Nancy Vincent-Johnson, Gad Baneth, Kelly E. Allen

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

1 Scopus citations


• Cause: Hepatozoonosis is an arthropod-borne infection caused by apicomplexan protozoa from the family Hepatozoidae in the suborder Adeleorina. Based on DNA analysis of the gene encoding for 18S rRNA and morphologic features, parasites in the genus Hepatozoon are most closely related to other apicomplexan parasites such as Plasmodium spp. and piroplasms. The genus was named Hepatozoon because merogonic development of the type strain Hepatozoon muris was observed in rat livers. However, the liver is not necessarily a major target tissue for other Hepatozoon spp. More than 300 Hepatozoon species have been described in amphibians, reptiles, birds, marsupials, and mammals. Of these, more than 120 species infect snakes, and approximately 50 infect mammals. Hepatozoon canis and Hepatozoon americanum infect wild and domestic canids. Hepatozoon spp. infecting cats include Hepatozoon felis, Hepatozoon silvestris, and organisms closely related or identical to H. canis and H. americanum. • First Described: Hepatozoon canis was first reported in dogs in 1905 in India, and has long been known to infect dogs in many regions of the world, including Asia, Africa, southern Europe, the Middle East, and more recently in North and South America and Australia. The first reports of H. americanum infection were from the Gulf Coast of Texas, United States, in 1978. In 1997, H. americanum was identified as a separate species, distinct from H. canis. Hepatozoon sp. infection in cats was first reported in India in 1908, and infections in felids have since been documented in numerous countries. • Affected Hosts: Hepatozoon canis: domestic dogs, and some wild canids including foxes, jackals, African wild dogs, and coyotes. Hepatozoon americanum: domestic dogs, coyotes, and possibly other mammals. Hepatozoon felis and H. silvestris: domestic and wild felids; other Hepatozoon species infecting cats have also been reported, including H. canis. • Geographic Distribution: Hepatozoon canis is found in canids in numerous countries in all inhabited continents. In the United States, H. canis has been reported in dogs from southern states including Alabama, Georgia, Louisiana, Mississippi, Oklahoma, New Jersey, and Virginia. Hepatozoon americanum infections occur primarily in the south-eastern and south-central United States. Hepatozoon canis and H. americanum co-infections in domestic dogs in North America have been reported in Alabama, Mississippi, and Louisiana. Hepatozoon sp. infections in domestic cats have been reported from many countries including Brazil, France, India, Israel, Nigeria, Portugal, Italy, Thailand, South Africa, Spain, and the United States. • Route of Transmission: Hepatozoon canis is transmitted by ingestion of infected Rhipicephalus sanguineus ticks, and possibly other tick species (Amblyomma ovale, Rhipicephalus turanicus, Rhipicephalus (Boophilus) microplus, Haemaphysalis longicornis, and Haemaphysalis flava). Transplacental transmission of H. canis is also documented. H. americanum is transmitted by ingestion of infected Amblyomma maculatum, and by ingestion of paratenic vertebrate hosts. The route of infection for Hepatozoon spp. infecting cats has not been elucidated, but may involve ingestion of infected arthropod and paratenic host tissues, and possibly transplacental transmission. • Major Clinical Signs: Hepatozoon canis infections in dogs vary greatly in severity from inapparent to severe and life-threatening infections, although dogs are most often subclinically or mildly affected. A compromised immune status tends to lead to more severe disease. In patients with overt disease, clinical signs including fever, anemia, lethargy, and anorexia may be observed. Hepatozoon americanum causes American canine hepatozoonosis (ACH), which is associated with fever, lethargy, bilateral mucopurulent ocular discharge, pain and reluctance to move, altered gait, and muscle atrophy. The majority of cats reported with Hepatozoon sp. are subclinically infected. • Differential Diagnoses: Anemia is the most common hematologic abnormality in dogs with H. canis infection. Therefore, other conditions causing anemia, including other vector-borne diseases, are differentials. For ACH, differential diagnoses include sterile or infectious meningitis, bacterial discospondylitis, Lyme borreliosis, canine monocytic or granulocytic ehrlichiosis, anaplasmosis, toxoplasmosis, sarcocystosis, bacteremia, and systemic immune-mediated diseases such as systemic lupus erythematosus. Cats infected with Hepatozoon spp. should be tested for immunosuppressive diseases including FIV and FeLV infection, and also for hemotropic mycoplasmosis. • Human Health Significance: Canine and feline Hepatozoon species are not known to infect humans.

Original languageAmerican English
Title of host publicationGreene's Infectious Diseases of the Dog and Cat, Fifth Edition
Number of pages18
ISBN (Electronic)9780323509343
ISBN (Print)9780323636209
StatePublished - 1 Jan 2022

Bibliographical note

Publisher Copyright:
© 2021 Elsevier Inc. All rights reserved.


  • Amblyomma
  • Hepatozoon
  • Rhipicephalus
  • gamont
  • myositis
  • vector-borne disease


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