Entamoeba

Question 1

Which parasite causes amebiasis?

Answer 1

Entamoeba histolytica

Question 2

How is amebiasis spread?

Answer 2

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

Question 3

Is Entamoeba histolytica a zoonosis?

Answer 3

no

Question 4

What are the 6 species of human Entamoeba?

Answer 4

histolytica, hartmanni, gingivalis, dispar, coli, polecki

Question 5

Which of these species can cause disease?

Answer 5

E histolytica, E coli, E gingivalis

Question 6

What is the difference between E histolytica & E dispar?

Answer 6

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

Question 7

What is the infection dose?

Answer 7

can be as little as ONE cyst

Question 8

What is the incubation period?

Answer 8

days-weeks depending on infective dose

Question 9

Can cysts survive outside the host?

Answer 9

yes, under permissive temperatures and humidities

Question 10

What are the two life cycle stages and what are their characteristics?

Answer 10

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)

Question 11

What are some features of the nucleus?

Answer 11

numerous pores, inner surface membrane is lined with peripheral chromatin

Question 12

What is the karyosome?

Answer 12

located in center of nucleus, probably contains DNA

Question 13

What are chromatoid bars?

Answer 13

seen in cysts. blunt rods. Eventually disappear as cyst ages

contain ribo-nucleoproteins

Question 14

What are the 5 types of vacuoles in Entamoeba?

Answer 14

phagocytic
macropinocytic
micropinocytic
primary lysosomes
secondary lysosomes

Question 15

What are some risk factors for transmitting this disease?

Answer 15

poor areas, institutionalised populations, male homosexuals

Question 16

Where do we see increased severity in the disease?

Answer 16

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

Question 17

With what do symptoms vary?

Answer 17

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

Question 18

What are some symptoms?

Answer 18

-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)

Question 19

What are the functions of the filopodia?

Answer 19

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

Question 20

Describe the pathology

Answer 20

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

Question 21

Define amoeboma

Answer 21

granuloma obstructing the bowel

Question 22

How does Entamoeba live in the intestinal mucosa?

Answer 22

• 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)

Question 23

How does Entamoeba affect the liver?

Answer 23

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

Question 24

How does skin amebiasis occur?

Answer 24

through direct spread of a primary abscess

Question 25

What are the 4 mechanisms by which Entamoeba are pathogenic?

Answer 25

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

Question 26

How does the immune system respond to Entamoeba?

Answer 26

• 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)