21. Protozoa (Entamoeba) Flashcards
what disease is caused by Entamoeba histolytica?
Amoebiasis
what is amoebiasis/amoebic dysentery?
harbouring of protozoa E. histolytica inside the body with or without disease symptoms
what is the name of the invasive form of Entamoeba?
E. histoytica
what is the non-invasive form of Entamoeba?
E. dispar
where is Entamoeba histolytica most common?
in the tropics and subtropics (up to 60%)
________ diminishes with treatment, but _______ remains.
Mortality
morbidity
what is Amoebiasis’ rank in parasitic causes of death worldwide?
third parasitic cause of death after malaria and schistosomiasis
Entamoeba histolytica is a _______ virulent pathogen
facultative
what is the percent of infected people that actually get the disease?
10%
what are the two types of infection?
- extra-intestinal
- intestinal, mild to severe
what are the modes of transmission of Amoebiasis?
- Direct contact of person to person (fecal‐oral)
- Food or drink contaminated with feces containing the E. histolytica cyst
- Use of human feces (night soil) for soil fertilizer
- Transmission among homosexuals (oral‐anal)
- Contamination of food by flies and possibly cockroaches
what are the host specificities of Amoebiasis?
- All age groups affected
- No gender or racial differences
- Institutional, community living
- Disease severe in children, old, and pregnant women
what are the common environmental conditions that allow for prevalence of E. histolytica?
- Low socio‐economic
- Poor sanitation, sewage leakage
- Night soil for agriculture
- Seasonal variation
what are the two stages of the Entamoeba histolytica life cycle?
- trophozoite: vegetative stage
- cyst: infective stage
what are two environmental characteristics of the trophozoite stage?
- it must encyst to survive the environment. it is a fragile structure
- it is a strict anaerobe
what are the environmental characteristics of the cyst stage?
- resistant to the harsh conditions of the environment
- sensitive to heat and freezing; last a few months in water
- resistant to chlorine; remove via flocculation/filtration
which of the two stages is:
- passed in feces
- resistant
- infective
cyst
which of the two stages is:
- feeding
- motile
- replicative
trophozoite
how many cysts are necessary for infection?
only 1 cyst, making it the most efficient pathogenic protozoa
what is the name of the vegetative stage?
trophozoite
what is the morphology of the E. histolytica nucleus?
- spherical, containing central karyosome
- on the inner surface membrane, evenly distributed small chromatin dots
what is contained in the food vacuoles?
- leukocytes
- bacteria (which they feed on)
- maybe RBCs
what is the morphology of the pre-cyst stage of Entamoeba histolytica?
‐ Round or oval
- blunt pseudopodia
‐ Single nucleus present
what is the morphology of the cyst stage?
‐ Four nuclei are present in mature quadrinucleated cyst
‐ Glycogen mass & chromatoid bodies are present in immature cysts – disappear in mature ones
what is the morphology of the karyosome?
- located in the center of the nucleus
- probably contains DNA
what do the chromatid bars look like?
- they are seen in cysts
- they are blunt rods or splinter shape. They eventually disappear as the cyst ages.
what is the mitosome?
remnant mitochondrion
what kind of membrane does the mitosome have?
a double membrane, like mitochondria
how are proteins delivered to the mitosome?
by a targeting sequence of amino acids
what do mitosomes have different from mitochondria?
- they do not have genes within them
- the genes for the mitosomal components are contained in the nuclear genome
what is the morphology of the vacuoles?
- they occupy a great proportion of the cytoplasm.
- they may contain cellular debris, red blood cells, bacteria, or contain nothing
there are at least 5 types of vacuoles. what are the 5?
- phagocytic
- macropinocytic
- micropinocytic
- primary lysosomes
- secondary lysosomes
what are the two types of pathogenesis in E. histolytica?
- non-invasive
- invasive
what characterizes non-invasive ?
- ameba colony on intestinal mucosa
- asymptomatic cyst passer
- non‐dysenteric diarrhea, abdominal cramps, other GI symptoms
what characterizes invasive?
- necrosis of mucosa –> ulcers, dysentery
- ulcer enlargement –> dysentery, peritonitis
- metastasis –> extraintestinal amoebiasis
- cessation of cyst production
what does pathogenesis depend on?
