Giardiasis

Giardiasis is an infection of the small intestine caused by Giardia duodenalis (also known as Giardia lamblia or Giardia intestinalis). It is a common diarrheal illness worldwide, particularly where sanitation is poor, and among travelers, daycare attendees, and people who drink untreated water.

Transmission occurs by the fecal-oral route. Ingested cysts from contaminated water, food, or hands survive in the environment and initiate infection. Person-to-person transmission also occurs, especially in households and institutions.

Pathophysiology: In the small intestine, cysts convert to trophozoites that attach to the mucosa, causing malabsorption and inflammation. This can result in diarrhea, steatorrhea, bloating, foul gas, and abdominal pain.

Clinical features: Many infections are asymptomatic. When present, symptoms include diarrhea (which may be intermittent), abdominal cramps, bloating, flatulence, nausea, and weight loss. In children, growth and nutritional issues may occur.

Diagnosis: Stool tests for Giardia antigens or nucleic acid amplification are commonly used. Microscopy can detect cysts or trophozoites but has limited sensitivity; testing multiple stools improves detection. Rarely, duodenal aspirates are used.

Treatment: Antiprotozoal drugs such as metronidazole, tinidazole, or nitazoxanide are commonly used; paromomycin is an alternative. Treatment cures most people within days; relapse or recurrent symptoms can occur in some cases and may require retreatment.

Prevention: Safe drinking water, proper sanitation, hand hygiene, and thorough food preparation reduce risk. Outbreak control focuses on water treatment and identifying and treating cases; in travelers, avoid untreated water and unpasteurized products.

Epidemiology and prognosis: Giardia is one of the most common intestinal parasites worldwide. Most infections resolve with treatment; chronic infection can occur in immunocompromised individuals, and persistent symptoms may require a longer course of therapy.