Amoebiasis

Question 1

What is the epidemiology of amoebiasis?

Answer 1

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

Question 2

How is amoebiasis transmitted?

Answer 2

Faecal-oral
Sexual

Question 3

Which intestinal amoeba is pathogenic?

Answer 3

E. histolytica

Question 4

Which entamoeba are microscopically identical to histolytica?

Answer 4

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

Question 5

Name the intestinal amoeba

Answer 5

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

Question 6

What is dientamoeba fragilis associated with?

Answer 6

IBS
Actually an amoebaflagellate

Question 7

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

Answer 7

Liquid - trophozoites
Solid - cysts

Question 8

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

Answer 8

E.dispar are not haematophagous

Question 9

Discuss the life cycle of entamoeba histolytica

Answer 9

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

Question 10

Discuss the clinical features of entamoeba histolytica

Answer 10

80% asymptomatic

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

Question 11

Name complications of amoebiasis

Answer 11

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

Question 12

What are 2 important features of amoebic liver abscesses?

Answer 12

Anchovy paste pus
Odourless

Question 13

Discuss the diagnosis of e.histolytica

Answer 13

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

Question 14

In which populations is e.histolytica serology not useful?

Answer 14

Endemic populations

Question 15

Discuss the treatment of e.histolytica

Answer 15

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

Question 16

Name predisposing factors to amoebiasis

Answer 16

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

Question 17

Discuss the features of e.histolytica trophozoites

Answer 17

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

Question 18

Discuss the features of e.histolytica cysts

Answer 18

Thick walled
Multiple nuclei

Question 19

Which cells can be confused with e.histolytica?

Answer 19

Histiocytes
Ganglion cells
Balantidium coli (larger, macro nucleoli)

Question 20

Discuss the histological features of e.histolytica affecting the colon

Answer 20

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

Question 21

Is HIV associated with increased e.histolytica infection?

Answer 21

No but assoc with increased severity

Question 22

What are the virulence factors of e.histolytica?

Answer 22

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

Question 23

Discuss the pathogenesis of e.histolytica

Answer 23

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

Question 24

Discuss the features of amoeboma

Answer 24

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

Question 25

Discuss the features of amoebic liver abscess

Answer 25

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

Question 26

Discuss the features of cutaneous amoebiasis

Answer 26

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

Question 27

Which organism causes amoebic meningoencephalitis?

Answer 27

Naegleria fowleri

Question 28

Which patients are usually infected by n. fowleri?

Answer 28

Young, healthy with a history of swimming

Question 29

Discuss the features of amoebic meningoencephalitis

Answer 29

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

Question 30

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

Answer 30

Meningitis extends along the spinal cord

Question 31

Which organism causes amoebic encephalitis?

Answer 31

Hartmanella (acanthamoeba)

Question 32

Discuss the features of amoebic encephalitis

Answer 32

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