Trypanosoma brucei is a species of parasitic protozoan belonging to the genus Trypanosoma. It causes African trypanosomiasis, known also as sleeping sickness in humans and nagana in other animals. T. brucei has traditionally been grouped into three subspecies: T. b. brucei, T. b. gambiense and T. b. rhodesiense. The latter two are typically parasites of humans, while the first is that of other animals. Only rarely can the T.b.brucei infect a human.
- bruceiis transmitted between mammal hosts by aninsect vector belonging to the species of tsetse fly. 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 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.
Reproduction
Binary fission
The reproduction of T. brucei is unusual compared to most eukaryotes. The nuclear membrane remains intact and the chromosomes do not condense during mitosis. The basal body, unlike the centrosome of most eukaryotic cells, does not play a role in the organisation of the spindle and instead is involved in division of the kinetoplast. The events of reproduction are:
- The basal body duplicates and both remain associated with the kinetoplast. Each basal body forms a separate flagellum.
- Kinetoplast DNA undergoes synthesis then the kinetoplast divides coupled with separation of the two basal bodies.
- Nuclear DNA undergoes synthesis while a new flagellum extends from the younger, more posterior, basal body.
- The nucleus undergoes mitosis.
- Cytokinesisprogresses from the anterior to posterior.
- Division completes with abscission
Meiosis
In the 1980s, DNA analyses of the developmental staged of T. brucei started to indicate the trypomastigote in tsetse fly undergo meiosis, i.e. sexual reproduction stage. But it is not always necessary for a complete life cycle. The existence of meiosis-specific proteins was reported in 2011. The haploid gametes (daughter cells produced after meiosis) were discovered in 2014. The haploid trypomastigote-like gametes can interact with each other via their flagella and undergo cell fusion (the process called syngamy).Thus, in addition to binary fission, T. brucei can multiply by sexual reproduction. Trypanosomes belong to the supergroup Excavata and are one of the earliest diverging lineages among eukaryotes. The discovery of sexual reporduction in T. brucei supports the hypothesis that meiosis and sexual reproduction are ancestral and ubiquitous features of eukaryotes.
Susceptibility against human serum
Trypanosoma brucei brucei (as well as related species T. equiperdum and T. evansi) is not human infective because it is susceptible to innate immune system ‘trypanolytic’ factors present in the serum of some primates, including humans. These trypanolytic factors have been identified as two serum complexes designated trypanolytic factors (TLF-1 and -2) both of which contain haptoglobin related protein (HPR) and apolipoprotein LI (ApoL1). TLF-1 is a member of the high density lipoprotein family of particles while TLF-2 is a related high molecular weight serum protein binding complex. The protein components of TLF-1 are haptoglobin related protein (HPR), apolipoprotein L-1 (apoL-1) and apolipoprotein A-1 (apoA-1). These three proteins are colocalized within spherical particles containing phospholipids and cholesterol. The protein components of TLF-2 include IgM and apolipoprotein A-I.
written by. Shahmshad Ahmed Khan
