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Flashcards in Entamoeba Deck (26):
1

Which parasite causes amebiasis?

Entamoeba histolytica

2

How is amebiasis spread?

fly vector
through water/food
sexually transmitted
person-person contact

3

Is Entamoeba histolytica a zoonosis?

no

4

What are the 6 species of human Entamoeba?

histolytica, hartmanni, gingivalis, dispar, coli, polecki

5

Which of these species can cause disease?

E histolytica, E coli, E gingivalis

6

What is the difference between E histolytica & E dispar?

one is pathogenic, the other is not. cannot be distinguished under the microscope

7

What is the infection dose?

can be as little as ONE cyst

8

What is the incubation period?

days-weeks depending on infective dose

9

Can cysts survive outside the host?

yes, under permissive temperatures and humidities

10

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)

11

What are some features of the nucleus?

numerous pores, inner surface membrane is lined with peripheral chromatin

12

What is the karyosome?

located in center of nucleus, probably contains DNA

13

What are chromatoid bars?

seen in cysts. blunt rods. Eventually disappear as cyst ages
contain ribo-nucleoproteins

14

What are the 5 types of vacuoles in Entamoeba?

phagocytic
macropinocytic
micropinocytic
primary lysosomes
secondary lysosomes

15

What are some risk factors for transmitting this disease?

poor areas, institutionalised populations, male homosexuals

16

Where do we see increased severity in the disease?

children, neonates, pregnancy, immunodepressed, alcoholics, elderly, malnutrition

17

With what do symptoms vary?

strain of E histolytica, number of cysts ingested, immune system of the host at the time of infection

18

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)

19

What are the functions of the filopodia?

endocytosis
attachment to substrate
penetration of tissue
release of cytotoxic materials
cytolysis of cells

20

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

21

Define amoeboma

granuloma obstructing the bowel

22

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)

23

How does Entamoeba affect the liver?

in 5% of infections
will form abscesses
trophozoites enter the mesenteric veinule & travel to liver via portal system

24

How does skin amebiasis occur?

through direct spread of a primary abscess

25

What are the 4 mechanisms by which Entamoeba are pathogenic?

1. direct contact with host tissue using adhesion molecules
2. release of soluble toxic metabolites after forming a hole in the target
3. high enzymatic activity of vacuoles damages host cells
4. cause inflammation, allergies, etc by releasing Ags

26

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)