Trypanosoma gambiense

Trypanosoma brucei is a species of parasitic kinetoplastid belonging to the genus Trypanosoma. The parasite is the cause of a vector-borne disease of vertebrate animals, including humans, carried by genera of tsetse fly in sub-Saharan Africa. In humans T. brucei causes African trypanosomiasis, or sleeping sickness. In animals it causes animal trypanosomiasis, also called nagana in cattle and horses. T. brucei has traditionally been grouped into three subspecies: T. b. brucei, T. b. gambiense and T. b. rhodesiense. The first is a parasite of non-human vertebrates, while the latter two are the known parasites of humans. Only rarely can the T. b. brucei infect a human. T. brucei is transmitted between mammal hosts by an insect vector belonging to different species of tsetse fly (Glossina). Transmission occurs by biting during the insect's blood meal. The parasites undergo complex morphological changes as they move between insect and mammal over the course of their life cycle. The mammalian bloodstream forms are notable for their cell surface proteins, variant surface glycoproteins, which undergo remarkable antigenic variation, enabling persistent evasion of host adaptive immunity leading to chronic infection. T. brucei is one of only a few pathogens known to cross the blood brain barrier. There is an urgent need for the development of new drug therapies, as current treatments can have severe side effects and can prove fatal to the patient. Whilst not historically regarded as T. brucei subspecies due to their different means of transmission, clinical presentation, and loss of kinetoplast DNA, genetic analyses reveal that T. equiperdum and T. evansi are evolved from parasites very similar to T. b. brucei, and are thought to be members of the brucei clade. The parasite was discovered in 1894 by Sir David Bruce, after whom the scientific name was given in 1899. T. brucei comprises a species complex that includes: T. brucei is a typical unicellular eukaryotic cell, and measures 8 to 50 μm in length. It has an elongated body having a streamlined and tapered shape. Its cell membrane (called pellicle) encloses the cell organelles, including the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and ribosomes. In addition, there is an unusual organelle called the kinetoplast, which is made up of numerous circular DNA (mitochondrial DNA) and functions as a single large mitochondrion. The kinetoplast lies near the basal body with which it is indistinguishable under microscope. From the basal body arises a single flagellum that run towards the anterior end. Along the body surface, the flagellum is attached to the cell membrane forming an undulating membrane. Only the tip of the flagellum is free at the anterior end. The cell surface of the bloodstream form features a dense coat of variant surface glycoproteins (VSGs) which is replaced by an equally dense coat of procyclins when the parasite differentiates into the procylic in the tsetse fly midgut. Trypanosomatids show several different classes of cellular organisation of which two are adopted by Trypanosoma brucei at different stages of the life cycle: These names are derived from the Greek mastig- meaning whip, referring to the trypanosome's whip-like flagellum. The trypanosome flagellum has two main structures. It is made up of a typical flagellar axoneme, which lies parallel to the paraflagellar rod, a lattice structure of proteins unique to the kinetoplastida, euglenoids and dinoflagellates.