Comparison of tissue stages of Hepatozoon americanum in the dog using immunohistochemical and routine histologic methods

American canine hepatozoonosis is caused by Hepatozoon americanum, a recent ly described species of apicomplexan protozoan parasite. An immunohistochem ical procedure using a polyclonal antibody to sporozoites of H. americanum clearly identified asexual stages of H. americanum in canine striated muscl e. The method also detects hepatozoa present in naturally infected coyotes and raccoons and reacts with certain other apicomplexans. Use of this immun ohistochemical procedure confirms the canine intermediate host-parasite rel ationships that were presumptively established using conventional histopath ologic methods.