摘要：

Canine monocytic ehrlichiosis is caused byEhrlichia canis, a small gram-negative coccoid bacterium that infects circulating monocytes. The disease is transmitted by the brown dog tickRhipicephalus sanguineuss.l. and is acknowledged as an important infectious disease of dogs and other members of the family Canidae worldwide.E. canisis routinely culturedin vitroin the canine monocyte-macrophage cell line DH82 and in non-vectorIxodes scapularistick cell lines, but not in cells derived from its natural vector. Here we report infection and limited propagation ofE. canisin the tick cell line RSE8 derived from the vectorR. sanguineuss.l., and successful propagation through six passages in a cell line derived from the experimental vectorDermacentor variabilis. In addition, using bacteria semi-purified fromI. scapulariscells we attempted to infect a panel of cell lines derived from non-vector species of the tick generaAmblyomma,Dermacentor,Hyalomma,IxodesandRhipicephaluswithE. canisand, for comparison, the closely-relatedEhrlichia ruminantium, causative agent of heartwater in ruminants.Amblyommaand non-vectorDermacentorspp. cell lines appeared refractory to infection withE. canisbut supported growth ofE. ruminantium, while some, but not all, cell lines derived fromHyalomma,IxodesandRhipicephalusspp. ticks supported growth of both pathogens. We also illustrated and compared the ultrastructural morphology ofE. canisin DH82, RSE8 andI. scapularisIDE8 cells. This study confirms thatE. canis, likeE. 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.

展开