This is another protozoan disease transmitted by the brown dog tick, Rhipicephalus sanguineus. Of the two types of brown dog ticks seen in the United States, H. americanum causes a more severe illness than Hepatozoon canis. The geographic distribution of the disease in the United States is limited to Oklahoma, Louisiana, and the Texas Gulf Coast. H canis and H americanum infections occur when an infected tick, the definitive host, is ingested by the dog (or other vertebrate intermediate host). Dogs can also acquire ACH by eating paratenic (transport) hosts that contain cystozoites, a resting stage of H. americanum encysted in their tissues. Illness is most likely to occur in immunosuppressed dogs and pups younger than four months of age in most areas of the world. And in North America clinical signs appear with any other factor i.e. immunosuppression.

Signs of illness:

Signs of illness include diarrhea (often bloody), fever, muscle atrophy and bone pain, stiffness, eye & nasal discharges,  severe loss of weight and weak body condition.


Hepatozoonosis is a lifelong infection in dogs. No known therapeutic regimen completely clears the body of the organism.  But a variety of antiprotozoan medications can be tried. Most dogs relapse despite treatment, and most die within two years of diagnosis. Recommended treatment is trimethoprim-sulfadiazine (15 mg/kg, PO, bid), clindamycin (10 mg/kg, PO, tid), and pyrimethamine (0.25 mg/kg, PO, sid); these drugs should be administered for 14 days.


Hepatozoonosis is best prevented by controlling ticks & discourage predation. Predation presents a dual risk for acquiring ACH: prey captured/ingested by dogs could have infected ticks on their coats that would provide a source of sporozoites; additionally, the prey could contain cystozoites (at least in the case of H. americanum) that are also infectious.