American Canine Hepatozoonosis

American canine hepatozoonosis (ACH) is a tick-borne, life-long infection with the protozoan parasite Hepatozoon americanum. It is a highly debilitating illness. When first discovered in the Gulf Coast region in the late 1970s, it was mistakenly thought to be an Old World canine disorder caused by Hepatozoon canis. In the 1990s, veterinarians and veterinary medical researchers came to realize that the New World malady was decidedly more pathogenic than classical canine hepatozoonosis caused by H. canis. No known treatment completely clears the body of the organism, and evidence suggests that dogs may become re-infected.

Transmission of the infection occurs via ingestion of infected Amblyomma maculatum (the Gulf Coast tick). Dogs are infected by ingesting infected ticks during grooming behavior or eating prey that has attached ticks. After the ingestion, sporozoites are released from the tick and invade host leukocytes (white blood cells) that are transported via the blood to skeletal or cardiac muscles. Dogs with ACH may display waxing and waning signs of disease, which may eventually result in a chronic wasting condition. The most common clinical signs are fever ranging from 102.7 to 105.6°F, weight loss, muscle wasting, pus-filled eye discharge, and pain when touched. Many owners report that infected dogs have a generalized stiff gait and hindlimb paralysis. Dogs may eat readily when food is placed immediately in front of them, but they often refuse to move to food and water, presumably owing to intense pain, which derives in part from bone pain and inflamed muscles. Therefore, efforts must be made to ensure that affected animals remain hydrated and that food is readily accessible. Supportive care is important. Pain control has been achieved with nonsteroidal anti-inflammatory drugs.

Diagnosis is based on blood tests, clinical signs, biopsy of skeletal muscles and demonstration of parasites in cysts or granulomas. The current therapy for hepatozoonosis includes trimethoprim, sulfadiazine, clindamycin, and pyrimethamine (TCP) drugs for two weeks to destroy the parasites. This regimen is followed by decoquinate, an effective anticoccidial drug. Follow-up therapy with daily administration of decoquinate for two years is recommended to prevent asexual reproduction of the parasite.

Gulf Coast Tick
Gulf Coast Tick
Amblyomma maculatum
Photo by Laura Johnston

Comparison of the effectiveness of common veterinary tick control products Vectra, Advantix and Frontline based on recent laboratory studies.


  1. American Canine Hepatozoonosis S. A. Ewing* and R. J. Panciera. Department of Pathobiology, College of Veterinary Medicine, Oklahoma State University
  2. Canine Hepatozoonosis--Two Different Diseases Gad Baneth, DVM, PhD, DECVCP School of Veterinary Medicine, Hebrew University Rehovot
  3. American Canine Hepatozoonosis, An Overview Deborah S. Ludlow, DVM; Susan Little, DVM, PhD; Kenneth S. Latimer, DVM, PhD; Bruce E. LeRoy, DVM, PhD; Heather L. Tarpley, DVM

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