Giardiasis

A 24 year old male presents with 2 weeks of foul-smelling diarrhea associated with abdominal bloating, excessive flatulence, and mild weight loss. Symptoms began shortly after returning from a hiking trip where he drank untreated stream water. He reports greasy, foul-smelling stools that float and worsen after dairy intake. He denies fever or blood in stool. Physical examination is unremarkable except for mild abdominal distension. Stool studies are negative for inflammatory cells. Diagnosis?

Diagnosis is Giardiasis.

1. Definition

Giardiasis is a protozoal infection of the small intestine caused by Giardia duodenalis (formerly Giardia lamblia) resulting in functional mucosal disruption and malabsorption, leading to diarrhea and gastrointestinal symptoms.

2. Etiology

1. Caused by Giardia duodenalis
2. Transmission:
• Fecal–oral route
• Contaminated water
• Contaminated food
• Person-to-person spread
3. Risk factors:
• Camping or hiking
• Drinking untreated water
• International travel
• Childcare exposure
• Male-male sexual contact
• Immunodeficiency (especially IgA deficiency)

3. Pathophysiology

1. Ingestion of infectious cysts
2. Gastric acid triggers excystation in the small intestine → release of trophozoites
3. Trophozoites attach to the proximal small intestinal mucosa via a ventral adhesive disc
4. This results in:
• Functional disruption of absorption
• Brush-border enzyme deficiency
• Mild villous blunting
• Malabsorption
5. Giardia generally causes functional impairment rather than direct invasive tissue destruction
6. Secondary consequences:
• Fat malabsorption
• Secondary lactose intolerance
• Weight loss

4. Clinical Features

4.1 Core Features

1. Foul-smelling diarrhea
2. Bloating
3. Flatulence
4. Abdominal cramps
5. Weight loss
6. Greasy or floating stools (steatorrhea)

4.2 Associated Features

1. Exposure history:
• Travel
• Camping
• Untreated freshwater exposure
2. Stool characteristics:
• Greasy stools
• Usually non-bloody
3. Other features:
• Malabsorption
• Lactose intolerance
• Vitamin deficiencies (chronic disease)
4. Less common:
• Fever
• Vomiting

5. Diagnosis

1. Stool antigen test (commonly used)
2. Multiplex PCR
• Highest sensitivity where available
3. Direct fluorescent antibody (DFA) test
• Very sensitive
4. Stool ova and parasite microscopy:
• Detection of cysts or trophozoites
• Three stool samples improve diagnostic yield

6. Management

6.1 Supportive Treatment

1. Oral rehydration
2. Electrolyte replacement

6.2 Antimicrobial Therapy

1. Tinidazole: Preferred single-dose therapy
2. Metronidazole: Commonly used alternative
3. Nitazoxanide: Alternative option
4. Pregnancy:
• Paromomycin preferred if treatment is necessary

7. Key Clinical Insight

Foul-smelling greasy diarrhea with bloating, flatulence, steatorrhea, weight loss, and recent untreated water exposure strongly suggests Giardiasis

8. Exam Level Pearls

1. Most commonly diagnosed intestinal protozoal infection in the United States
2. Infection may occur after ingestion of as few as 10 cysts
3. Causes malabsorption and secondary lactose intolerance
4. Stool is typically non-bloody
5. First-line treatment commonly includes tinidazole or metronidazole