Hepatozoonosis is caused by species of the apicomplexan parasites Hepatozoon spp., belonging to the family Hepatozoidae, which parasitise leukocytes of the host animal. Unlike most other vector-borne diseases, Hepatozoon spp. are transmitted to new animals by ingestion of an infected vector. Additionally, besides the ingestion of a final arthropod host containing mature life cycle stages by the vertebrate intermediate host, other modes of transmission such as predation of one vertebrate upon another infected vertebrate host has also been observed in this genus.

Canine hepatozoonosis may present as a usually milder disease, caused by Hepatozoon canis, or a severe disease leading to debilitation and death, when caused by Hepatozoon americanum. Feline hepatozoonosis caused by Hepatozoon felis is mostly subclinical with a high proportion of cats that appear to be infected with no overt clinical signs. The pathogens do not possess zoonotic potential.


Canine hepatozoonosis is a tick-transmitted disease caused by species of the intraleukocytic parasite Hepatozoon sp., an apicomplexan protozoa of the family Hepatozoidae. Hepatozoon sp. is transmitted by ingestion of an infected arthropod vector. The parasites have an ellipsoidal shape and are about 11 x 4 µm in size.

Hepatozoon canis commonly infects dogs in tropical, subtropical and temperate regions worldwide with the Brown Dog tick, Rhipicephalus sanguineus, as major vector. Infection of dogs was originally reported from the Old World, but more recently also from South and North America. In the Southern USA a separate species, Hepatozoon americanum, causes disease in dogs and is transmitted by the tick Amblyomma maculatum.

Regarding feline hepatozoonosis, the classification of the Hepatozoon parasites found in domestic cats has longtime been uncertain, but molecular techniques identified a species distinct from H. canis, which was designated Hepatozoon felis (Criado-Fornelio et al., 2006; Ortuño et al., 2008) and has been confirmed later also in studies by Baneth et al. (2013). However, there is also evidence that H. canis can infect cats (e.g., Baneth et al., 2013).




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