Cilia and Flagellates

• Balantidium coli


  Causes balantidiasis, balantidiosis, or balantidial dysentery
• Trophozoite


  • Cilia arranged in longitudinal pattern extending from oral to caudal region
  • Cytostome (oral apparatus at tapered end)
  • Cytopyge (rounded posterior end)

  
• Trophozoite


  • Two dissimilar nuclei
  • Macronucleus: bean-shaped, easily identified in stained specimens
  • Micronucleus: round, lies in the concavity of the macronucleus

  
• Cyst


  • Spherical to slightly ovoid
  • Thick cell walls (double-walled)
  • Encystation does not result in increase number of nuclei
  • Infective stage
• Mode of transmission


  Ingestion of food and/or water contaminated with cyst
• Habitat


  Large intestine of man, pigs and monkeys
• Natural host, accidental host, reservoirs

  • Natural host: Pig
  • Accidental host: Man
  • Reservoirs: Pig, monkeys, and Rat
• Life cycle


  1. Ingestion → excystation (small intestine) → trophozoites colonize large intestine (reside in lumen of large intestine and appendix of humans and animals where they replicate by binary fission, during which conjugation may occur

  2. Trophozoites undergo encystation to produce infective cysts

  3. Some trophozoites invade colon wall and multiply → ulcerative pathology

  
• Pathogenesis and clinical manifestations

  • Characteristic ulcer with a rounded base (vs. flask-shaped, narrow necked ulcers of amebiasis)
  • Cause of ulceration: HYALURONIDASE
• Intrinsic host factors that contribute to host susceptibility and severity

  • Nutritional status
  • Intestinal bacteria flora
  • Achlorhydria
  • Alcoholism
  • Presence of chronic disease
• Forms of Balantidiasis


  • Asymptomatic carriers
  • Fulminant balantidiasis/ Balantidial dysentery
  • Chronic form
• Pathogenesis and clinical manifestations

  • Can spread to extraintestinal sites: Mesenteric nodes, Appendix, Liver, Genitourinary sites, Pleura and lungs
  • Complications: Intestinal perforation, Acute appendicitis
• Diagnosis

  1. Microscopic demonstration of trophozoites and cysts in feces using direct examination or concentration (sedimentation or flotation) techniques

  2. Repeated stool examinations may be done to increase sensitivity

  3. Demonstration of presence of trophozoites in biopsy specimens from lesions obtained through sigmoidoscopy

  4. Bronchoalveolar washings in case of pulmonary infection
• Culture


  Locke's egg albumin medium, NIH polyxenic medium
• Giardia duodenalis


  Also known as Giardia intestinalis or Giardia lamblia, causes giardiasis
• Trophozoite


  • Pyriform/ teardrop shaped, pointed posteriorly
  • Pair of ovoidal nuclei, one on each side of the midline
  • Dorsal side: CONVEX
  • Ventral side: CONCAVE with large adhesive disc for attachment
  • Bilaterally symmetrical
  • Axostyle: distinct medial line
  • Two sausage-shaped parabasal/ median bodies
  • Propelled into an erratic tumbling motion by four pairs of flagella arising from superficial organelles in ventral side of the body
• Antigenic variation results in the entire surface of the parasite being covered with variant-specific surface proteins (VSPs)
• Cyst


  • 2 nuclei: young cysts
  • 4 nuclei: mature cysts
  • Flagella retracted into axonemes (median or parabasal body) and deeply stained curved fibrils surrounded by a tough hyaline cysts wall secreted from condensed cytoplasm
• Mode of transmission


  Ingested of mature cysts from contaminated hands, food or water
• Life cycle

  1. In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites)

  2. Typically seen within crypts of duodenal and jejunal mucosa. It does not invade the tissue, but remains tightly adhered to intestinal epithelium by means of the sucking disk

