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 in Asia, Africa, and southern Europe. Experimental transmission of H. canis to dogs was performed with laboratory-reared Rhipicephalus sanguineus nymphs that fed on a naturally infected dog or were percutaneously injected with canine blood containing H. canis gamonts. Dogs were inoculated by oral ingestion of adult ticks containing H. canis oocysts. Transstadial transmission of H. canis was recorded, whereas transovarial transmission could not be demonstrated. Oocysts were detected in 85% of the adult ticks that had engorged as nymphs on an infected dog and in 61% of the adult ticks resulting from 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 were initially detected in the bone marrow 13 days postinoculation and gamonts 28 days after infection. The variation in the time of initial detection of parasitemia among infected dogs and the rapid appearance of gamonts in dogs immunosuppressed with corticosteroids suggest that immune mechanisms play an important role in controlling H. canis parasitism. The artificial acquisition of Hepatozoon parasites by percutaneous injection of ticks, demonstrated here for the first time, may serve as a useful tool for studies on transmission, vector-host relationships, and the immunology of infection with Hepatozoon species.