Tropical Canine Pancytopenia: in Vitro Cultivation of the Causative Agent—Ehrlichia canis

Abstract

SUMMARY Ehrlichia canis , causative agent of tropical canine pancytopenia ( tcp ), has been propagated in monocyte cell cultures derived from the blood of dogs acutely infected with this agent. Tissue culture medium consisted of Eagle's minimum essential medium supplemented with 20% canine serum. Results of microscopic examination of monolayers stained by Giemsa and fluorescent antibody ( fa ) methods indicated that the intracytoplasmic ehrlichia underwent a specific cycle of development. Principal developmental forms were elementary bodies (individual ehrlichia organisms), initial bodies (immature organismal inclusions), and morulae (mature organismal inclusions). Five dogs each inoculated with 2- to 8-ml. volumes of cell culture suspensions harvested on days 5, 7, 20, 23, and 28 of incubation developed signs of tcp . The organism was reisolated from these dogs. Because developmental cycle of ehrlichia demonstrated in the present study closely resembled that of the agents belonging to psittacosis-lymphogranuloma venereum ( plv ) group of agents, and because the latter agents have also been found in ticks, reclassification of the agent from family Rickettsiaceae to family Chlamydiaceae has been suggested. This work is considered a significant prerequisite for assays of fundamental properties of the organism, and it has all the essentials which would allow development of immunizing and diagnostic reagents for tcp .