Hepatozoon

(Hepatozoon canis)

Hepatozoonosis is a tick-borne apicomplexan protozoan distributed throughout the tropics and subtropics. Mild to severe disease may manifest in dogs.

Parasite: Hepatozoon canis
Common name: canine hepatozoonosis
Hosts: Dogs and wild canids
Location in host: Gamonts in cytoplasm of neutrophils and monocytes
Distribution: Tropics and subtropics, worldwide (not Australia)
Transmission route: ingestion of tick vectors
Zoonotic: No

Distribution

Two different species of Hepatozoon infect domestic dogs, H. canis in Southern Europe, Africa, Asia, Latin America and parts of the USA, and Hepatozoon americanum in the southeastern USA. H. canis is transmitted by the tick Rhipicephalus sanguineus (Fig 1) which is prevalent in tropical and sub-tropical regions and by Amblyomma ovale in South America. Transplacental transmission from dam to its pups has been demonstrated for H. canis.

Figure 1. The brown dog tick, Rhipicephalus sanguineus sensu lato. (Image credit: CDC/ James Gathany; William Nicholson.)
Figure 2. Hepatozoon canis gamont in a neutrophil of a stained capillary blood smear. (Image credit: Dr Ketsarin Kamyingkerd.)

Clinical signs

H.canis infects the hemolymphatic tissues and causes anemia and lethargy. H. canis infection varies from being subclinical in apparently healthy dogs to severe with lethargy, fever, cachexia and pale mucous membranes due to anemia.

Diagnosis

H.canis infection is frequently diagnosed by microscopic detection of intracellular H. canis gamonts in neutrophils and monocytes in stained capillary blood smears (Fig 2). The degree of parasitaemia is directly proportional to the severity of clinical signs. PCR of whole blood for H. canis detection is sensitive and specific.

Treatment

H.canis infection is treated with imidocarb dipropionate at 5-6 mg/kg IM or SC every 14 days until gamonts are no longer present in blood smears. The decrease of parasitemia is slow and usually requires several repeated imidocarb treatments.

Control

Prevention consists of the use of topical acaricides and environmental parasiticides. Furthermore, it is recommended to avoid the dog ingesting ticks while scavenging or grooming.

Public health considerations

H.canis is not zoonotic. Hepatozoon infection in humans has not been described except for a single case in which the species was not identified.