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Erlandsen S. Knodler L. Silberman J. Davids B. Elmendorf H. Singer S. Nucleic Acids Res. Okada M. Akimaru H. Hou D. Takahashi T. Parasites - Giardia. Section Navigation. Facebook Twitter LinkedIn Syndicate. Pathogen and Environment. Minus Related Pages. Causal Agent Giardia duodenalis is a protozoan flagellate Diplomonadida. Life Cycle Giardia cysts can contaminate food, water, and surfaces, and they can cause giardiasis when swallowed in this infective stage of their life cycle.
Minus Related Pages. Read CDC's new report describing giardiasis outbreaks during Read the Report. General Information. Illness and Symptoms. Prevent Illness. Acute infection develops over a period of three weeks, peaking at eight days post infection. Generally, healthy hosts clear the infection within 2—3 weeks, whereas the occasional chronically infected host shows signs of villus and crypt atrophy, enterocyte apoptosis, and ultimately severe disruption of epithelial barrier function [ 5 ].
Infection with G. To date, four types of endomembrane compartments have been identified in the Giardia trophozoite, namely: the endoplasmic reticulum ER , the nuclei, terminally-differentiated mitochondrial remnants named mitosomes, and peripheral vacuoles PVs [ 7 ]. Encystation-specific vesicles ESVs constitute a fifth compartment present only in encysting cells.
Extreme genomic divergence has led to frequent artefacts such as long-branch attraction in earlier phylogenetic studies [ 8 ]. Combined with observations of elements of prokaryotic metabolism and the absence of bona fide eukaryotic organelles such as the Golgi apparatus, endosomes, and mitochondria, this resulted in a misclassification of G. However, molecular paleontology approaches aimed at identifying machinery present in the last eukaryotic common ancestor LECA indicated that this organism likely possessed all extant eukaryotic organelles and corresponding trafficking pathways.
This supports the notion that species with a simplified cellular organization such as the ancestor of G. Interestingly, recent efforts aimed at rooting the eukaryotic tree place this root between the Excavata supergroup, to which G.
Due to streamlining of most anabolic pathways, G. This active host—pathogen interface is at the crossroads of both endo- and exocytic trafficking in G. The main function of PVs is to periodically endocytose fluid-phase extracellular material and to expel harmful or unusable substances into the environment again.
This is in contrast to the unidirectional endocytic uptake of fluid-phase material via cytostome-like structures in many protozoa as well as in Spironucleus spp. The flushing of the PV lumen makes exchange of fluid-phase material bidirectional and likely compensates for the lack of bona fide lysosomes as endpoints of endocytic transport. Endocytosis through PVs is likely the main route of nutrient uptake into the Giardia cell, although there are isolated reports on receptor-mediated uptake of lipid particles.
Short actin filaments were also shown to be involved in LDL uptake and were localized in close proximity to PVs [ 14 ]. Released cargo travels further to the lumen of connecting ER tubules. Some cargoes green pentagon can be excluded from further passage to the ER.
Completion of the life cycle by transmission of G.
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