Dermacentor variabilis, a common human-biting tick found throughout the eastern half and along the west coast of the United States, is a vector of multiple bacterial pathogens. Historically, D. variabilis has been considered a primary vector of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever. A total of 883 adult D. variabilis, collected between 2012 and 2017 from various locations in 12 states across the United States, were screened for rickettsial DNA. Tick extracts were evaluated using three real-time PCR assays; an R. rickettsii-specific assay, a Rickettsia bellii-specific assay, and a Rickettsia genus-specific assay. Sequencing of ompA gene amplicons generated using a seminested PCR assay was used to determine the rickettsial species present in positive samples not already identified by species-specific real-time assays. A total of 87 (9.9%) tick extracts contained R. bellii DNA and 203 (23%) contained DNA of other rickettsial species, including 47 (5.3%) with Rickettsia montanensis, 11 (1.2%) with Rickettsia amblyommatis, 2 (0.2%) with Rickettsia rhipicephali, and 3 (0.3%) with Rickettsia parkeri. Only 1 (0.1%) tick extract contained DNA of R. rickettsii. These data support multiple other contemporary studies that indicate infrequent detection of R. rickettsii in D. variabilis in North America.

Keywords

Dermacentor variabilis; American dog tick; Rickettsia rickettsii; Rickettsia bellii; Rickettsia parkeri; Rickettsia montanensis

Publication Date

4-3-2019

Publication Title

Vector Borne and Zoonotic Diseases

Publisher

SAGE Publications; Mary Ann Liebert

First Page

652

Last Page

657

Rights

Copyright 2019, Mary Ann Liebert, Inc.

Recommended Citation

Hecht JA, Allerdice MEJ, Dykstra EA, et al. Multistate Survey of American Dog Ticks (Dermacentor variabilis) for Rickettsia Species. Vector-Borne and Zoonotic Diseases. 2019;19(9):652-657. doi:10.1089/vbz.2018.2415