Entamoeba Flashcards
Which parasite causes amebiasis?
Entamoeba histolytica
How is amebiasis spread?
fly vector
through water/food
sexually transmitted
person-person contact
Is Entamoeba histolytica a zoonosis?
no
What are the 6 species of human Entamoeba?
histolytica, hartmanni, gingivalis, dispar, coli, polecki
Which of these species can cause disease?
E histolytica, E coli, E gingivalis
What is the difference between E histolytica & E dispar?
one is pathogenic, the other is not. cannot be distinguished under the microscope
What is the infection dose?
can be as little as ONE cyst
What is the incubation period?
days-weeks depending on infective dose
Can cysts survive outside the host?
yes, under permissive temperatures and humidities
What are the two life cycle stages and what are their characteristics?
TROPHOZOITE:
fragile, must encyst to survive environment, strict anaerobe
CYST: resistant, sensitive to heat & freezing, can survive a few months in water, resistant to chlorine (use filtration)
What are some features of the nucleus?
numerous pores, inner surface membrane is lined with peripheral chromatin
What is the karyosome?
located in center of nucleus, probably contains DNA
What are chromatoid bars?
seen in cysts. blunt rods. Eventually disappear as cyst ages
contain ribo-nucleoproteins
What are the 5 types of vacuoles in Entamoeba?
phagocytic macropinocytic micropinocytic primary lysosomes secondary lysosomes
What are some risk factors for transmitting this disease?
poor areas, institutionalised populations, male homosexuals
Where do we see increased severity in the disease?
children, neonates, pregnancy, immunodepressed, alcoholics, elderly, malnutrition
With what do symptoms vary?
strain of E histolytica, number of cysts ingested, immune system of the host at the time of infection
What are some symptoms?
-intermittent diarrhea, cramps, vomiting, general malaise
results in 10-20% of infections
15-2 bowel movements per day with liquid feces & bloody mucus
rarely progresses to systemic abscesses (liver, brain, lungs)
What are the functions of the filopodia?
endocytosis attachment to substrate penetration of tissue release of cytotoxic materials cytolysis of cells
Describe the pathology
hydrolyse host tissues using their active cysteine proteases present on surface membrane of trophozoite
- causes lesions in caecum, appendix, or colon that may heal
- perforation of colon can lead to death
Define amoeboma
granuloma obstructing the bowel
How does Entamoeba live in the intestinal mucosa?
- can live & multiply indefinitely in large intestine
- invade mucous layer using lectin
- feed on starches & mucous secretions & interact metabolically with enteric bacteria
- initiate tissue invasion when they hydrolyse mucosal cells & absorb pre-digested products (no longer need to feed on bacteria)
How does Entamoeba affect the liver?
in 5% of infections
will form abscesses
trophozoites enter the mesenteric veinule & travel to liver via portal system
How does skin amebiasis occur?
through direct spread of a primary abscess
What are the 4 mechanisms by which Entamoeba are pathogenic?
- direct contact with host tissue using adhesion molecules
- release of soluble toxic metabolites after forming a hole in the target
- high enzymatic activity of vacuoles damages host cells
- cause inflammation, allergies, etc by releasing Ags
How does the immune system respond to Entamoeba?
- cytokine-activated macrophages can kill trophozoites via oxygen & oxygen independent mechanisms (direct contact activation)
- cytotoxic T cells activated, but not through direct contact
- Abs is NOT an active mechanism
- no TH2 response (no complement)
