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DTMH Block 3 > Amoebiasis > Flashcards

Amoebiasis Flashcards

1
Q

What is the epidemiology of amoebiasis?

A

NB in children <2y in developing countries
Developed countries usually travellers and immigrants

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2
Q

How is amoebiasis transmitted?

A

Faecal-oral
Sexual

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3
Q

Which intestinal amoeba is pathogenic?

A

E. histolytica

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4
Q

Which entamoeba are microscopically identical to histolytica?

A

E. dispar (common coloniser)
E. moshkovski (can cause diarrhoea)

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5
Q

Name the intestinal amoeba

A

Entamoeba (histolytica, dispar, moshkovski, coli, polecki, Bangladeshi)
Endolimax nana
Lodamoeba butschii
Dientamoeba fragilis

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6
Q

What is dientamoeba fragilis associated with?

A

IBS
Actually an amoebaflagellate

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7
Q

How does the ratio of cyst:trophozoite change depending on stool consistency?

A

Liquid - trophozoites
Solid - cysts

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8
Q

What is the difference between the trophozoites of e.histolytica and e.dispar?

A

E.dispar are not haematophagous

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9
Q

Discuss the life cycle of entamoeba histolytica

A
  1. Cysts ingested in faecally contaminated food or water
  2. Multiplication in the large intestine
  3. Excystation in small intestine
  4. Encystation in normal left colon
  5. Cysts excreted into stool
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10
Q

Discuss the clinical features of entamoeba histolytica

A

80% asymptomatic

Colitis
Abdominal pain
Watery diarrhoea
Dysentery
Inflammatory mass in colon wall
Tenesmus
PMN leucocytosis

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11
Q

Name complications of amoebiasis

A

Fulminant colitis
Toxic megacolon
Haematogenous spread to liver/lung/brain
Cutaneous
Ruptured abscesses (tamponade, etc)

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12
Q

What are 2 important features of amoebic liver abscesses?

A

Anchovy paste pus
Odourless

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13
Q

Discuss the diagnosis of e.histolytica

A

Microscopy of warm, fresh stool
Histology
Imaging
Antigen detection
PCR
Serology

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14
Q

In which populations is e.histolytica serology not useful?

A

Endemic populations

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15
Q

Discuss the treatment of e.histolytica

A

Treat ALL! Risk for invasive disease
Tissue amoebicide: flagyl
Luminal amoebicide: diloxanide/paramomycin/iodoquinol

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16
Q

Name predisposing factors to amoebiasis

A

Tropical climate
Malnutrition
Immunosuppression
Altered microbiome
Excessive alcohol
Poor hygiene
Contaminated water

17
Q

Discuss the features of e.histolytica trophozoites

A

Amoeboid
15-20 microns
Nucleus with central karyosome
Ingested RBCs
Intracytoplasmic glycogen (PAS positive)

18
Q

Discuss the features of e.histolytica cysts

A

Thick walled
Multiple nuclei

19
Q

Which cells can be confused with e.histolytica?

A

Histiocytes
Ganglion cells
Balantidium coli (larger, macro nucleoli)

20
Q

Discuss the histological features of e.histolytica affecting the colon

A

Small foci of ulceration (‘flask shaped ulcers’)
Geographic margins
Undermined edges
Shaggy exudate (basophils)

21
Q

Is HIV associated with increased e.histolytica infection?

A

No but assoc with increased severity

22
Q

What are the virulence factors of e.histolytica?

A

Galactose-inhibiting surface protein
Surface lectin
Pore forming peptides
Cysteine proteases

23
Q

Discuss the pathogenesis of e.histolytica

A
  1. Tissue invasion
    - cystine proteases degrade intestinal mucosa -> ECM digestion
    - cleavage of secretory IgA and IgG -> promoting infection spread
  2. Promotion of inflammatory mediators
    - complement activation
    - proteolytic cascade inhibitor
    - COX2 epithelial cell expression
    - prostaglandins, myeloperoxidase, IL8
    - increase epithelial permeability
24
Q

Discuss the features of amoeboma

A

5% of infections
Inflammatory thickening of bowel wall
Resembles malignancy clinically and radiologically

25
Q

Discuss the features of amoebic liver abscess

A

Necrotic center
Shaggy exudate with fibrin (anchovy paste)
No neutrophils
Variable trophozoites

26
Q

Discuss the features of cutaneous amoebiasis

A

Usually a complication via extension of infection (liver abscess to abdominal wall, rectal to perineal)
Painful, malodorous necrotic ulcer
Hyperplastic epidermis
Mononuclear inflammatory infiltrate
Trophozoites in dermis

27
Q

Which organism causes amoebic meningoencephalitis?

A

Naegleria fowleri

28
Q

Which patients are usually infected by n. fowleri?

A

Young, healthy with a history of swimming

29
Q

Discuss the features of amoebic meningoencephalitis

A

Soft, swollen brain
Purulent exudate on meningeal surface
Haemorrhage in affected cerebral tissue w/ thrombotic changes
Olfactory bulb/tract necrosis

30
Q

What is the feature of amoebic meningoencephalitis that is not usually found in other meningitic infections?

A

Meningitis extends along the spinal cord

31
Q

Which organism causes amoebic encephalitis?

A

Hartmanella (acanthamoeba)

32
Q

Discuss the features of amoebic encephalitis

A

More chronic than n.fowleri infection
Usually preceded by illness/trauma
Unrelated to swimming

33
Q
A

DTMH Block 3 (18 decks)

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