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• Intestinal flagellates

  • All inhabit the large intestine, except Giardia lamblia (small intestine), Trichomonas vaginalis (urogenital), Trichomonas tenax (mouth)
  • All undergo encystation, except Trichomonas species and Dientamoeba fragilis
  • All are commensals except Giardia lamblia, Dientamoeba fragilis, Trichomonas vaginalis
  • Flagella is attached to the blepharoplast found on the body of the parasite
  • All undergo asexual reproduction through binary fission
• Intestinal flagellates life cycle

  1. Ingestion of cyst

  2. Released in the small intestine

  3. Excystation takes place

  4. Reproduction takes place in the small intestine

  5. Reproduce through binary fission (longitudinal)

  6. Parasite passed in the stool

  7. Either cyst or trophozoite
• Giardia lamblia

  • First discovered in 1859 by French scientist Dr. F. Lambl
  • Also known as G. duodenalis and G. intestinalis
  • Most common cause of intestinal infection worldwide
  • The only protozoan parasite found in the lumen of the human small intestine
  • Man acquires infection by ingestion of cysts in contaminated water and food
  • Habitat: small intestine (duodenum, jejunum, and upper ileum)
  • Low infective dose (only need to ingest around 8-10 cysts to be infected, reason for outbreaks of diarrhea)
  • Beavers: reservoir hosts
  • Reproduce by binary fission, longitudinal
  • Prefers alkaline pH (7.8-8.2), the more alkaline, the more it attaches
• Giardia lamblia trophozoite

  • Pear/pyriform shape, old man's face with eyeglasses
  • 2 nuclei (ovoidal)
  • Axostyle for support
  • 1 pair anterior flagella, 2 pairs lateral flagella, 1 pair conal/posterior flagella
  • 2 Ventral sucking discs (virulence factor)
  • Median/parabasal bodies (2) - energy structures
  • Axoneme (multiple axostyles)
  • Deeply stained curved fibrils
• Giardia lamblia cyst

  • 4 nuclei
  • Refractile/clear cyst wall (hyaline), oval shaped
• Giardia lamblia motility

  • Trophozoite: "Falling Leaf Motility"
  • Cyst: Nonmotile
• Giardia intestinalis may be found worldwide—in lakes, streams, and other water sources—and are considered to be one of the most common intestinal parasites, especially among children
• Ingestion of water contaminated with G. intestinalis is considered to be the major cause of parasitic diarrheal outbreaks in the United States
• G. intestinalis cysts are resistant to the routine chlorination procedures carried out at most water plant facilities
• Filtration as well as chemical treatment of this water is crucial to obtain adequate drinking water
• G. intestinalis may be transmitted by eating contaminated fruits or vegetables
• Person-to-person contact through oral-anal sexual practices or via the fecal-oral route may also transfer G. intestinalis
• Giardiasis (Traveler's Diarrhea)

  Symptomatic infections with Giardia may be characterized by a wide variety of clinical symptoms, ranging from mild diarrhea, abdominal cramps, anorexia, and flatulence to tenderness of the epigastric region, steatorrhea, and malabsorption syndrome
• Patients suffering from a severe case of giardiasis produce light-colored stools with a high fat content that may be caused by secretions produced by the irritated mucosal lining
• The typical incubation period for G. intestinalis is 10 to 36 days, after which symptomatic patients suddenly develop watery, foul-smelling diarrhea, steatorrhea, flatulence, and abdominal cramping
• Giardia lamblia treatment

  The primary choice of treatments are metronidazole (Flagyl), tinidazole (Tindamax) and nitazoxanide (Alinia)
• Giardia lamblia prevention and control

  1. Proper water treatment that includes a combination of chemical therapy and filtration

  2. Guarding water supplies against contamination by potential reservoir hosts

  3. Exercising good personal hygiene

  4. Proper cleaning and cooking of food

  5. Avoidance of unprotected oral-anal sex
• Giardia lamblia laboratory diagnosis

  • Usual specimens: stool/feces
  • Collect 3 specimens in the span of 10 days
  • DFS (to find trophozoites and cyst)
  • Concentration techniques (FECT)
  • Stained smears (permanent)
  • Entero-test/ String Test
  • Duodenal aspirate
  • Serology
  • Molecular methods
  • Biopsy
• Dientamoeba fragilis

  • Initially classified as an amoeba; now an ameboflagellate based on electron microscope study; without external flagella
  • It is seen worldwide and is reported to be the most common intestinal protozoan parasite in Canada
  • NO CYST STAGE
  • The D. fragilis trophozoite is characterized as having one nucleus or two nuclei (binucleate trophozoite more common)
  • The nuclear chromatin usually is fragmented into three to five granules, and normally no peripheral chromatin is seen on the nuclear membrane
  • The cytoplasm is usually vacuolated and may contain ingested debris and some large, uniform granules
  • Stain of choice for distinguishing the individual chromatin granules in the nuclei is iron hematoxylin
• Dientamoeba fragilis habitat and transmission

