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Parasite Immunology > Schistosomiasis > Flashcards

Schistosomiasis Flashcards

1
Q

What three species of Schistosoma are of vast medical significance?

A

Schistosoma mansoni

Schistosoma japonicum

Schistosoma haematobium

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2
Q

Where in the body do adult Schistosoma worms typically reside?

A

Adult worms live within the veins that drain certain organs of their host’s abdomen. Each of the three main species have distinct preferences.

  • S. haematobium lives mainly in the veins of the urinary bladder plexus
  • S. mansoni prefers the portal veins draining the large intestine
  • S. japonicum is concentrated in the veins of the small intestine
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3
Q

Within which veins does S. haematobium typically reside?

A

Schistosoma haematobium typically resides in the veins of the urinary bladder plexus.

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4
Q

Within which veins does Schistosoma mansoni reside?

A

S. mansoni resides within the portal veins that drain the large intestine.

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5
Q

What veins do Schistosoma japonicum worms typically reside?

A

S. japonicum worms are concentrated in the veins of the small intestine.

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6
Q

How many people worldwide suffer from severe Schistosomiasis?

A

20 million people

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7
Q

What does Schistosoma mean?

A

Split body- referring to the gynecophoral canal of the male

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8
Q

What types of eggs does Schistosoma mansoni produce?

A

Laterally spined eggs.

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9
Q

Where is Schistosoma japonicum distributed?

A

Japan, China, Taiwan, the Philipines and SE Asia.

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10
Q

What term describes the ventral, longitudinal groove on male Schistosoma?

A

Gynecophoral canal.

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11
Q

Where does the female Schistosoma reside when moving?

A

The gyncecophoral canal of the male.

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12
Q

What does Schistosoma do to improve motility upstream from smaller veins?

A

The female Schistosoma positions itself within the gynecophoral canal of the male.

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13
Q

Where does copulation between male and female Schistosoma take place?

A

Within the gynecophoral canal.

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14
Q

Where are the eggs of Schistosoma deposited?

A

Within the small venules of the host.

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15
Q

What obstacle must eggs traverse before they can be expelled by the host?

A

The wall of the venules (small vein) and gut or bladder.

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16
Q

What process aids egg expulsion from the host?

A

The endothelial lining of the venule moves over the Schistosome eggs to exclude them from the lumen.

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17
Q

What processes may the worm complete to aid transport of the eggs to the gut or bladder lumen?

A

It may exploit host immune responses.

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18
Q

What process occurs once a Schistosoma egg has been forced out of the venule?

A

The expelled egg stimulations the formation of a granuloma (mass of cells containing eosinophils, plasma cells and macrophages).

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19
Q

Once the Schistosome granuloma has formed where does it move to?

A

The granuloma, containing the Schistosome egg moves to the intestinal or bladder lumen.

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20
Q

Once the Schistosome granuloma reaches the bladder or intestinal lumen what occurs?

A

The granuloma disperses and the egg contained within is expelled in the urine or faeces.

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21
Q

What fraction of Schistosome eggs are retained and not expelled from the host via urine or faeces?

A

Around 2/3 of eggs are not excreted and accumulate within the bladder or gut wall.

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22
Q

What stimulus triggers the hatching of the Schistsome egg?

A

Contact with fresh water releases free-swimming miracidia.

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23
Q

Once the miracidia are released in water what process occurs?

A

Cilia activation continues which allows the miracidium to enter a high spin state.

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24
Q

Once the miracidia reaches its high spin state what occurs?

A

Osmotically controlled vents open which allows the miracidium to emerge.

25
Q

How long can a miracidium swim for to find a host?

A

6 hours maximum

26
Q

What tropism do miracidium possess?

A

Schistsome miracidia are positively phototropic

27
Q

What are the important intermediate snail hosts for Schistosoma haematobium?

A

Bullinus and Physopsis

28
Q

What are the important intermediate snail hosts for Schistosoma mansoni​?

A

Biomphalaria spp

29
Q

What are the important intermediate snail hosts for Schistosoma japonicum​?

