1. Entamoeba histolytica
cosmopolitan distribution
no animal reservoirs
facultative pathogen
most clear the infection spontaneous in 6-12 months with mild or no symptoms
can cause a serious invasive disease
worldwide incidence = %
estimated that 10% of world’s population may be infected
50 million cases invasive amebiasis/yr
100,000 deaths/yr

2. Facultative Pathogenicity of Entamoeba histolytica
1875 Lösch correlated dysentery with amebic trophozoites
1925 Brumpt proposed two species: E. dysenteriae and E. dispar
1970's biochemical differences noted between invasive and non-invasive isolates
80's/90's several antigenic and DNA differences demonstrated
rRNA 2.2% sequence difference
1993 Diamond and Clark proposed a new species (E. dispar) to describe non-invasive strains
1997 WHO accepted two species

3. Entamoeba histolytica
Life Cycle

4. Excystation cyst wall disruption ameba emerges nuclear division (48)
cytoplasmic division (8 amebala)
trophozoites colonize large intestine
feed on bacteria and debris
replicate by binary fission

5. Excystation cyst wall disruption ameba emerges nuclear division (48)
cytoplasmic division (8 amebala)
trophozoites colonize large intestine
feed on bacteria and debris
replicate by binary fission

6. Encystation trophozoite rounds up secretion of cyst wall
aggregation of ribosomes (= chromatoid bodies)
2 rounds of nuclear division (14 nuclei)
survive weeks to months

7. immature cyst
mature cyst
trophozoite

8. Pathogenesis of Amebiasis
NON-INVASIVE
ameba colony on intestinal mucosa
asymptomatic cyst passer
non-dysenteric diarrhea, abdominal cramps, other GI symptoms
INVASIVE
necrosis of mucosa  ulcers, dysentery
ulcer enlargement  dysentery, peritonitis
metastasis  extraintestinal amebiasis

9. ulcers with raised borders
little inflammation between lesions

10. ‘flasked-shaped ulcer’
trophozoites at boundary of necrotic and healthy tissue
trophozoites ingesting host cells
dysentery (blood and mucus in feces)

11. ‘hematophagous’ trophozoites

12. Lateral and Downward Expansion of Ameba into Lamina Propria
localized sloughing
perforation of intestinal wall
ulcers coalesce

15. Disease Manifestations
ulcer enlargement  severe dysentery
perforation of intestinal wall  peritonitis
local abscesses
2o bacterial infections
occasional ameboma (=amebic granuloma)
cessation of cyst production
ameboma = inflammatory thickening of intestinal wall around the abscess (can be confused with tumor)

16. Extraintestinal Amebiasis
metastasis via blood stream
primarily liver (portal vein)
other sites less frequent
ameba-free stools common
high antibody titers
Amebic Liver Abscess
chocolate-colored ‘pus’
necrotic material
usually bacteria free
lesions expand and coalesce
further metastasis, direct extension or fistula

17. Pulmonary Amebiasis rarely primary
rupture of liver abscess through diaphragm
2o bacterial infections common
fever, cough, dyspnea, pain, vomica

18. Cutaneous Amebiasis intestinal or hepatic fistula
mucosa bathed in fluids containing trophozoites
perianal ulcers
urogenital (eg, labia, vagina, penis)

19. Cutaneous Amebiasis intestinal or hepatic fistula
mucosa bathed in fluids containing trophozoites
perianal ulcers
urogenital (eg, labia, vagina, penis)

20. Cutaneous Amebiasis intestinal or hepatic fistula
mucosa bathed in fluids containing trophozoites
perianal ulcers
urogenital (eg, labia, vagina, penis)

22. Facultative Pathogenicity
85-90% of infected individuals are asymptomatic
~10% of the symptomatic will develop severe invasive disease

23. Molecular Epidemiology
molecular probes used to survey for E. dispar and E. histolytica
E. dispar ~10-fold > E. histolytica
discrete endemic pockets of E. histolytica
many asymptomatic E.h. infections
~10% of the E.h. infections are associated with invasive amebiasis
~25% seropositive for E. histolytica in endemic areas

24. a pathogen has an inherent ability to break host cell barriers
pathogenecity
ability to cause disease
(genetic component)
virulence
relative capacity to cause disease (degree of pathology)
a pathogen has an inherent ability to break host cell barriers
virulence usually correlates with ability to replicate within host
various degrees of virulence may be exhibited depending on conditions

25. contact-dependent killing of epithelial cells
breakdown of tissues (extracellular matrix)
secreted proteases?
contact-dependent killing of neutrophils, leukocytes, etc.

27. Galactose Inhibitable Adherence Protein
trophozoites adhere to mucins, epithelial cells, leukocytes, etc
mediated by galactose-inhibitable lectin activity
lectin activity due to surface protein (GIAP)
170 kDa heavy chain mediates binding (multigene family)
35 kDa light chain anchor to membrane
a-GIAP Abs abrogate complement resistance
~85% identity between Eh and Ed
Are there differences in adherence?
after contact the target cell is lysed and phagocytosed by the trophozoite

28. Host Cell Lysis and Phagocytosis
Amebapore
pore-forming peptide
potent anti-bacterial activity
located in vacuoles, not secreted
Eh and Ed sequences are 95% identical
GluPro change breaks a-helix
Ed had 80% less activity than Eh

29. Entamoeba Proteases
Eh expresses and secretes higher levels of cysteine proteases
6 cys-protease genes (ehcp1-6)
ehcp1 and 5 are missing in Ed
90% inhibition of ehcp5 did not affect trophozoite mediated destruction of host cell monolayers

32. Intestinal Symptoms range mild to intense transient to long lasting
nondysenteric
diarrhea
cramps
flatulence
nausea
dysenteric
blood/mucus in stools
cramps/pain
tenesmus
ameboma
palpable mass
obstruction

34. Antigen Detection Assay

36. Control and Epidemiology
Treatment
asymptomatic
iodoquinol or paromomycin
endemic areas?
symptomatic
metronidazole or tinidazole
followed by lumenal agents
drain liver abscess
only with high probability of rupture!
avoid fecal-oral transmission
not normally associated with travelers diarrhea
> 1 month stay
institutions
mass drug treatment little affect
 staff and improved housing conditions lowers prevalence
male homosexuals
40-50% in NYC and SF during late 70’s
lower since AIDS/safe sex