  • Habitat: colon/large intestine
  • Mode of transmission: oral fecal (ingestion of trophozoites)
  • Relative of Trichomonas
  • Usually ingested with Enterobius and Ascaris - acts as carriers of D. fragilis
  • Reproduction through binary fission
  • High prevalence in developed countries with high sanitation standards (Israel, Holland, Germany, etc.)
  • Hakansson phenomenon: when mounted in water preparations, D. fragilis returns to normal size after swelling unlike the other amebic trophozoites; diagnostic for its identification
• Dientamoeba fragilis life cycle

  1. Ingestion of trophozoites

  2. Goes to the large intestine

  3. Reproduction takes place

  4. Replicates by binary fission

  5. Trophozoites will be located in the lumen of the colon

  6. Parasite passed in the stool

  7. Only trophozoite

  8. Transmission can occur via helminth eggs (Ascaris and Enterobius)
• Dientamoeba fragilis trophozoite

  • 2 nucleus (hence Dientamoeba)
  • Karyosome: Rosette/rose-like
  • Sometimes not detected/seen - fragile, easily destroyed
• The exact mode of D. fragilis transmission remains unknown
• A notable frequency of organisms resembling D. fragilis were identified in patients who were also infected with E. vermicularis (pinworm)
• Data collected and studied to date indicated that this organism is most likely distributed in cosmopolitan areas
• Dientamoeba fragilis clinical symptoms

  • Asymptomatic Carrier State: Most people with D. fragilis infection remain asymptomatic
  • Symptomatic: Patients often present with diarrhea and abdominal pain. Other symptoms may include bloody or mucoid stools, flatulence, nausea or vomiting, weight loss, and fatigue or weakness. Some patients experience diarrhea alternating with constipation, low-grade eosinophilia, and pruritus
• Dientamoeba fragilis treatment

  The treatment of choice is iodoquinol. Tetracycline is an acceptable alternative treatment. Paromomycin (Humatin) may be used in cases when the other treatments are not appropriate
• Because so little is known about the life cycle of D. fragilis, especially the transmission phase, designing adequate prevention and control measures is difficult
• Dientamoeba fragilis prevention and control

  1. Maintaining personal and public sanitary conditions

  2. Avoidance of unprotected homosexual practices

  3. If the unproven transmission theory is valid, the primary prevention and control measure would be the eradication of the helminth eggs, especially those of the pinworm
• Chilomastix mesnili

  • Commensal parasite of the colon/large intestine (cecal region)
  • Infective stage: cyst (ingestion)
  • Excystation happens in the small intestine, trophozoites then go to the large intestine
  • Worldwide distribution
  • No treatment indicated
  • Prevention and control measures: improved sanitation and personal hygiene
• Dientamoeba fragilis

  Asymptomatic Carrier State
• Treatment of Dientamoeba fragilis infections

  1. Treatment of choice is iodoquinol

  2. Tetracycline is an acceptable alternative

  3. Paromomycin (Humatin) may be used when other treatments are not appropriate
• Dientamoeba fragilis

  • It is estimated that most people with D. fragilis infection remain asymptomatic
  • Patients who suffer symptoms often present with diarrhea and abdominal pain
  • Other documented symptoms may include bloody or mucoid stools, flatulence, nausea or vomiting, weight loss, and fatigue or weakness
  • Some patients experience diarrhea alternating with constipation, low-grade eosinophilia, and pruritus
• Prevention and Control of Dientamoeba fragilis

  • Maintaining personal and public sanitary conditions and avoidance of unprotected homosexual practices will help minimize the spread
  • If the unproven transmission theory is valid, the primary prevention and control measure would be the eradication of the helminth eggs, especially those of the pinworm
• Chilomastix mesnili

  Commensal parasite of the colon/large intestine (cecal region)
• Chilomastix mesnili


  • Infective stage: cyst (ingestion)
  • Excystation happens in the small intestine
  • Trophozoites then go to the large intestine
• Chilomastix mesnili has worldwide distribution
• No treatment is indicated for Chilomastix mesnili infections
• Prevention and control of Chilomastix mesnili


  Improved sanitation and personal hygiene
• Life cycle of Chilomastix mesnili

  1. Ingestion of cysts

  2. Parasite goes to the colon/large intestine and develops and reproduces

  3. Parasite is passed in the feces

  4. Cysts usually contaminates food, water, hands of people, and other fomites