Case Discussion

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Case Discussion

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Present illness

• A 22-year-old male college student, who had
  recently returned from a surfing trip to
  Acapulco, Mexico, presented to the emergency
  department suffering from crampy abdominal pain,
  malaise, nausea, fever, and bloody, mucoid
  diarrhea. Stool specimens were collected and sent
  to the laboratory for routine culture for
  enteric bacilli and examination for ova and
  parasites.

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• Lab finding
• Stool cultures were negative for bacterial
  pathogens
• A moderate number of ameboid trophozoites,
  measuring 20 to 30 µm, with finely granular
  cytoplasm, evenly distributed peripheral nuclear
  chromatin, and ingested red blood cells were seen
  in the permanent trichrome stain.

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Q1

• Based on the morphological description given,
  which intestinal parasite would you suspect is
  causing this patient's infection? Could this
  parasite be confusedwith nonpathogenic
  parasites? If so, which nonpathogenic parasites
  could it be confused with?
• Ans
• 1. Entamoeba histolytica
• 2. Entamoeba dispar , Entamoeba coli and
  Entamoeba hartmanni

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• Acute amebic colitis has a gradual onset
  presenting with a 1- to 2-week history of
  abdominal pain, diarrhea, and tenesmus. Stool
  samples, which are watery and contain blood and
  mucus, have little fecal material. Fever is noted
  in only a minority of patients. Lower quadrant
  abdominal tenderness may be noted.
• The trophozoite of E histolytica averages 25 µm,
  ranging from 10-60 mm. It has a clear ectoplasm
  and a somewhat granular endoplasm containing
  several vacuoles. The trophozoite has a single 3-
  to 5- µm nucleus with fine peripheral chromatin
  and a central nucleolus. Ingested RBCs may be
  present within the trophozoite.

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• Other Problems to be Considered
• Infectious
• Shigella
• Salmonella
• Enteroinvasive Escherichia coli
• Enterohemorrhagic Escherichia coli
• Noninfectious
• Inflammatory bowel disease
• ischemic colitis
• Diverticulitis

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??Entamoeba histolytica??Salmonella ?
Shigella
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Q2

• Although no information regarding the stool
  consistency (formed, semisolid, or liquid) was
  given, what would you suspect the consistency of
  this patient's stool to be? Why?
• Ans liquid
• Formed ? ??stool???cyst
• semisolid ???stool???cyst ?trophozoite
• liquid ???stool???trophozoite

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Q3

• Which nonpathogenic parasite is morphologically
  indistinguishable from this parasite? What
  characteristic can be used to differentiate
  pathogenic from nonpathogenic species of this
  parasite?
• Ans
• 1. Entamoeba dispar is a nonpathogenic protozoon
  morphologically identical to E histolytica. These
  2 species of Entameba can be distinguished by the
  monoclonal antibodies.
• 2. Other morphologically distinct organisms, such
  as Entamoeba coli and Entamoeba hartmanni, are
  also nonpathogenic

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• Entamoeba hartmanni trophozoites (4-12 µm) are
  similar to E.histolytica trophozoites, present a
  small karyosome often eccentrical.
• Entamoeba coli trophozoites measure 20-30 µm and
  have a vescicolous nucleus with a large eccentric
  karyosome and an irregulary distributed
  peripheral chromatin. The cytoplasm is vacuolated
  containing bacteria and yeast.

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Q4

• Is this parasite capable of causing
  extraintestinal infection? Explain.
• Ans
• Extraintestinal disease
• Liver abscess
• Pleuropulmonary disease
• Peritonitis
• Pericarditis
• Brain abscess
• Genitourinary disease

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Q5

• How is this parasite transmitted?
• Ans
• ? Humans are the only reservoir of E histolytica.
  Cysts passed in the feces can survive in moist
  environmental conditions for weeks to months.
  Upon ingestion of fecally contaminated food or
  water, the cysts travel to the small intestine,
  where the trophozoites are released. In 90 of
  patients, the trophozoites re-encyst and produce
  asymptomatic infection, which usually resolves
  spontaneously within 12 months. In the
  remaining10 of patients who are infected, the
  parasite causes symptomatic amebiasis. Under
  unfavorable conditions, the trophozoite reverts
  to the cyst form, and the life cycle is repeated.

