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Journal of Clinical Microbiology, February 2002, p. 540-546, Vol. 40, No. 2
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.2.540-546.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Detection of Ehrlichia canis in Canine Carrier Blood and in Individual Experimentally Infected Ticks with a p30-Based PCR Assay

Roger W. Stich,^1* Yasuko Rikihisa,² S. A. Ewing,³ Glen R. Needham,⁴ Debra L. Grover,¹ and Sathaporn Jittapalapong^1,

Department of Veterinary Preventive Medicine, The Ohio State University, Columbus, Ohio 43210-1092,¹ Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio, 43210-1093,² Department of Entomology, The Ohio State University, Columbus, Ohio, 43210-12923,⁴ Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, Oklahoma 74078-2007³

Received 13 August 2001/ Accepted 18 November 2001

Detection of vector-borne pathogens is necessary for investigation of their association with vertebrate and invertebrate hosts. The ability to detect Ehrlichia spp. within individual experimentally infected ticks would be valuable for studies to evaluate the relative competence of different vector species and transmission scenarios. The purpose of this study was to develop a sensitive PCR assay based on oligonucleotide sequences from the unique Ehrlichia canis gene, p30, to facilitate studies that require monitoring this pathogen in canine and tick hosts during experimental transmission. Homologous sequences for Ehrlichia chaffeensis p28 were compared to sequences of primers derived from a sequence conserved among E. canis isolates. Criteria for primer selection included annealing scores, identity of the primers to homologous E. chaffeensis sequences, and the availability of similarly optimal primers that were nested within the target template sequence. The p30-based assay was at least 100-fold more sensitive than a previously reported nested 16S ribosomal DNA (rDNA)-based assay and did not amplify the 200-bp target amplicon from E. chaffeensis, the human granulocytic ehrlichiosis agent, or Ehrlichia muris DNA. The assay was used to detect E. canis in canine carrier blood and in experimentally infected Rhipicephalus sanguineus ticks. Optimized procedures for preparing tissues from these hosts for PCR assay are described. Our results indicated that this p30-based PCR assay will be useful for experimental investigations, that it has potential as a routine test, and that this approach to PCR assay design may be applicable to other pathogens that occur at low levels in affected hosts.

Present address: Department of Parasitology, Faculty of Veterinary Medicine, Kasetsart University, Bangkok 10900, Thailand.

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