American Canine Hepatozoonosis

American canine hepatozoonosis (ACH) is an emerging disease of dogs in the south-central and southeastern United States. It is a highly debilitating, tick-borne malady that is spread not by the bite of ticks but by dogs ingesting infected ticks. 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. American canine hepatozoonosis (ACH) is caused by Hepatozoon americanum, a protozoal parasite.

Transmission of ACH occurs via ingestion of infected Amblyomma maculatum, the Gulf Coast tick. Dogs are infected by ingesting ticks that contain sporulated oocysts, 5,6 but not by infected ticks taking a blood meal from a dog. Dogs may be infected by ingesting ticks during grooming behavior or eating prey that has attached ticks. When a dog ingests the tick, the sporozoites (very small mobile spores) are released. It is suspected that a sporozoite invades a leukocyte host cell and is transported via the blood to skeletal or cardiac muscle.

Signs The most common clinical signs are fever which ranges from 102.7 to 105.6°F, weight loss, muscle atrophy, 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. Dogs with ACH may display waxing and waning signs of disease, which may eventually result in a chronic wasting condition. Evidence suggests that dogs may become re-infected.

Diagnosis Diagnosis is based on blood tests, clinical signs (eye discharge, fever, etc.), biopsy of tissues (skeletal muscles) and and demonstration of parasites in cysts or granulomas.

Treatment The currently recommended therapy for hepatozoonosis is to administer trimethoprim-sulfadiazine, clindamycin, and pyrimethamine (TCP) for two weeks to destroy protozoa. This regimen is followed by decoquinate, an effective anticoccidial drug, for years. Hepatozoonosis is a life-long infection in dogs. No known treatment completely clears the body of the organism. Remission can be achieved by using drug combination.

Dogs with ACH may experience intense pain and become reluctant to move. 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. It is likely that some dogs with ACH that is never diagnosed recover as a result of good care by owners.

Follow-up therapy with daily administration of decoquinate for two years is recommended to prevent asexual reproduction of the parasite which may lead to an exacerbation of clinical signs of disease. 2 Decoquinate is a coccidiostat that prevents sporozoite development.12

Prevention

It must be said, however, that infected dogs probably represent a minimal risk to other dogs because immature A. maculatum ticks do not favor dogs as hosts.

References
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, Israel
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

Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.