ISSN 2398-2942      

Hepatozoon americanum





  • Phylum: Apicomplexa
  • Class: Sporozoea
  • Subclass: Coccidia
  • Order: Euccidiiae
  • Family: Haemogregarinidae
  • Genus: Hepatozoon

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Clinical Effects



  • The disease has been reported in the geographic habitat of the host tick,Amblyomma maculatum. It is also found in wildlife (coyotes, raccoons, and bobcats) in the same geographical area.


  • The dog ingests the infected tick vector (Amblyomma maculatum) with oocysts. Sporozoites are released into the intestine of the dog. They penetrate the intestinal wall and enter an unidentified host cell. This cell is carried hematogenously to a peripheral site (usually skeletal muscle) where merogony occurs within the host cell Tissue specimen containing a meront.
  • After 21 - 32 days, the host cell ruptures and zoites are released, creating an intense pyogranulomatous reaction Muscle specimen showing a pyogranuloma. Infected neutrophils enter the bloodstream to either be ingested by the tick host or redistributed throughout the dog to form additional meronts. Continued release of zoites with resultant pyogranulomatous myositis causes the chronic waxing and waning fever and other clinical signs.


  • To date, the only form of transmission proven is the ingestion of infectedAmblyomma maculatumticks.
  • Transmission did not occur with Rhipicephalus spp. ticks or with ingestion of infected tissues.

Pathological effects

Other Host Effects

  • H. americanum causes clinical signs of disease in naturally and experimentally infected dogs. Subclinical infections have not been identified in healthy dogs.


Control via chemotherapies

  • For immediate remission of clinical signs (within 48-72 hours), administer the following combination of drugs for 14 days: trimethoprim sulfadiazine Trimethoprim , 15 mg/kg PO q 12 h; clindamycin Clindamycin , 10 mg/kg PO q 8 h; and pyrimethamine Pyrimethamine , 0.25 mg/kg PO q 24 h.
  • For long term control and prevention of relapse, adminster the coccidiostat, decoquinate daily for 18 - 24 months. The dosage is 10 - 20 mg/kg added to food q 12 h (0.5 - 1.0 teaspoon per 10 kg BW Deccox 22.7 g/lb mixture).
  • For palliative control of fever and muscle pain, administer NSAIDs Analgesia: NSAID at standard doses.

Other countermeasures

  • Aggressive tick control is warranted.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Macintire D K, Vincent-Johnson N A, Kane C W et al (2001) Treatment of dogs infected with Hepatozoon americanum: 53 cases (1989-1998). J Am Vet Med Assoc 218 (1), 77-82 PubMed.
  • Mathew J S, Saliki J T, Ewing S A et al (2001) An indirect enzyme-linked immunosorbent assay for diagnosis of American canine hepatozoonosis. J Vet Diagn Invest​ 13 (1), 17-21 PubMed.
  • Panciera R J, Ewing S A, Mathew J S et al (1999) Canine hepatozoonosis: comparison of lesions and parasites in skeletal muscle of dogs experimentally or naturally infected with Hepatozoon americanumVet Parasitol 82 (4), 261-272 PubMed.
  • Mathew J S, Ewing S A, Panciera R J et al (1998) Experimental transmission of Hepatozoon americanum Vincent-Johnson et al., 1997 to dogs by the Gulf Coast tick, Amblyomma maculatum Koch.​ Vet Parasitol 80 (1), 1-14 PubMed.
  • Panciera R J, Ewing S A, Mathew J A et al (1998) Observations on tissue stages of Hepatozoon americanum in 19 naturally infected dogs. Vet Parasitol 78 (4), 265-276 PubMed.
  • Macintire D K, Vincent-Johnson N, Dillon A R et al (1997) Hepatozoonosis in dogs: 22 cases (1989-1994). J Am Vet Med Assoc 210 (7), 916-922 PubMed.
  • Panciera R J, Gatto R T, Crystal M A et al (1997) Canine hepatozoonosis in Oklahoma. J Am Anim Hosp Assoc 33 (3), 221-225 PubMed.
  • Vincent-Johnson N A, Macintire D K, Lindsay D S et al (1997) A new Hepatozoon species from dogs: description of the causative agent of canine hepatozoonosis in North America. J Parasitol 83 (6), 1165-1172 PubMed.
  • Vincent-Johnson N A, Macintire D K, Baneth G (1997) Canine hepatozoonosis: pathophysiology, diagnosis and treatment. Compend Contin Educ Pract Vet 19 (1), 51-65 VetMedResource.
  • Craig T M, Jones L P, Nordgren R M (1984) Diagnosis of Hepatozoon canis by muscle biopsy. J Am Anim Hosp Assoc 20 (2), 301-303 VetMedResource.

Other sources of information

  • Craig T M (1998) Hepatozoonosis. In: Clinical microbiology and infectious diseases of the dog and the cat. Ed C E Greene. Philadelphia. W B Saunders Co. 458-465.

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