A. Giardia lamblia & Balantidium coli
Giardia lamblia
Disease: Giardiasis
Morphology
- Trophozoite: Pear-shaped, binucleate (two identical nuclei with central karyosomes), four pairs of flagella, ventral sucking disc, axonemes, parabasal bodies, two blepharoplasts
- Cyst: 7–10 μm, oval, thick-walled, four nuclei
Hosts: Humans, mammals (cats, dogs), birds
Life Cycle
- Cysts survive weeks in cold water and harsh conditions
- Infection by ingestion of cysts via contaminated water, food, or fecal-oral route
- Excystation in small intestine → trophozoites emerge
- Trophozoites attach to intestinal mucosa and multiply by binary fission in proximal bowel
- Encystation occurs during transit to colon
- Cysts (mainly) and rarely trophozoites passed in feces
- Only cysts survive outside host
Transmission
- Contaminated water, food, poor hygiene (fecal-oral)
Symptoms
- Diarrhea, steatorrhea, epigastric pain
- Malaise, excessive gas, vomiting
Diagnosis
- Confined to lumen of small intestine
- Detection of cysts or Giardia antigen in stool (multiple samples may be needed)
Prevention
- Boil untreated water
- Avoid using stream/river water for food or brushing
- Hand hygiene, safe food practices, peel fruits and vegetables
Balantidium coli
Disease: Balantidiasis (balantidial dysentery)
Morphology
- Largest intestinal protozoan
- Trophozoite: ~60 μm, sac-shaped, covered with cilia, cytostome, gullet, macronucleus & micronucleus, food & contractile vacuoles
- Cyst: 52–55 μm, thick-walled, contains macronucleus; viable for weeks
Hosts: Humans and pigs
Life Cycle
- Similar to Entamoeba histolytica
- Cysts are infective; no multiplication in cyst stage
- After ingestion, cyst wall dissolves → trophozoites invade intestinal wall and multiply
Symptoms & Pathology
- Destruction of mucosa and submucosa
- Acute: 6–15 stools/day with blood, mucus, pus
- Chronic: diarrhea, constipation, anemia, cachexia
- Many cases asymptomatic
Diagnosis
- Identification of trophozoites in diarrheic stool
- Cysts in formed stool
- Multiple stool exams recommended
- Sigmoidoscopy in rectosigmoid disease