Entamoeba histolytica

Transcription

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 1875 Lösch correlated dysentery with amebic trophozoites 1925 Brumpt proposed two species: E. dysenteriae and E. dispar 1970's Facultative Pathogenicity of Entamoeba histolytica 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 trophozoite immature cyst mature cyst

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 ulcers coalesce perforation of intestinal wall

13

14

15 Disease Manifestations ulcer enlargement severe dysentery perforation of intestinal wall peritonitis local abscesses 2 o 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 2 o 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)

21

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 pathogenecity virulence ability to cause disease (genetic component) 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.

26 E. histolytica vs E. dispar CRITERIA E. dispar E. histolytica In Vitro Culture xenic axenic ConA Agglutination - + Complement Resistance - + Zymodemes (isoenzymes) I & III II Numerous Antigenic Differences (eg., GIAP Epitopes) Numerous DNA Sequence Differences (eg., rrna) 2.2% sequence diversity RFLP/DNA Probes B133 ceh-np1 P145 ceh-p1

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 α-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 α-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

30

31 Prevalence Epidemiologic Risk Factors lower socioeconomic status crowding lack of indoor plumbing endemic area institutionalization communal living promiscuity among male homosexuals Severity Modified from Ravdin (1995) Clin. Inf. Dis. 20:1453 children, esp. neonates pregnancy and postpartum states corticosteroid use malignancy malnutrition

32 Clinical Syndromes Associated with Amebiasis Intestinal Disease asymptomatic cyst passer symptomatic nondysenteric infection amebic dysentery fulminant colitis! + perforation (peritonitis) ameboma (amebic granuloma) perianal ulceration Extraintestinal Disease liver abscess pleuropulmonary amebiasis brain and other organs cutaneous and genital diseases 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

33 Diagnosis Intestinal stool examination! cysts and/or trophozoites sigmoidoscopy! lesions, aspirate, biopsy antigen detection! histolytica/dispar Extraintestinal (hepatic) symptoms! history of dysentery! RUQ pain! enlarged liver serology (current or past?) imaging (CT, MRI, ultrasound) abscess aspiration! only select cases! reddish brown liquid! trophozoites at abscess wall

34 Antigen Detection Assay α-giap Monoclonal Antibodies mab E.h. E.d. 3F A F C G7 + - H Reactivities of mabs against E. histolytica and E. dispar Possible Outcomes and Interpretations capture/detection mabs 3F4/8A3 8C12/1G7 interpretation + + E. histolytica + - E. dispar - + inconclusive - - negative

35 Diagnosis Intestinal stool examination! cysts and/or trophozoites sigmoidoscopy! lesions, aspirate, biopsy antigen detection! histolytica/dispar Extraintestinal (hepatic) symptoms! history of dysentery! RUQ pain! enlarged liver serology (current or past?) imaging (CT, MRI, ultrasound) abscess aspiration! only select cases! reddish brown liquid! trophozoites at abscess wall

36 Treatment asymptomatic iodoquinol or paromomycin endemic areas? symptomatic metronidazole or tinidazole followed by lumenal agents drain liver abscess only with high probability of rupture! Control and Epidemiology 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