These are leaf-like protozoan organisms found in the blood tissues of different vertebrates. They are worldwide in distribution. They are characterized by the presence of a flagellum, an undulating membrane, a kinetoplast, and a blepharoplast. The developmental stages are trypomastigote, epimastigote, promastigote and amastigote. Some species of this family have pathogenic significance causing massive loss in the livestock industry. The gold standard for the diagnosis of this parasitic infection is the examination of blood smears. Control of the parasite mostly relies on chemotherapy.