Biology Reference
In-Depth Information
the order kinetoplastida, so called because of a DNA-containing organelle within the
mitochondria known as the kinetoplast. In addition to the kinetoplast, these parasites
are characterized by the presence of a single flagellum, an organelle that plays a key
role in several critical cell functions, such as motility, cell division, morphogenesis,
attachment to vector- and host-cell surfaces, immune evasion, and consequently, the
viability and pathogenic potential of the parasite (Hunger-Glaser and Seebeck
1997
;
Broadhead et al.
2006
). The life cycle of the kinetoplastid parasites is complex,
comprising both insect and human stages that involve morphological and metabolic
adaptation of the parasite to enable survival and propagation in the differing envir-
onments encountered (Black and Seed
2001
; Farrell
2002
; Tyler and Miles
2002
).
The life cycle of each parasite is shown in Fig.
1
.
Human Stages
Insect Stages
The insect takes a bloodmeal:
T. brucei
:
Tsetse fly injects metacyclic trypomastigotes
T. cruzi
:
Triatomine bug deposits feces containing metacyclic trypomastigotes at bite site
Leishmania
:
Sandfly injects promastigotes
T. brucei/cruzi:
Epimastigotes transform into
metacyclic trypomastigotes
T. brucei:
Metacyclic trypomastigotes transform
into bloodstream trypomastigotes
Leishmania:
Promastigotes transform into
metacyclic promastigotes
T. cruzi:
Metacyclic trypoamstigotes penetrate
various cells at bite site and transform
into amastigotes
Leishmania
: Promastigotes are phagocytized by
macophages and transform
into amastigotes
T. br ucei/cr uzi:
Procyclic trypomastigotes
transform into epimastigotes
T. brucei:
Trypomastigotes multiply in blood, lymph
and cerebrospinal fluid
T. brucei:
Bloodstream trypomastigotes
transform into procyclic
trypomastigotes
Bloodstream trypomastigotes
transform into epimastigotes
Leishmania:
Amastigotes are released from
macrophages and transform
into promastigotes
T. cruzi:
Amastigotes multiply inside cells,
transform into trypomastigotes and burst
out of cell into bloodstream
T. cruzi:
Leishmania:
Amastigotes multiply, burst out of cell
and infect macrophages
The insect takes a bloodmeal:
T. brucei:
Tsetse fly ingests bloodstream trypomastigotes
*
T.cruzi:
Triatomine bug ingests bloodstream trypomastigotes
Leishmania:
Sandfly ingests macrophages infected with amastigotes
Fig. 1 Life cycles of
T. brucei
,
T. cruzi
, and
Leishmania
. *Bloodstream trypomastigotes exist in
two forms: the long slender proliferating form and the short stumpy nonproliferating form that is
preadapted for survival in the tsetse fly