- parasite virulence
- host resistance
- condition of the intestinal tract
where can the non-pathogenic parasites be found in the intestine?
in the lumen
where can the pathogenic parasites be found in the intestine?
trophozoites invade the intestinal mucosa
what do trophozoites produce? what pathology does this induce?
histolytic enzyme - it produces necrosis of the mucosa leading to the formation of flask-shaped ulcers
where do trophozoites exist in the pathogenic form?
in the base of the flask shaped ulcer
what is found in the pathogenesis of intestinal amoebiasis?
- Unique ability to hydrolyse host tissues with their active cysteine proteases present on the surface membrane of the trophozoite.
- Lesions are found in the caecum, appendix, or colon. They may heal. If perforation of the colon occurs, there is a peritonitis that can lead to death.
define Amoeboma
- granuloma obstructing the bowel due to the pathogenesis of E. histolytica
- is a mass under oedematous mucosa with:
- internal abscesses of necrotic tissue and amoebae
- outer firm nodular fibrous tissue
Amoeba cells can live and multiply indefinitely within the ________ of the mucosa of the large intestine
crypts
They are able to invade the ____________, which constitute a major non‐specific defense immune mechanism
mucous layer
They feed on _______ and __________________ and interacting metabolically with enteric bacteria
starches
mucous secretions
how do the parasites initate tissue invasion?
when they hydrolyse mucosal cells and absorb the pre-digested products
why do they hydrolyse mucosal cells?
so that they can absorb the pre-digested products and not have to feed on bacteria
how does the parasite adhere to the enterocyte?
Gal/GalNAc lectin
what does the activation of the amoebic virulence program consist of?
amoebic cysteine proteases
neutrophils will respond to the parasite. which cytokine causes their recruitment in this case?
IL-8 and other chemoattractants
what is the issue with neutroohil migration in amoebiasis?
they migration damages the epithelial barrier
how do the Amoeba invade between the cells?
they use their cysteine proteases to cleave extracellular matrix proteins and invade
what are the 4 types of pathologies/lesions found in the pathogenesis of E. histolytica? ***
- perforation, hemorrhage (rare)
- secondary infection
- amoeboma (rare)
- extraintestinal lesions
what characterises an Amoeboma?
- clinically stimulates a neoplasm
- intussusception
- obstruction
what is extra-intestinal amoebiasis?
- metastasis via blood stream
- primarily liver (portal vein)
– other sites less frequent
- amoeba‐free stools common
- high antibody titers
what are two extra-intestinal amoebiasis pathologies?
- pulmonary amoebiasis
- cutaneous amoebiasis
define pulmonary amoebiasis
- rarely primary
- rupture of liver abscess through diaphragm
- Secondary bacterial infections common
- fever, cough, pain
define cutaneous amoebiasis
- intestinal or hepatic fistula
- mucosa bathed in fluids containing trophozoites
–perianal ulcers
–urogenital (e.g. labia,
vagina, penis)
how is amoebiasis diagnosed?
- Microscopy: cannot distinguish cysts between E. histolytica and E. dispar
- Immuno‐fluorescence (IFA)
- PCR – used less frequently since DNA is less available if stool samples preserved in formalin for long periods
what consequence does infection have on the immune system?
long lasting antibody production
how does metronidazole, and tinidazole affect the parasite
- it is a tissue amoebicide
- it is very effecting in killing amoebas in the wall of the intestine, in blood in liver absesses
how does diluxanide furoate affect the parasite?
- it is a luminal amoebicide
- kills trophozoites and cysts in the lumen of the intestine
what are the methods of primary prevention of E. histolytica?
‐ Safe fecal disposal
‐ Safe water supply
‐ Hygiene
‐ Health education
how long do cysts remain viable in feces? in water?
- days
- longer periods
how are cysts killed?
- dryness
- heat over 55°C
- NOT chlorine
what are the methods of secondary prevention of E. histolytica?
- early diagnosis
- treatment
what is the main source of infection?
cyst passers (they pass many cyst and it only takes 1 to cause infection)
is there a human vaccine for E. histolytica?
no
how does the animal vaccine work?
Vaccinations using native and recombinant forms of the parasite Gal‐lectin have been successful in protecting animals in the lab against intestinal amoebiasis and amoebic liver abscess
What part of the body is inhabited by E. histolytica?
inhabits large intestine
what is the general life cycle of E. histolytica?
typical fecal-oral life cycle
