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''Trypanosoma brucei (gambiense)'' is a species of salivary trypanosome which causes African trypanosomiasis, known also as sleeping sickness in humans and nagana in animals. ''T. brucei'' has traditionally been grouped into three subspecies: ''T. b. brucei'', ''T. b. gambiense'' and ''T. b. rhodesiense''. Only rarely can the subspecies ''T.b.brucei'' infect a human. Transmission of ''T. brucei'' between mammal hosts is usually by an insect vector, the tsetse fly. ''T. brucei'' 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 variant surface glycoprotein (VSG) coats, which undergo remarkable antigenic variation, enabling persistent evasion of host adaptive immunity and chronic infection. ''T. brucei'' is one of only a few pathogens that can cross the blood brain barrier. There is an urgent need for the development of new drug therapies, as current treatments 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. ==Infection: Trypanosomiasis== (詳細はtsetse fly (genus ''Glossina''). The initial site of infection is the midgut of the fly (procyclic life cycle stage) and as the infection progresses it migrates via the proventriculus to the salivary glands where it attaches to the salivary gland surface (linked with a differentiation into the epimastigote life cycle stage). In the salivary glands some parasites detach and undergo adaptations (differentiation into the metacyclic life cycle stage) in preparation for injection to the mammalian host with the fly saliva on biting. In the mammal host the parasite lives within the bloodstream (slender bloodstream life cycle stage). Some parasites undergo adaptations (differentiation into the stumpy bloodstream life cycle stage) where it can reinfect the fly vector as it takes a blood meal after biting. In later stages of a ''T. brucei'' infection of a mammalian host the parasite may migrate from the bloodstream to also infect the lymph and cerebrospinal fluids. In addition to the major form of transmission via the tsetse fly ''T. brucei'' may be transferred between mammals via bodily fluid exchange, such as by blood transfusion or sexual contact, although this is thought to be rare.〔(【引用サイトリンク】url=http://www.cdc.gov/parasites/sleepingsickness/epi.html )〕 There are three different subspecies of ''T. brucei'', which cause different variants of trypanosomiasis. *''T. brucei gambiense'' — Causes slow onset chronic trypanosomiasis in humans. Most common in central and western Africa, where humans are thought to be the primary reservoir. *''T. brucei rhodesiense'' — Causes fast onset acute trypanosomiasis in humans. Most common in southern and eastern Africa, where game animals and livestock are thought to be the primary reservoir.〔 *''T. brucei brucei'' — Causes animal African trypanosomiasis, along with several other species of trypanosoma. ''T. b. brucei'' is not human infective due to its susceptibility to lysis by Trypanosome Lytic Factor-1 (TLF-1). However, as it is closely related to, and shares fundamental features with the human infective subspecies, ''T. b. brucei'' is used as a model for human infections in laboratory and animal studies. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trypanosoma brucei」の詳細全文を読む スポンサード リンク
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