Trypanosoma brucei
Gabriela Romero-Meza1
and Monica R. Mugnier1,
*
1
Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
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Trypanosoma brucei causes African trypanosomiasis in humans and nagana in domestic animals. This vectorborne
parasite, transmitted by the tsetse fly, affects rural areas in sub-Saharan Africa. When injected by the fly,
metacyclic-form parasites are introduced into the host dermis and then disseminate into the bloodstream as replicative
long slender forms. Throughout its life cycle, T. brucei is entirely extracellular. To evade host antibody recognition,
the parasite uses antigenic variation: it periodically changes a dense coat of only one kind of variant
surface glycoprotein (VSG), drawing from a genomic repertoire of about 2000 VSG-encoding genes. Using quorum
sensing mechanisms, slender forms develop into stumpy forms that are preadapted to the insect environment.
Once taken up by the fly, the parasite replaces its VSG coat with procyclins and progresses through procyclic
and epimastigote stages. Finally, the parasites become VSG-expressing metacyclic trypomastigotes.
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KEY FACTS:
T. brucei possesses a unique organelle,
the kinetoplast: a network of circular
DNA inside a single mitochondrion.
The 35 Mb diploid genome contains
three types of chromosome: megabase,
intermediate, and minichromosomes.
The 11 megabase chromosomes contain
the majority of transcriptionally active genes
arranged in polycistronic units, as well as
subtelomeric arrays of silent VSG genes.
Minichromosomes and intermediate
chromosomes contain VSG genes and
DNA repeats.
T. brucei typically invades tissues, including
blood, lymph, bone marrow,
skin, brain, eye, and heart.
DISEASE FACTS:
T. brucei is lysed by a primate serum
component called trypanosome lytic
factor (TLF), rendering it noninfectious to
humans. Trypanosoma brucei
gambiense and Trypanosoma brucei
rhodesiense are resistant to TLF and can
infect humans.
Symptoms in the early stage of infection:
fever, joint pain, and swollen lymph
nodes. In the late stage the central nervous
system is affected.
Detection of parasites in body fluids by
microscopy is required for diagnosis.
After treatment, patients are monitored
for relapse by a periodic check for parasites
and leukocyte counts in the cerebrospinal
fluid.
Affected populations live in areas with
limited access to diagnosis and treatment,
but human African trypanosomiasis
is on its way to elimination in most
endemic countries.
TAXONOMY AND CLASSIFICATION:
PHYLUM: Euglenozoa
CLASS: Kinetoplastida
ORDER: Kinetoplastida
FAMILY: Trypanosomatidae
GENUS: Trypanosoma
SPECIES: T. brucei
*Correspondence:
mmugnie1@jhu.edu (M.R. Mugnier).
Trends in Parasitology, June 2020, 36, No. 6 © 2019 Elsevier Ltd. All rights reserved. https://doi.org/10.1016/j.pt.2019.10.007 571
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Acknowledgments
M.R.M. is supported by the Office of the Director, National Institutes of Health (DP5OD023065). VSG figure adapted from Engstler, 2007. We thank Jay Bangs, School of Medicine,
University at Buffalo, and Peter Bush, School of Dental Medicine, University at Buffalo, for the T. brucei scanning electron microscope (SEM) image.
Resources
www.cdc.gov/parasites/sleepingsickness/
www.who.int/trypanosomiasis_african/parasite/en/
https://tritrypdb.org/tritrypdb/
Literature
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