  3. Encystation occurs as the parasites transit toward the colon.

  
• Pathogenesis and clinical manifestations

  • Alter mucosal intestinal cells once it has attached to apical portion of enterocyte
  • Attaches to intestinal cells via an adhesive sucking disc located on the ventral side → mechanical irritation in the affected tissues
  • Lectin, when activated by duodenal secretions → facilitate attachment
  • Once attached, able to avoid peristalsis by trapping itself in between the villi or within the intestinal mucus
  • Villous flattening and crypt hypertrophy → decreased electrolyte, glucose, and fluid absorption → deficiencies in disaccharidases → malabsorption and maldigestion
  • Alteration in cytoskeleton in human colonic and duodenal monolayers → cytoskeleton disruption (enterocyte apoptosis)
  • Excessive flatus with an odor of "rotten eggs" due to hydrogen sulfide
  • Diarrhea most common symptom
  • Chronic infection → steatorrhea (passage of greasy, frothy stools)
• Diagnosis


  1. Demonstration of trophozoites and/or cysts in stool specimens

  2. Floating- leaf-like motility in DFS

  3. Concentration techniques for cysts

  4. At least three stool examinations on alternate days are recommended because of spotty shedding of cysts

  5. Duodeno-jejunal aspiration

  6. Enterotest: Swallows a gelatin capsule attached to a nylon string attached to patient's cheek, after ~4-6 hours, string removed and any adherent fluid is placed on the slide for microscopic examination

  7. Antigen detection tests

  8. Immunofluorescent tests
• Trichomonas vaginalis


  Causes trichomoniasis
• Trophozoite


  • Exists only in the trophozoite stage
  • Pyriform shape
  • Four free anterior flagella that appear to rise from a simple stalk
  • Fifth flagellum embedded in the undulating membrane (extends about half of organism's length
  • Median axostyle
  • Single nucleus

  
• Habitat


  • Female: vagina, may ascend as far as the pelvis
  • Men: urethra, prostate, less frequently in epididymis
• Pathogenesis and clinical manifestations

  • Cannot live without close association with the vaginal, urethral or prostatic tissues
  • Degeneration and desquamation of the vaginal epithelium followed by leukocytic inflammation of tissue layer
  • Acute inflammation → liquid vaginal secretions, greenish or yellow in color (cover the mucosa down to the urethral orifice, vestibular glands, and clitoris)
  • Intense itchiness, burning sensation
  • Speculum examination: Hemorrhages of the cervix "strawberry cervix"
• Diagnosis


  1. Quickest and most inexpensive way to diagnose trichomonads: saline preparation of vaginal fluid

  2. Gold standard: Culture (takes 2 to 5 days) - Diamond's modified medium, Feinberg and Whittington culture medium

  3. Unstained wed drop preparations: fixed and stained by Giemsa, Papanicolau, Romanowsky, Acridine orange stains

  4. Papsmear (60% sensitivity; 95% specificity)

  5. Antigen detection tests

  6. PCR
• Trichomonas hominis


  Non-pathogenic flagellate
• Trichomonas hominis


  • Exists only as trophozoite
  • Pyriform shape
  • Five anterior flagella and posterior flagellum projecting from an undulating membrane
  • Cytostome, nucleus – anterior end
  • Axostyle extends from anterior to posterior along the mid-axis

  
• Mode of transmission


  Fecal contamination of food and drinks
• Habitat


  Cecal area of the large intestines of humans and other primates
• Trichomonas tenax


  Harmless commensal of the human mouth
• Trichomonas tenax


  • Trophozoite stage only
  • Smaller and slender than Trichomonas vaginalis
  • Four free equal flagella; fifth flagellum on the margin of an undulating membrane which does not reach the posterior end, and lacks a free posterior extension
• Mode of transmission


  Droplet spray from the mouth, kissing or common use of contaminated dishes and drinking glasses
• Chilomastix mesnili


  Inhabits cecal region
• Chilomastix mesnili trophozoite


  • Asymmetrically pear-shaped
  • Result of spiral groove extending through the middle half of the body
  • Boring and spiral forward movement
  • Three anterior free flagella and a more delicate one within the prominent cytostome
• Chilomastix mesnili cyst


  • Pear- or- lemon-shaped
  • Single large vestibular nucleus
  • Cytostome (almost as long as the encysted organism)
• Diagnosis


  Demonstration of either cysts or trophozoites