Canine and Feline Hepatozoonosis

Canine and Feline Hepatozoonosis

Prof. Gad Baneth, DVM, PhD, Dipl. ECVCP

Introduction:

Hepatozoonosis is a vector-borne infection caused by apicomplexan protozoa that have a vertebrate host, such as the dog or cat, and an arthropod blood-sucking vector, such as a tick. Although most tick-borne pathogens are transmitted with the vector’s saliva through its salivary glands, Hepatozoon species are different because they infect their vertebrate hosts when they swallow and consume their arthropod vectors containing mature parasite oocysts with infective sporozoites in them.

Therefore, infection is not passed during a vector’s bite, but rather when the vector itself is swallowed. In the case of Hepatozoon species that infect dogs, infection is passed when the dog swallows a tick or parts of it.

More than 340 species of Hepatozoon have been described in different vertebrate hosts ranging from amphibians, through reptiles, birds, marsupials and mammals. More than 100 species have been described in snakes. However, domestic dogs and cats are hosts to a small number of Hepatozoon species.

Two different species of Hepatozoon infect dogs, Hepatozoon canis globally, and Hepatozoon americanum in the southern USA. Clinically, H. canis infection varies between being asymptomatic in dogs with a low parasitaemia, to a severe disease with anemia, profound lethargy and cachexia in dogs with a large number of circulating parasites.

Hepatozzon americanum infection causes mainly lameness with severe musculoskeletal pain due to myosistis and periosteal bone lesions. Domestic cats have been described to be infected with three Hepatozoon species: Hepatozoon felis, Hepatozoon silvestris and H. canis. Hepatzoon felis is mostly a cause of sub-clinical infection in cats but has also been associated with clinical disease. Hepatozoon silvestris was originally described in the wild European cat Felis sivlestris, and has also been associated with a number of clinically-ill cats, and H. canis has so far only been shown to be present in cats with no clear connection to disease.