Page 455 - Review of Medical Microbiology and Immunology ( PDFDrive )
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PART VI Parasitology
444
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FIGURE 52–11
Trypanosoma brucei. Life cycle. Right side of figure describes the stages within the human (blue arrows). Humans are
infected at step 1 when the tsetse fly bites human and injects trypomastigotes into bloodstream. Tsetse fly is infected at step 5 when it ingests
trypomastigotes in human blood. Left side of figure describes the stages within the tsetse fly (red arrows). (Source: Dr. Alexander J. da Silva and Melanie
Moser, Centers for Disease Control and Prevention.)
are rarely found as amastigotes in tissue, in contrast to
T. cruzi and Leishmania species, in which amastigotes are
The trypomastigotes spread from the skin through the
commonly found.
These trypanosomes exhibit remarkable antigenic vari-
nolence (sleeping sickness) progresses to coma as a result
ation of their surface glycoproteins, with hundreds of anti-
of a demyelinating encephalitis.
genic types found. One antigenic type will coat the surface blood to the lymph nodes and the brain. The typical som-
In the acute form, a cyclical fever spike (approximately
of the parasites for approximately 10 days, followed by
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every 2 weeks) occurs that is related to antigenic variation.
other types in sequence in the new progeny. This variation
As antibody-mediated agglutination and lysis of the trypo-
is due to sequential movement of the glycoprotein genes to
a preferential location on the chromosome, where only that
specific gene is transcribed into mRNA. These antigenic
genic variants survive, multiply, and cause a new fever
variations allow the organism to continually evade the host
spike. This cycle repeats itself over a long period. The lytic
immune response.
antibody is directed against the surface glycoprotein.
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