A

Oncomelania spp

30
Q

When a miracidium penetrates a snail host what occurs?

A

The miracidium sheds its epithelium and enters a new stage of development, the mother sporocyst

31
Q

How long does the mother sporocyst stage last?

A

2 weeks

After two weeks the mother sporocyst gives birth to daughter sporocysts that migrate to other organs within the snail.

32
Q

How long does the mother sporocyst produce daughter sporocysts for?

A

6 weeks

33
Q

What emerges from the daughter sporocysts?

A

Tail forked (furcocercous) CERCARIAE

34
Q

How long does it take between initial penetration of the snail by miracidium and the emergence of cercariae from daughter sporocysts?

A

~ 4 weeks

35
Q

How do cercariae penetrate human skin?

A

The cercariae lack an oral sucker

They have a head organ with penetration glands and a ventral sucker covered in spines.

36
Q

How long do the cercariae survive in water?

A

The cercariae survive for 1-3 days and swim to the surface and sink the bottom in cycles.

37
Q

Once the cercariae come into contact with a human host how do they find a suitable penetration site?

A

They creep until they find a suitable penetration site.

38
Q

What attracts the cercariae to the human host?

A

Cercariae are attracted to skin secretions, particularly arginine

39
Q

What skin secretion is particularly attractive to free-swimming cercariae?

A

Arginine

Stimulation of the cercariae allows it to produce arginine itself via the postacetabular glands, attracting other cercariae to the vicinity.

40
Q

Via which gland do cercariae produce arginine?

A

Postacetabular gland

41
Q

Why does the cercariae produce its own arginine when it is stimulated by host skin arginine?

A

Increased arginine attracts more cercariae to the penetration site.

42
Q

How does the cercariae complete penetration?

A

The cercariae can penetrate the surface within seconds and through the epidermis in less than 30 minutes.

Vigorous wiggling and secretion of products from the head organ assist penetration.

43
Q

What happens to the cercariae tail after penetration?

A

The tail is lost.

44
Q

Once the cercariae lost their tails where do the schistosomules move to?

A

Within 24 hours the schistosomules enter the peripheral circulation and are swept to the heart.

45
Q

Once the schistosomules leave the right heart where to they go?

A

They attempt to move through the pulmonary capillaries to gain access to the left heart and circulation.

46
Q

What percentrage of schistosomules are lost trying to migrate through lung capillaries?

A

Up to 70%

47
Q

What route must schistosomules take to reach the liver for further growth?

A

Schistosomules must enter the mesenteric arteries and traverse the intestinal capillary bed to reach the liver via the hepatoportal system.

48
Q

Where do schistosomules continue their development after migrating through the heart, lungs and circulation?

A

The liver via the mesenteric arteries and intestinal capillaries.

49
Q

How long do the schistosomules develop within the liver sinusoids?

A

3 weeks

50
Q

Once developed within the liver sinusoids what do the young worms do?

A

The worms pair up and migrate to the gut or bladder wall (depending on species)

51
Q

Where do the schistosomes produce eggs?

A

Within the gut or bladder wall (depending on species)

52
Q

How long does the prepatent period last? (time between infection and detection of eggs in excreta)

A

5-8 weeks

53
Q

How long can adult schistosomes live for?

A

20-30 years

54
Q

What happens to unpaired female worms?

A

They do not become sexually mature and may starve.

55
Q

When a female pairs with a male what process assists growth?

A

Growth stimulating factors are released that may assist the immature female to pump blood into her intestine.

56
Q

What is required to stimulate Schistosome development?

A

Host immune cues

TNF stimulates egg production

IL7 and thyroxin are required for growth

CD4 lymphocytes produce important immune signals for the parasite

57
Q

What is the main epidemiological factor in Schistosomiasis?

A

Human waste in water

58
Q

What is responsible for all the pathogenesis in Schistosomiasis?

A

The Schistosome eggs, the worms do not contribute to pathogenesis.

59
Q

How are the Schistosome eggs packaged to traverse the gut or bladder wall?

A

They are contained within a granuloma

Parasite Immunology (5 decks)

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