The carcass was emaciated with gray streaks in the myocardium, an enlarged friable liver with capsular rupture and hemorrhage, hemoperitoneum, and mild splenomegaly. Skeletal muscle was pale with reduced mass. The temporal muscles were especially pale and atrophied. Parasitic forms of H. canis occur in many organs and tissues of the body but are most frequently present in skeletal and cardiac muscle. Inflammatory changes associated with encysted forms of the organism tend to be minimal.
Granulomatous responses appear to occur when excystment and gamont development occur.
Hepatozoon canis is a protozoan in the family Haemogregarinidae, phylum Apicomplexa. Distribution of Hepatozoon canis is worldwide and its life cycle is similar to other Hepatozoon species. The infected nymphal or adult brown dog tick contains the infective parasitic oocyst within its hemocoel. Ingestion of the tick is the only known mode of natural transmission. Sporozoites are released, penetrate the intestinal wall, and are then transported by the blood or lymph to mononuclear phagocytes especially in the spleen and bone marrow but also multiple other tissues.