There are two species in domestic animals. H. hammondi in cats and H. heidorni in canines. Both are obligatory two-host parasites with life cycles similar to Toxoplasma. For H. hammondi goats and rats are intermediate hosts while humans and other mammals are intermediate hosts for H. hammondi . The generalized life cycle involves the intermediate hosts becoming infected by eating sporulated oocysts.
Sporozoites excyst and invade intestinal cells, become tachyzoites and multiply.
The parasite eventually encysts in muscles. This tissue-cyst forming coccidian parasite is similar to Sarcocystus . The brain cysts are lobulate and contain septa. Schizonts and gamonts are formed in intestinal cells and the resulting oocysts are shed in the feces. Many believe that the organism may be mechanically transmitted by biting arthropods.