Giardia

• Giardia lamblia / Giardia duodenalis


  Also known as G. intestinalis
• Epidemiology


  • Worldwide (children and adults)
  • Males > females
  • Associated with outbreaks, usually water-borne
  • Also food-borne
  • US: 4% of 300,000 stool examination
  • Common among the institutionalized areas, such as jails, in developing countries
  • PH: 1.6 – 22% prevalence
  • Common in lower class economy
• Cyst


  • Ovoid shape
  • Mature twice (2 then 4 nuclei)
  • Quadrinucleated cyst – mature cyst, infective stage
  • Nucleus is more visualized in iodine preparation
  • Retracted flagella appear like 4 pairs of curved bristles
  • Axostyle
  • Parabasal body
  • 2 parabasal bodies associated to the retracted flagella
  • Cytoplasm retracted from the cyst wall ("double-walled"), refractile cell wall
  • Cell wall is smooth, refractile, and well defined
  • More prevalent in children > adults
• Trophozoite


  • "old man wearing eyeglasses, tennis racket"
  • 9 – 12 um long x 5 – 15 um wide
  • Tear drop / pear-shaped, bilaterally symmetrical
  • Rounded anteriorly, pointed posteriorly
  • Convex dorsal side
  • Divide by longitudinal binary fission
  • "falling leaf motility" or "tumbling"
  • 2 nuclei
  • Axostyle and parabasal body
  • 4 pairs of flagella
  • Ventral sucking disc for attachment to the intestinal mucosa
• 1 axostyle - Structure that lines throughout the body. Divides the right and left portion of the G. lamblia into two equal parts
• 2 axonemes - Supporting structures / internal flagella
• Parabasal bodies - Contains mitochondrial DNA which supplies energy to the flagella for locomotion
• • Paired nuclei on each side of midline
  • Ovoidal with central karyosomes
  • 4 pairs of flagella reside = falling leaf motility
  • One pair anterior
  • One pair posterior
  • 2 pairs ventral
• Life Cycle of Giardia lamblia

  1. Ingestion of contaminated water, food, or maybe in hands or fomites with infective cyst

  2. The infective stage is the mature or quadrinucleated cyst

  3. The cyst excysts in the small intestine to form the trophozoite

  4. Trophozoite multiplies through longitudinal binary fission

  5. When there is an extreme environment or in formed stools, it will become a cyst by the process of encystation

  
• Methods of Transmission


  • Ingestion of cyst
  • Fecal-oral route (most common mode)
  • Water-borne
  • Food-borne
  • Venereal: Oral-anal contact (sexually transmitted, usually by homosexual individuals)
• Infective stage


  Mature or 4-nucleated cyst
• Habitat


  Duodenum of the small intestine
• Encystation


  • Large intestines (the site for water reabsorption, dehydrating stools – not a suitable environment for trophozoites to thrive, hence they encyst)
  • Trophozoites easily disintegrate in extreme environments such as in formed or hard stool
• Giardia lamblia can be found in the duodenum, jejunum, and upper segment of the ileum
• Giardia lamblia divides by longitudinal binary fission
• Pathogenesis


  1. Human infection begins with the ingestion of mature quadrinucleated cyst

  2. Excystation happens in the duodenum to release trophozoites

  3. G. lamblia inhabits the duodenum, jejunum, and upper ileum

  4. Trophozoites are attached to the mucosal surface by sucker, reproduced by longitudinal binary fission

  5. Sucking disc and lectin help the organism to attach to the intestinal cells which later lead to irritation

  6. Shortening of microvilli, elongation of crypts, and damaging the brush border of the absorptive cells

  7. Trophozoites do not invade intestinal tissues but feed on the mucosecretion

  8. Mechanical blockage of the intestinal mucosa, competition for nutrients, inflammation

  9. Does not invade mucosa and submucosa, only attaches to the microvilli, causing deficiency in sucrase and maltase

  10. Chronic infection – coating of the large intestinal area with mucus because the trophozoite feeds on the mucus produced by enterocyte. This produce a barrier to fat absorption

  
• Symptoms


  • Diarrhea, abdominal pain, excessive flatus with characteristic rotten egg odor, bloating, nausea, vomiting, and steatorrhea
  • Steatorrhea – excess mucous production serves as a barrier for fat absorption
• Pathology


  • Acute infection (Cramping abdominal pain with diarrhea, excessive flatus, abdominal bloating, malaise, nausea, anorexia)
  • Chronic infection (Steatorrhea, periods of diarrhea alternating with constipation)
  • Asymptomatic/ carrier state
• Diagnosis


  • Demonstration of trophozoite and/or cyst in stool
  • Examination of duodenal contents demonstrate the trophozoite
  • Entero-test: patient swallows a gelatin capsule containing a nylon string, one end is attached to patient's cheek; after 6 – 8 hours, string is removed and adherent fluid is examined
  • Antigen detection (immunofluorescent test) - Cyst wall protein 1 – CWP1 antigen
• Treatment


  Metronidazole – attacks and kills trophozoite
• Prevention and Control


  • Sanitary disposal of human excreta
  • Food and water precaution
  • Good hand hygiene