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Pathogenesis: Giardia

Giardia is an extracellular intestinal parasite with a life cycle that includes cysts and trophozoites, where cysts are infective and trophozoites are not. Infection leads to symptoms such as malabsorption, diarrhea, and bloating, and can be treated with metronidazole or tinidazole. Giardia is resistant to chlorine treatment, posing a risk in contaminated water supplies.

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12 views1 page

Pathogenesis: Giardia

Giardia is an extracellular intestinal parasite with a life cycle that includes cysts and trophozoites, where cysts are infective and trophozoites are not. Infection leads to symptoms such as malabsorption, diarrhea, and bloating, and can be treated with metronidazole or tinidazole. Giardia is resistant to chlorine treatment, posing a risk in contaminated water supplies.

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fanvksheyqkqlwhvxm
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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152 7 Foodborne Parasites

in sewage affluent. Wild animals, such as b­ eavers, and contain two nuclei and four flagella, and they
can carry the protozoa and contaminate water. display tumbling motility (Fig. 7.2). Trophozoites
use surface protein, alpha-giardins to attach to
Pathogenesis the intestinal epithelium for colonization and
Giardia is an extracellular parasite and resides in infection. They multiply rapidly through asexual
the intestinal lumen. Giardia life cycle has two reproduction and cause damage to the mucus
stages: cyst and trophozoite. Cysts are infective membrane and disrupt epithelial tight junction
while trophozoites are not. The infective dose is barrier to increase intestinal permeability in the
10–100 cysts, and the incubation period is upper small intestine. During chronic infection,
1–2 weeks. Once ingested, the cyst (ovoid, giardia downregulates tight junction protein,
9–12 μm long) arrives in the duodenum and is claudin 1, and increases epithelial apoptosis.
dissolved by digestive enzymes, and two tropho- Some trophozoites mature into the cyst, before
zoites (9–21 μm long and 5–15 μm wide) are being released into the feces completing its life
released. The trophozoites are teardrop shaped cycle. Giardiasis is characterized by malabsorp-
tion, severe watery diarrhea, bloating, and flatu-
Table 7.1 Foodborne parasites lence. Treatment with metronidazole or tinidazole
Group Genus/species can eliminate the infection. Giardia is resistant to
Protozoa Giardia lamblia; Entamoeba chlorine treatment that is applied to municipal
histolytica water supplies.
Cyclospora; Cryptosporidium;
Cystoisospora
Toxoplasma gondii; Trypanosoma cruzi
Cestodes Taenia saginata; T. solium Entamoeba histolytica
(tapeworms) Echinococcus granulosus
Nematode Ascaris lumbricoides Introduction
(roundworms) Trichinella spiralis The genus Entamoeba consists of several spe-
Trematodes Clonorchis sinensis cies: Entamoeba histolytica, E. dispar, E. mosh-
(flatworms or Paragonimus spp kovski, E. coli, E. hartmanni, and E. polecki.
flukes) Fasciola hepatica Entamoeba histolytica is pathogenic and the

Fig. 7.1 General life


cycle of parasites

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