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54 Cards in this Set
- Front
- Back
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What is the difference between diarrhea and dysentery?
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Dysentery: has blood and mucus
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What are the causes of traveller's diarrhea?
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Bacterial or viral
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What are parasitic protozoa?
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Microsopic single cell organism
45,000 species of protooa, most of them are parasites |
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What are some pathogenic intestinal protozoa?
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Entamoeba histolytica
Giardia lambia Balentidium coli.... |
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Are all intestinal protozoa pathogenic?
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No, some are commensal
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What disease does Entamoeva histolytica cause?
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Amebiasis
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How many species of Entamoeba are there?
What are they? |
6 species:
E. histolytica E. dispar E. hartmanni E. coli E.gingivalis E. polecki |
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What's the difference between E. histolytica anc E. dispar?
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E. dispar is NOT pathogenic and non-invasive
E. histolytica is invasive |
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What's the difference between E. histolytica and E. dispar?
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E. dispar is NOT pathogenic and non-invasive
E. histolytica is invasive |
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διά τὸν
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acc ->because of
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Can these 2 types of entamoeba be distinguished microscopically?
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No
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How can we distinguish between these 2 protozoans?
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Use PCR, look at them at the DNA level
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παρα τὸν
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with; besides
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How many ppl are currently infected with E. histolytica?
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500 million
-> 70,000-100,000 deaths per year |
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What is the mode of infection for E. histolytica?
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Water
Food Flies can act as passive vectors Can be sexually transmitted Person-person contact |
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Where is this parasite found?
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Regions with poor sanitation: Mexico, Central & South America, Africa, South Asia
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What is the only source for this parasite?
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Humans, .: not a zoonotic parasite
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How is this parasite transmitted?
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Oral-fecal
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What are the type of amoebiasis?
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1) Asymptomatic carrier state: 90%
2) Acute amoebic dysentery: damaged intestine, 9% 3) Amoebic liver abscess: liver damage, 1% 4) Amoeboma: granuloma found in stomach <1% |
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What is the % of E. histolytica in developing countries?
In developed countries? |
Developing: ~10%
Developed: ~1% |
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Describe the Entamoeba histolytica life cycle
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Pick up cysts
Go to stomach Go to colon Can encyst once in the colon --> can become trophozoite Lives and multiplies in the colon |
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What is the infective dose of E. histolytica?
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1 cyst is all thats needed
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What is the incubation period for this parasite?
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From a few days to a few weeks, depending on the infective dose
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How long can a cyst survive?
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Can survive a long time
-->Weeks if at the appropriate T and humidity --> Cysts are very stable |
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What are the morphological differences between the trophozite stage and cyst stage of E. histolytica?
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Trophozoite: Has ingested RBCs; nucleus with central karyosome and finely divided peripheral chromatin; pseudopod
Cyst: 1-4 ring-like nuclei with finely divided peripheral chromatin; cyst wall and round shape |
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What are the cytoplasmic structures of E. histolytica?
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Nucleus
Endosome Vacuoles |
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Describe the nucleus
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Nuclear mb contains many pores
Inner surface mb is lined with peripheral chromatin |
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Describe the endosome
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Located in the center of the nucleus
Probably contains DNA |
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Describe the parasite vacuoles
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Occupy a freat proportion of the cytoplasm
Vary between 5-9 um in size May contain cellular debris, RBCs and bacteria (==> Feeding) |
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Describe how the vacuole works
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1) Bacterium becomes attached to mb evaginations called pseudopodia
2) Bacterium ia ingested, forming phagosome 3) Phagosome fuses with lysosome 4) Lysosomal enz digest captured material 5) Digestion products are released from cell |
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Where do amebas live in the body?
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Multiply indefinitely within the crypts of the mucosa of the large intestine
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How do the amoeba get there?
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Invade the mucouse layer (part of the non-specific defense immune mech)
Feed on starches and mucous secretion and interacting metabolically with enteric bacteria Initiate tissue invasion when they hydrolyse mucosal cells and absorb the pre-digested products --At this stage they no longer need to feed on bacteria |
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What do trophozoites have that might halp in pathogenesis?
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Filopodia
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How do these filopodia help in pathogenesis?
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Endocytosis
Attachment to substrate Penetration of tissue Release of cytotoxic materials Cytolysis of cells |
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Do most ppl infected with E. histolytica show symptoms?
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No, most ppl are asymptomatic
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What symptoms do most ppl present?
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Diarrhea to dysentery, with blood and mucous
Fever Abdominal pain |
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What are tools to diagnose this type of infection?
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Amoebic (hematophagous trophozoites and cysts) in stool
Patchy inflammation seen on colonoscopy Serology: Ab in serum Stool PCR: detection of parasite DNA in stool Ag capture: detection of parasite ptn in stool |
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What does E. histolytica do when it gets to the mucosa?
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Can ingest RBCs
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What pathology does it cause in the intestine?
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Hydrolyzes host tissue using their own parasitic active proteases that are on the surface mb of the trophozoite
Lesions can be found in the cecum, appendix or colon (may heal) Perforation of the colon Amoeboma |
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What happens if the colon is perforated?
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Can lead to serious problems
Can lead to sepsis (since bacteria will escape) as well as peritonitis that can lead to death |
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What is amoeboma?
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Granuloma that obstructs the bowel
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What pathology can be caused in the liver?
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Hepatic amebiasis: takes place when trophozoites enter the mesnteric veinule and travel to the liver through the hepatic portal system
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Is liver pathology common?
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No, only 5-10% of infections will affect the liver
Can cause abscesses |
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How long do the symtpoms of this usually last?
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2-4 weeks
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What is a good way to prevent this infection?
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Wash hands
Don't eat raw vegetables when travelling Boil water |
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How do you treat this infection?
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Use different antibacterials like metronidazole or tinidazole, followed by iodoquinol or paromycin
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What are the mechanisms of cytotoxicity of this parasite?
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Direct contact with the host tissues
Release of soluble toxic metabolites High enzymatic activities of amoebas Interfering with the immune response of the host |
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What is an example of direct contact with the host tissues?
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Adherewnce to the host cell by the release of adhesin molecules
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What is an example of release of soluble toxic metabolites?
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Amoebapore are capable of forming a hole in the target cell
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What is an example of high enzymatic activities of the amoebas?
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Enz released by the parasite damaging the host cell
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How can the parasite interfere with the host IR?
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Ag released by the amoeba can lead to: Inflam reaction
Allergies Immunosuppression Over stimnulation of cytokines Formation of immune complexes Formation of autoAb |
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What are the ways for the immune system to kill the amoebic cell?
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1) Macrophages activated by cytokines can kill Entamoeab trophozoites
The killing mechanism is contact-dependent and is mediated by O2 and O2-independent mechanisms 2) Tcyts are active and their activities depend on release of lympho-cytotoxins, since direct contact of amoebas with cytotoxic lymphosytes are not always active 3) Ab don't seem to play a major protective role |
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Is ADCC (Ab dependent cell-mediated cytotoxicity) an important mech to kill the parasite?
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No
-->haven't seen lysis of amoebas through immune serum alone or C' .: Th2 type of immune response does not play a major role vs amoebiasis |
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How does amebiasis of the skin occur?
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Direct spreading of primary abscess
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