Hepatozoon infections in dogs and cats in USA: History, life cycle, and suggestions for uniform terminology for hepatozoonosis in endotherms and ectotherms

Hepatozoonosis can cause serious illness in dogs in the USA resulting in muscle weakness and bone deformities. It is often fatal, and treatment is expensive and not curative. There are two recognized species of Hepatozoon which infect dogs, Hepatozoon canis and Hepatozoon americanum, transmitted by ticks, Rhipicephalus sanguineus sensu lato and Amyboloma maculatum, respectively. Hepatozoon canis has worldwide distribution and H. americanum is currently confined to the USA. Wildlife reservoirs of H. americanum have not been established but coyote (Canis latrans) is suspected, and infection is common. Most cases of hepatozoonosis in dogs in USA are thought to be due to H. americanum. However, molecular evidence suggests that a minor portion of cases in dogs are due to H. canis, sometimes as coinfection. Hepatozoonosis in domestic and wild felids, caused by Hepatozoon felis and Hepatozoon silvestris, but also H. canis, has been reported from several countries but little is known of its occurrence in domestic cats or wild felids in the USA. Here, life cycle stages of Hespatozoon spp. in dogs are compared and illustrated. Recently, a new species of Hepatozoon, Hepatozoon rufi, was described from bobcats in Mississippi, USA. There is considerable confusion concerning the terminology for different developmental stages in the life cycle of mammalian Hepatozoon spp. Here, the authors review hepatozoonosis in dogs and cats in the USA and propose a uniform terminology for the life cycle stages.