Protozoa

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Protozoa

• Review slides 22-25
  single-celled wall-less Eukaryotes Protista
• 4 phyla based upon motility
• Sarcodina (amoeba)
• Mastigophora (flagellates)
• Ciliophora (ciliates)
• Sporozoa no organelles of motility
• asexual reproduction for all but Sporozoa
• few protozoa use an intermediate host

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Protozoa

• Intestinal and urogenital protozoa
• pathogens
• commensals / non-pathogens
• Blood and tissue parasites

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Intestinal ameba

• Pathogens Tom vs text Entamoeba
  histolytica Dientamoeba fragilis
  (flagellate without flagella - Tom) Blastocystis
  hominis
• Commensals significant as look-alikes, esp. E.
  histolytica Entamoeba dispar Entamoeba
  coli Entamoeba hartmanii
  Endolimax nana Iodamoeba butschlii

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Focus on pathogens Entamoeba histolytica

• Facts / life-cycle simplest possible life-cycle
  direct fecal-oral transmission through fecal
  contaminated food or water. Cysts ingested
  release 4 trophs in intestine. Common in highly
  populated under-developed areas. Poor hygiene,
  poor infra-structure ingestion of raw or
  undercooked contaminated food or water is the
  problem (same old story). No need for IH or
  environmental maturation. Only cysts can survive
  outside of body.
• Epidemiology 5x107 infections worldwide with
  infection rates 50 in endemic areas such as C.
  S. America, Africa, Asia. Accounts for
  100,000 annual deaths. Hot spots include
  Bangladesh, Brazil, Mexico City, Manilla.
  Infection rates of the U.S. population in some
  areas reach 3. Children are the primary hosts
  of the organism. Why?

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Focus on pathogens E. histolytica
pathology/clinical symptoms

• Note since diagnosis of protozoans strictly by
  morphology is more difficult, symptoms are used
  as more of a clinical tool in protozoan
  infections than in helminth infections.
• 90 of patients are asymptomatic contributing to
  the spread of disease. Long term infection will
  result in pathogenesis. Damage may go unnoticed
  for some period of time. Trophs are responsible
  for all pathology.

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Focus on pathogens E. histolytica
pathology/clinical symptoms cont.

• Intestinal may be a single event or recurrent
• a)amoebic colitis cramps with alternation
  between loose stool and constipation
• b)dysentery seen in 0 of infected patients
  - hydrolytic enzymes penetrate small hole or
  ulcer in mucosa, reaches musculature spreads
  laterally causing significant undercutting
  severe pain, sloughing of mucosa ? blood mucus
  in diarhea, tear drop or flask-like
  intestinal lesions.

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E. histolytica pathology continued

• extraintestinal involves a small fraction (0.5)
  of infections. Trophs perforate bowel causing
  peritonitis, and travel to other organs
• liver crater-shaped abcesses on surface of
  liver with chocolate colored exudat
• anemia, weight loss elevated
  alkaline phosphatase due to liver damage,
• abcesses in brain, lung, kidney even more rare

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Typical pathology of E. histolytica a)
flask-shaped abcess in mucosa b)
crater-shaped liver abcess c) liver abcess
damage tube of chocolate puss from abcess

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Focus on pathogens E. histolytica diagnosis/ID

• Diagnosis can be difficult due to varied clinical
  symptoms and presentations of the organism, as
  well as similarities with the commensal Entamoeba
  species. READ text on pg 1082.
• Molecular methods recently indicated that 80 of
  cases previously thought to be E. histolytica
  were actually infections of commensal species
  such as E. dispar. 500,000 ?100,000
• Cysts are present in formed stools cysts
  trophs in semi-formed stool. Both trophs and
  cysts can be diagnostic in both wet preps and
  permanent stained smears. Demonstration of
  characteristic cysts and trophs in permanently
  stained smears is necessary for accurate
  speciation. Debbie? Is this true?
• Toms slides ?

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Focus on pathogens E. histolytica diagnosis/ID
cont.

• Diagnostic features of trophs in wet preparations
• Directional motility by way of hyaline (glassy,
  transparent) elongated or finger-like pseudopods
• May contain RBCs ingested via phagocytosis
• Nuclear details not visible or definitive
  (requires permanent staining)

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