This is another protozoan disease transmitted by the brown dog tick. Of the two types of brown dog ticks seen in the United States, H. americanum causes a more severe illness than H. canis. The geographic distribution of the disease in the United States is limited to Oklahoma, Louisiana, and the Texas Gulf Coast.
In this case, your dog must ingest the tick—perhaps when trying to remove it—to become infected. Illness is most likely to occur in immunosuppressed dogs and pups younger than four months of age. Signs of illness include diarrhea (often bloody), muscle and bone pain with reluctance to move, eye and nasal discharges, and severe loss of weight and body condition.
Treatment: The disease can be treated with a variety of antiprotozoan medications, but a cure has not been established. Most dogs relapse despite treatment, and most die within two years of diagnosis.
Prevention: Hepatozoonosis is best prevented by controlling ticks, as described in Ticks.