MIDTERM: OTHER INTESTINAL PROTOZOANS

Question 1

• causes BLASTOCYSTOSIS
• previously classified as yeast under the genus Schizosaccharomyces
• taxonomists suggested that it was related to Blastomyces
  o due to glistening appearance in a wet mount and the absence of any
  organelle of locomotion
  o capable of pseudopodial extension and retraction
  o responds to anti-protozoal drugs

Answer 1

Blastocystis hominis

Question 2

Morphological forms of B. hominis:
o MOST PREDOMINANT FORMS in fecal specimens
o Shape: spherical
o Size: 5-10um in diameter
o large central vacuole pushes the cytoplasm and the four nuclei to the periphery of the cell
o sometimes, very thick capsule surrounds the vacuolated forms
o Reproductive organelle: prominent central vacuole
o main type of Blastocystis that cause diarrhea

Answer 2

Vacuolated

Question 3

Morphological forms of B. hominis:
o Size: 2.5-8um
o occasionally observed in stool samples
o exhibit active extension and retraction of pseudopodia.
o Visible Nuclear Chromatin: shows peripheral clumping
o INTERMEDIATE STAGE between the vacuolar form and the precystic form
o allows the parasite to ingest bacteria in order to enhance encystment

Answer 3

Ameba-like forms

Question 4

Morphological forms of B. hominis:
o MULTINUCLEATED
o Mainly observed from old cultures
o Size: 10-60um
o Granular contents: develop into daughter cells of the ameba-form when the cell ruptures

Answer 4

Granular forms

Question 5

Morphological forms of B. hominis:
o arise from vacuolated forms
o believed to produce many vacuolated forms.
o RESISTANT CYSTIC FORM: 3 to 10 μm in diameter, has 1 or 2 nuclei
o very prominent and thick, osmophilic, electron dense wall
o appears as a sharply demarcated polymorphic, but mostly oval or circular, dense body surrounded by a loose outer membranous layer.

Answer 5

Multiple Fission

Question 6

o responsible for EXTERNAL TRANSMISSION

Answer 6

B. hominis Thick-walled cyst

Question 7

may be the cause of REINFECTION within a host’s intestinal tract

Answer 7

B. hominis Thin-walled cyst

Question 7

Blastocystis is difficult to eradicate

T OR F?

Answer 7

TRUE
o Hides in intestinal mucus
o Sticks and holds on to intestinal membranes

Question 8

drug of choice

Answer 8

o METRONIDAZOLE given orally, 750 mg
three times daily for 10 days
o (Pediatric dose: 35-50 mg/kg/day in
three doses for 5 days)
o IODOQUINOL given at 650 mg three
times daily for 20 days

Question 9

found to resolve symptoms in 86% of patients after 3 days of administration

Answer 9

Nitazoxanide

Question 10

first discovered Dientamoeba fragilis in 1909

Answer 10

Wenyon

Question 11

o first described in the scientific literature in 1918

Answer 11

Jepps and Dobell

Question 12

• originally described as an ameba
• a flagellate (only the trophozoite stage known)
• NO CYST STAGE
• closely related to and resembles Trichomonas
• Location: lives in the mucosal crypts of the appendix, cecum and the upper colon
• Transmission: Direct human to human transmission is probably via the fecal-oral route or via transmission of helminth eggs particularly that of Enterobius vermicularis
• Dientamoeba-like mononucleated and binucleated forms have been observed in the lumen of Enterobius
• Animal Reservoirs: macaques, gorillas, and swine
• CAPABLE OF CO-INFECTION WITH Enterobius

Answer 12

Dientamoeba fragilis

Question 13

• size: 7 to 12 µm with one or two (rarely three or four) ROSETTE-shaped nuclei
• Nuclear Membrane: no peripheral chromatin
• Karyosome: four to six discrete granules
• Cytoplasm: may contain vacuoles with ingested debris

Answer 13

Dientamoeba fragilis TROPHOZOITE

Question 14

Dientamoeba fragilis DIAGNOSIS:
- provide more suitable material for examination than the average formed stool

Answer 14

Purged stool specimens

Question 15

Dientamoeba fragilis TREATMENT

Answer 15

• Antimicrobial therapy
• iodoquinol at 650 mg three times daily for 20 days
• (pediatric dose is 40 mg/kg/day in three doses, also for 20 days)
• Tetracycline and metronidazole