Hepatozoon spp

From Dog
Gamont of Hepatozoon canis in neutrophils from peripheral blood smear[1]
Generalized hyphema with corneal edema[2]

Hepatozoon spp are a hemotropic tick-borne Apicomplexan protozoan parasite of dogs in all continents with tropical and subtropical climates[3][4].

These protozoa are usually transmitted by Rhipicephalus spp and Haemaphysalis spp ticks[5].

Species which are pathogenic to dogs include:

  • Hepatozoon canis
  • Hepatozoon americanum[6]

All Hepatozoon species have the same life cycle: gametogony and sporogony in the definitive host (a bloodsucking invertebrate) and schizogony followed by formation of gametes in the intermediate host (a vertebrate). The definitive host of Hepatozoon canis is the brown dog tick Rhipicephalus sanguineus, and the intermediate hosts are dogs and wild canids.

Hepatozoon canis infects leukocytes and parenchymal tissues and is transmitted to dogs by the ingestion of ticks containing mature oocysts[7]. Following ingestion of infected ticks, sporozoites spread via the bloodstream and lymph to several organs including the spleen, bone marrow, lung, liver and kidney. In these organs, meronts are formed and undergo several cycles of merogony, releasing merozoites, which invade white bloods cells (mostly neutrophils and monocytes) where they form gamonts[8].

Co-infections with other hemoplasmas such as Babesia spp, Echrlichia canis and Leishmania infantumis are common[9][10].

Clinically affected dogs usually present with anemia and neutropenia. H. canis may also induce severe clinical manifestations such as fever, anorexia, weight loss and lymphadenopathy associated with a high parasite load. Skin lesions have also been reported associated with localized infections[11], as well as anterior uveitis, glaucoma, osteomyelitis, protozoal polyradiculoneuritis and hypertrophic osteoarthropathy following systemic infection[12].

A presumptive diagnosis is based on exposure to ticks and presenting clinical signs and a definitive diagnosis requires cytological examination of blood or buffy coat smears, indirect fluorescent antibody test (IFA)[13] or PRC assays[14].

Treatment of hepatozoonosis is with imidocarb dipropionate whereas H. americanum infection is treated with an initial combination of trimethoprim-sulfadiazine, pyrimethamine and clindamycin followed by maintenance with decoquinate[15].

However, failures have been reported with imidocarb, even when used in combintation with toltrazuril.

Treatment for both diseases has not been reported to facilitate complete parasite elimination and new effective drugs are needed for the management of these infections[16].

Tick control is an essential preventative method with dogs[17].


  1. Pasa, S et al (2009) Description of dogs naturally infected with Hepatozoon canis in the Aegean region of Turkey. Turk J Vet Anim Sci 33(4):289-295
  2. Acevedo T et al (2009) Uveitis and glaucoma associated with Hepatozoon canis infection: a case report. Rev Colom Cienc Pecua 22:287-295
  3. Vargas-Hernandez G et al (2012) Molecular characterization of Hepatozoon canis in dogs from Colombia. Parasitol Res 110(1):489-492
  4. O'Dwyer LH et al(2011) Brazilian canine hepatozoonosis. Rev Bras Parasitol Vet 20(3):181-193
  5. Qablan MA et al (2012) Stray dogs of northern Jordan as reservoirs of ticks and tick-borne hemopathogens. Parasitol Res 111(1):301-307
  6. Allen KE et al (2011) Hepatozoon spp infections in the United States. Vet Clin North Am Small Anim Pract 41(6):1221-1238
  7. Baneth G et al (2001) Transmission of Hepatozoon canis to dogs by naturally-fed or percutaneously-injected Rhipicephalus sanguineus ticks. J Parasitol 87:606–611
  8. Baneth G et al (2007) Life cycle of Hepatozoon canis (Apicomplexa: Adeleorina: hepatozoidae) in the tick Rhipicephalus sanguineus and domestic dog (Canis familiaris). J Parasitol 93:283–299
  9. Spolidorio MG et al (2011) Molecular detection of Hepatozoon canis and Babesia canis vogeli in domestic dogs from Cuiabá, Brazil. Rev Bras Parasitol Vet 20(3):253-255
  10. Otranto D et al (2010) Prevention of endemic canine vector-borne diseases using imidacloprid 10% and permethrin 50% in young dogs: A longitudinal field study. Vet Parasitol 172:323–332
  11. Little L & Baneth G (2011) Cutaneous Hepatozoon canis infection in a dog from New Jersey. J Vet Diagn Invest 23(3):585-588
  12. Shimokawa Miyama T et al (2011) Neutropenia associated with osteomyelitis due to Hepatozoon canis infection in a dog. J Vet Med Sci 73(10):1389-1393
  13. Shkap V et al (1994) Circulating antibodies to Hepatozoon canis demonstrated by immunofluorescence. J Vet Diagn Invest 6:121–123
  14. Otranto D et al (2011) Diagnosis of Hepatozoon canis in young dogs by cytology and PCR. Parasit Vectors 4:55
  15. Baneth G (2011) Perspectives on canine and feline hepatozoonosis. Vet Parasitol 181(1):3-11
  16. Pasa S et al (2011) Failure of combination therapy with imidocarb dipropionate and toltrazuril to clear Hepatozoon canis infection in dogs. Parasitol Res 109(3):919-926
  17. Dantas-Torres F et al (2011) Hepatozoon canis infection in ticks during spring and summer in Italy. Parasitol Res 110(2):695-698