EXPERIMENTAL TRANSMISSION OF EHRLICHIA-CANIS (RICKETTSIALES, EHRLICHIEAE) BY DERMACENTOR-VARIABILIS (ACARI, IXODIDAE)

Four trials were conducted in which laboratory-reared Dermacentor vari abilis nymphs were exposed to Ehrlichia canis by feeding on experiment ally infected dogs as soon as classical morulae were detected in perip heral blood monocytes. After molting 25, 50 or 90 adult tick pairs wer e permitted to feed on 7 Ehrlichia-naive dogs. Transmission occurred i n trials 1 (1/1 dog), 3 (1/1 dog) and 4 (2/2 dogs) but not in trial 2 (0/3 dogs), with 4 of 7 dogs becoming infected. Successful transstadia l transmission was demonstrated by detection of morulae in peripheral blood lymphocytes and by seroconversion to Ehrlichia canis 30 d post-e xposure. Incubation periods ranged between 17 and 22 days (mean = 19). Clinical signs, typical of ehrlichiosis, included mucopurulent ocular discharge, lymphadenopathy and malaise with accompanying pyrexia, leu kopenia and thrombocytopenia. Pyrexia, thrombocytopenia and erythropha gocytosis and vacuolization of the cytoplasm of monocytic cells were o bserved 1-4 d prior to detection of morulae. This is the first demonst ration that a tick other than Rhipicephalus sanguineus is capable of t ransstadial transmission of this important pathogen of dogs. (C) 1998 Elsevier Science B.V.