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Q6

• What laboratory techniques are recommended to
  diagnose infection with this parasite?
• Ans
• Enzyme immunoassay (EIA) This is the best test
  for making the specific diagnosis of E
  histolytica in the clinical setting
• Indirect hemagglutination antibody (IHA) test
  detects antibody specific for E histolytica.
• Immunodiffusion (ID) is simple to perform, making
  it ideal for the laboratory that has only an
  occasional request for amebic serology
• immunoglobulin M (IgM) antibodies specific for E
  histolytica has been reported,

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Q7

• Should this patient be treated? How?
• Ans
• Asymptomatic intestinal infection may be treated
  with iodoquinol, paromomycin, or diloxanide
  furoate.
• drugs for treatment of symptomatic intestinal
  disease and for hepatic abscess are metronidazole
  and tinidazole.
• Surgical intervention may be necessary in
• ?Patients with severe colitis requiring
  intravenous volume replacement
• ?Patients with fulminant colitis that may require
  surgical intervention
• ?Patients with liver abscess of uncertain
  etiology or not responding to therapy
• ?Patients with suspected liver abscess rupture

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Q8

• Discuss the pathogenesis of amebiasis.
• Ans

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• Invasive disease begins with the adherence of E
  histolytica to colonic mucins, epithelial cells,
  and leukocytes. Adherence of the trophozoite is
  mediated by a galactose-inhibitable adherence
  lectin.
• After adherence, the trophozoites of E
  histolytica lyse the target cells by using lectin
  to bind to the target cells' membranes and using
  the parasite's ionophorelike protein to induce a
  leak of ions (ie, Na, K, Ca) from the target
  cell cytoplasm.
• A number of hemolysins, encoded by plasmid
  (ribosomal deoxyribonucleic acid rDNA) and
  cytotoxic to the intestinal mucosal cells.
• An extracellular cysteine kinase causes
  proteolytic destruction of the tissue, producing
  flask-shaped ulcers

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Q9

• Describe the life cycle of this parasite.
• Ans
• ? Humans are the only reservoir of E histolytica.
  Cysts passed in the feces can survive in moist
  environmental conditions for weeks to months.
  Upon ingestion of fecally contaminated food or
  water, the cysts travel to the small intestine,
  where the trophozoites are released. In 90 of
  patients, the trophozoites re-encyst and produce
  asymptomatic infection, which usually resolves
  spontaneously within 12 months. In the
  remaining10 of patients who are infected, the
  parasite causes symptomatic amebiasis. Under
  unfavorable conditions, the trophozoite reverts
  to the cyst form, and the life cycle is repeated

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Q10

• Discuss the epidemiology of this infection.
• Ans
• ?Approximately 10 of the world's population is
  infected by either E histolytica or E dispar.
  Amebiasis affects about 50 million persons each
  year, resulting in approximately 100,000 deaths,
  all of which are due to E histolytica. Incidence
  of amebiasis is higher in developing countries.
  Areas of high prevalence include the Indian
  subcontinent, southern and western Africa, the
  Far East, South America, and Central America

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Q11

• Discuss the prevention and control of amebiasis.
• Ans
• ?Educate patients about the prevention of
  amebiasis during travel to endemic areas. This
  includes avoiding drinking contaminated water and
  avoiding eating raw fruits and salads, which are
  difficult to sterilize. Bottled water may be used
  during such travel. Eating only cooked food or
  self-peeled fruits in endemic areas minimizes risk

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Referance

• 1. Chen KT, Malison MDOutbreak of Scombroid fish
  poisoning, in Taiwan. Am J pub Hlth
  1987771335-1336.
• 2. Lai SC, Chu YJ, Kno CF, et al A survey of
  hyperuricemia in Tungau and Tungyueh of Ilam
  County. Department of Health Executive Yuan ROC.
  Epidemiology Bulletin 19917 99-105.
• 3. Weinstin L, Swartz MN Pathogenic properties
  of invading microorganisms. In Sodeman WA Jr,
  Sodeman WA, eds. Pathologic Physiology
  Mechanisms of Disease. Philadelphia WB Saunders
  1974 472p.
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