Transmission of Hepatozoon canis to dogs by naturally-fed or percutaneously-injected Rhipicephalus sanguineus ticks

Hepatozoon canis is an apicomplexan protozoan parasite of dogs, prevalent i n Asia, Africa, and southern Europe. Experimental transmission of H. canis to dogs was performed with laboratory-reared Rhipicephalus sanguineus nymph s that fed on a naturally infected dog or were percutaneously injected with canine blood containing H, canis gamonts. Dogs were inoculated by oral ing estion of adult ticks containing H. canis oocysts. Transstadial transmissio n of H. canis was recorded, whereas transovarial transmission could not be demonstrated. Oocysts were detected in 85% of the adult ticks that had engo rged as nymphs on an infected dog and in 61% of the adult ticks resulting f rom nymphs injected percutaneously with blood from the same dog. Nine of 12 dogs (75%) inoculated with naturally fed or percutaneously injected ticks became parasitologically positive, and all showed seroconversion. Meronts w ere initially detected in the bone marrow 13 days postinoculation and gamon ts 28 days after infection. The variation in the time of initial detection of parasitemia among infected dogs and the rapid appearance of gamonts in d ogs immunosuppressed with corticosteroids suggest that immune mechanisms pl ay an important role in controlling H. canis parasitism. The artificial acq uisition of Hepatozoon parasites by percutaneous injection of ticks, demons trated here for the first time, may serve as a useful tool for studies on t ransmission, vector-host relationships, and the immunology of infection wit h Hepatozoon species.