Microscopic and PCR findings in sheep after experimental infection with Ehrlichia phagocytophila

Methods available for the diagnosis of Ehrlichia phagocytophila infection a re limited and of low sensitivity. Since polymerase chain reaction (PCR) is a highly sensitive and specific method for the detection of infectious age nts in animals, it was considered useful to develop a PCR method specific f or this agent. An experimental protocol in which blood from 10 different ho cks was inoculated into 10 naive 1 month-old lambs was carried out. Progres s of the infection was monitored during 3 weeks by daily rectal temperature and blood samples. Eight lambs showed hyperthermia, presence of E. phagocy tophila in blood, and lower growth rate while the other two never showed th e agent in their blood or any clinical signs. This experimental infection, essentially designed to provide infected samples, also showed that flocks f rom areas previously thought to be free of E. phagocytrophila were actually infected. PCR on blood samples allowed detection of the infection earlier than in case of microscopic examination. This was related to an increased s ensitivity (87-91%). PCR yielded positive results on samples with as few as 1.08 infected neutrophils/mu l (about 0.1%). (C) 2000 Elsevier Science B.V . All rights reserved.