Giardia lamblia Life Cycle and Transmission

Study Notes

Giardia Lamblia

Also known as Giardia intestinalis, it is a flagellated parasitic microorganism that colonizes and reproduces in the small intestine, causing a diarrheal condition known as giardiasis.

Habitat and Transmission

Definitive host: Humans (lives in the duodenum and upper part of the jejunum)
Intermediate host: None
Cysts are found in the colon of humans and contaminated materials
Transmission occurs through ingestion of contaminated food and water (fecal-oral route)

Pathogenesis

Infective agent: Mature cyst
Infective dose: About 100 cysts
Trophozoites attach to the bowel wall, causing irritation, low-grade inflammation, and damage to epithelial cells, leading to acute or chronic diarrhea

Epidemiology

Found worldwide, with approximately 50% of stool specimens in the US containing Giardia cysts
Half of those infected are asymptomatic carriers who continue to excrete cysts for years
IgA deficiency predisposes to symptomatic infection
Outbreaks occur related to contaminated water supplies
Hikers who drink untreated stream water are frequently infected
Many species of humans and mammals act as reservoirs
High incidence among children in daycare and patients in mental hospitals

Clinical Findings

Diarrhea (non-bloody and foul-smelling)
Steatorrhea due to malabsorption of fats
Malaise
Weakness
Anorexia
Weight loss
Abdominal cramps and flatulence
Distension due to gas
Nausea and vomiting
Chronic cholecystopathy (when the parasite colonizes the biliary tract)

Diagnostic Laboratory Tests

Microscopy (stool, duodenal aspirate, and serum)
Enzyme-Linked Immunosorbent Assay Test (ELIZA) to detect Giardia antigen in the stool
String Test (if other tests are negative and symptoms persist)

Immunity

Acquired immunity develops in giardiasis
Immunocompromised individuals are more susceptible to massive infection with severe clinical manifestations

Treatment

Tinidazole (tindamax)
Metronidazole (flagyl)
Quinacrine hydrochloride
Furazolidone

Prevention and Control

Avoiding fecal contamination of food and water
Good personal hygiene
Proper sanitation
Purification of municipal water supplies
Avoid using "night soil" (human feces) as a fertilizer
Eating properly cooked food
Chlorination does not kill the cyst, but filtration removes them
Drinking boiled, filtered, or iodine-treated water in endemic areas
No prophylactic drug or vaccine is available

Cryptosporidium

A genus of apicomplexan parasites that causes cryptosporidiosis, characterized by diarrhea
Cryptosporidium hominis is the primary species that causes disease in humans
Cryptosporidium parvum is the former name, no longer used

Morphology

Oocysts: oval-shaped, 5×7um, with a smooth surface and a cleft that allows for sporozoites to be released during excystation
Sporozoites: rough surface, pointed apical region, rounded posterior end, 5×0.5um
Trophozoites: smooth surface, hood-like shape, 1-2.5um in length
Type I and Type II meronts vary in size, with an epicellular, smooth surface and merozoites produced by them are relatively similar in size
Type I merozoites: rod-like shape, pointed apical region, rough surface
Type II merozoites: round, rough surface
Microgametes: spherical, rough surface
Macrogametes: ovular, rough surface

Life Cycle

Oocysts release sporozoites, which form trophozoites
Several stages ensue, involving the formation of schizonts and merozoites
Eventually, microgametes and macrogametes form

Description

Test your knowledge of Giardia lamblia, a parasitic protozoan that infects the human small intestine. Learn about its habitat, transmission, and pathogenesis. Understand how trophozoites multiply and form colonies in the duodenum and upper part of the jejunum.

Giardia lamblia Life Cycle and Transmission

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Questions and Answers

What is the primary method of diagnosing giardiasis in formed stools?

What is the purpose of the String Test in diagnosing giardiasis?

What is the significance of acquired immunity in giardiasis?

What is the most severe symptom of cryptosporidiosis?

What is the purpose of chlorination, filtration, and iodine treatment in preventing cryptosporidiosis?

What is the characteristic shape of the oocyst of Cryptosporidium?

What is the characteristic shape of the sporozoite of Cryptosporidium?

What is the characteristic shape of the trophozoite of Cryptosporidium?

What is the significance of Type I and Type II meronts in the life cycle of Cryptosporidium?

What is the final stage of the life cycle of Cryptosporidium?