Amoebiasis Flashcards
What is the epidemiology of amoebiasis?
NB in children <2y in developing countries
Developed countries usually travellers and immigrants
How is amoebiasis transmitted?
Faecal-oral
Sexual
Which intestinal amoeba is pathogenic?
E. histolytica
Which entamoeba are microscopically identical to histolytica?
E. dispar (common coloniser)
E. moshkovski (can cause diarrhoea)
Name the intestinal amoeba
Entamoeba (histolytica, dispar, moshkovski, coli, polecki, Bangladeshi)
Endolimax nana
Lodamoeba butschii
Dientamoeba fragilis
What is dientamoeba fragilis associated with?
IBS
Actually an amoebaflagellate
How does the ratio of cyst:trophozoite change depending on stool consistency?
Liquid - trophozoites
Solid - cysts
What is the difference between the trophozoites of e.histolytica and e.dispar?
E.dispar are not haematophagous
Discuss the life cycle of entamoeba histolytica
- Cysts ingested in faecally contaminated food or water
- Multiplication in the large intestine
- Excystation in small intestine
- Encystation in normal left colon
- Cysts excreted into stool
Discuss the clinical features of entamoeba histolytica
80% asymptomatic
Colitis
Abdominal pain
Watery diarrhoea
Dysentery
Inflammatory mass in colon wall
Tenesmus
PMN leucocytosis
Name complications of amoebiasis
Fulminant colitis
Toxic megacolon
Haematogenous spread to liver/lung/brain
Cutaneous
Ruptured abscesses (tamponade, etc)
What are 2 important features of amoebic liver abscesses?
Anchovy paste pus
Odourless
Discuss the diagnosis of e.histolytica
Microscopy of warm, fresh stool
Histology
Imaging
Antigen detection
PCR
Serology
In which populations is e.histolytica serology not useful?
Endemic populations
Discuss the treatment of e.histolytica
Treat ALL! Risk for invasive disease
Tissue amoebicide: flagyl
Luminal amoebicide: diloxanide/paramomycin/iodoquinol
Name predisposing factors to amoebiasis
Tropical climate
Malnutrition
Immunosuppression
Altered microbiome
Excessive alcohol
Poor hygiene
Contaminated water
Discuss the features of e.histolytica trophozoites
Amoeboid
15-20 microns
Nucleus with central karyosome
Ingested RBCs
Intracytoplasmic glycogen (PAS positive)
Discuss the features of e.histolytica cysts
Thick walled
Multiple nuclei
Which cells can be confused with e.histolytica?
Histiocytes
Ganglion cells
Balantidium coli (larger, macro nucleoli)
Discuss the histological features of e.histolytica affecting the colon
Small foci of ulceration (‘flask shaped ulcers’)
Geographic margins
Undermined edges
Shaggy exudate (basophils)
Is HIV associated with increased e.histolytica infection?
No but assoc with increased severity
What are the virulence factors of e.histolytica?
Galactose-inhibiting surface protein
Surface lectin
Pore forming peptides
Cysteine proteases
Discuss the pathogenesis of e.histolytica
- Tissue invasion
- cystine proteases degrade intestinal mucosa -> ECM digestion
- cleavage of secretory IgA and IgG -> promoting infection spread - Promotion of inflammatory mediators
- complement activation
- proteolytic cascade inhibitor
- COX2 epithelial cell expression
- prostaglandins, myeloperoxidase, IL8
- increase epithelial permeability
Discuss the features of amoeboma
5% of infections
Inflammatory thickening of bowel wall
Resembles malignancy clinically and radiologically
Discuss the features of amoebic liver abscess
Necrotic center
Shaggy exudate with fibrin (anchovy paste)
No neutrophils
Variable trophozoites
Discuss the features of cutaneous amoebiasis
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
Which organism causes amoebic meningoencephalitis?
Naegleria fowleri
Which patients are usually infected by n. fowleri?
Young, healthy with a history of swimming
Discuss the features of amoebic meningoencephalitis
Soft, swollen brain
Purulent exudate on meningeal surface
Haemorrhage in affected cerebral tissue w/ thrombotic changes
Olfactory bulb/tract necrosis
What is the feature of amoebic meningoencephalitis that is not usually found in other meningitic infections?
Meningitis extends along the spinal cord
Which organism causes amoebic encephalitis?
Hartmanella (acanthamoeba)
Discuss the features of amoebic encephalitis
More chronic than n.fowleri infection
Usually preceded by illness/trauma
Unrelated to swimming
