CHAPTER TWO2.0 DESCRIPTION OVERVIEW, LIFE CYCLE OF TRYPANOSOMA2.1. Cellular structure of the trypanosome Trypanosomes are unicellular protozoa having a single flagellum that contains microtubules in the 9+2 arrangement typical of other flagella. At the base of the flagellum is the kinetoplast which contains DNA in the form of approximately 6000 connected circles. Kinetoplast DNA constitutes 10% of total cellular DNA where the action of some anti-trypanosome drugs such as ethidium occurs. The kinetoplast is part of the single long mitochondrion that undergoes structural changes during various stages of the life cycle. The surface of the trypanosome formed by the bloodstream contains a dense layer of variable surface glycoproteins (VSGs) which is replaced by an equally dense layer of procyclins when the parasite segregates into the procylic form in the midgut of the tsetse fly. tse (Ogbadoyi et al., 2000). Trypanosoma brucie, a flagellated protozoan, is the causative parasite of the infectious disease known as African trypanosomiasis (African sleep disease) in Africa, while in America Trypanosoma cruzi causes Chagas disease which is prevalent in humans and animals, both of which are fatal if untreated (Brun et al., 2010; Carlier et al., 2003; Pereira et al., 2011). African trypanosomiasis is the leading cause of death in 36 sub-Saharan African countries with approximately 70,000 deaths per year. year (Barrett et al., 2003; Keith, 2005). There are two subspecies of Trypanosoma brucei that cause sleeping sickness in humans: Trypanosoma brucei gambiense, Trypanosoma brucei rhodesiense while African animal trypanosomiasis or nagana disease is caused by T. congolense, T. vivax and Trypanosoma brucei brucei. Trypanosoma brucei brucei is non-infectious for... middle of paper ......va immune response) that occurs in the trypanosoma. Thus, persistent infection in the host results in continuity of the trypanosome replication cycle, development of the immune complex, and change in the surface coat glycoprotein ( Taylor and Authie, 2004 ; Sinshaw et al., 2006 ). The clinical signs of AAT are intermittent fever, signs of anemia, lymphadenopathy, anemia, anorexia, dullness, inactivation, depression, loss of milk and meat production and death in untreated cases, and weight loss. In the pathogenesis of trypanosomiasis, immunosuppression is the most important and complicating factor caused by trypanosomes to their host. It is difficult to conclude which clinical signs are due to a given parasite and only a few studies have been conducted in this aspect to identify a specific sign for particular trypanosomes (Murray and Dexter, 1988; Garner et al., 2003).