title: Growth of Ehrlichia canis, the causative agent of canine monocytic ehrlichiosis, in vector and non-vector ixodid tick cell lines.
abstract: Canine monocytic ehrlichiosis is caused by Ehrlichia canis, a small gram-negative coccoid bacterium that infects circulating monocytes. The disease is transmitted by the brown dog tick Rhipicephalus sanguineus s.l. and is acknowledged as an important infectious disease of dogs and other members of the family Canidae worldwide. E. canis is routinely cultured in vitro in the canine monocyte-macrophage cell line DH82 and in non-vector Ixodes scapularis tick cell lines, but not in cells derived from its natural vector. Here we report infection and limited propagation of E. canis in the tick cell line RSE8 derived from the vector R. sanguineus s.l., and successful propagation through six passages in a cell line derived from the experimental vector Dermacentor variabilis. In addition, using bacteria semi-purified from I. scapularis cells we attempted to infect a panel of cell lines derived from non-vector species of the tick genera Amblyomma, Dermacentor, Hyalomma, Ixodes and Rhipicephalus with E. canis and, for comparison, the closely-related Ehrlichia ruminantium, causative agent of heartwater in ruminants. Amblyomma and non-vector Dermacentor spp. cell lines appeared refractory to infection with E. canis but supported growth of E. ruminantium, while some, but not all, cell lines derived from Hyalomma, Ixodes and Rhipicephalus spp. ticks supported growth of both pathogens. We also illustrated and compared the ultrastructural morphology of E. canis in DH82, RSE8 and I. scapularis IDE8 cells. This study confirms that E. canis, like E. ruminantium, is able to grow not only in cell lines derived from natural and experimental tick vectors but also in a wide range of other cell lines derived from tick species not known to transmit this pathogen.
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, UK.
authors.forename: Joana
authors.initials: J
authors.lastname: Ferrolho
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, UK.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Simpson
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, UK.
authors.forename: Philippa
authors.initials: P
authors.lastname: Hawes
authors.affiliation: Institute for Comparative Tropical Medicine and Parasitology, Ludwig-Maximilians-Universität (LMU) München, Germany; Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Onderstepoort 0110, South Africa.
authors.forename: Erich
authors.initials: E
authors.lastname: Zweygarth
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, UK. Electronic address: lesley.sakyi@pirbright.ac.uk.
authors.forename: Lesley
authors.initials: L
authors.lastname: Bell-Sakyi
mesh_terms: D000818:Animals; D001431:Bacteriological Techniques / Q000379:methods; D002460:Cell Line; D041061:Ehrlichia canis / Q000254:growth & development*; D058507:Host Specificity; D026863:Ixodidae / Q000382:microbiology*; D010274:Parasitology / Q000379:methods
keywords: Dermacentor variabilis; Ehrlichia canis; Ehrlichia ruminantium; Electron microscopy; Rhipicephalus sanguineus s.l.; Tick cell lines
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