Microscopic Identification of Common Parasitic Causes of Diarrhea

Giardia lamblia - Morphology, Life Cycle, and Pathogenesis

Giardia lamblia, a protozoan parasite, is one of the leading causes of diarrheal diseases worldwide. Its microscopic identification is crucial for effective diagnosis and treatment.

1. Morphology

Giardia lamblia exists in two forms:

• Trophozoite: The active, feeding form. It has a pear-shaped body, with four pairs of flagella aiding mobility.
• Cyst: The dormant, resistant form that survives in harsh conditions, making transmission possible.

2. Life Cycle

The life cycle consists of the following stages:

1. Ingestion of cysts through contaminated water or food.
2. Excystation in the small intestine, releasing trophozoites.
3. Trophozoites attach to the intestinal mucosa, reproducing asexually.
4. Encystation occurs, with cysts passing into feces, completing the cycle.

3. Pathogenesis

Giardiasis is characterized by:

• Watery diarrhea due to disruption of the intestinal lining.
• Malabsorption of nutrients leading to weight loss.
• Abdominal pain and bloating.
• Prolonged infection in immunocompromised individuals.

4. Diagnosis and Treatment

Diagnosis includes microscopic identification, stool antigen tests, and PCR assays. Treatment involves:

• Metronidazole or Tinidazole as first-line drugs.
• Preventive measures like boiling water and proper hygiene.