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BSC Zoology - Parasitology > 05. Trematodes > Flashcards

05. Trematodes Flashcards

1
Q

What are trematodes commonly referred to as?

A

flukes

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2
Q

What is the taxonomy of D. caninum? (recall from last lecture)

A

Order Cyclophillydea
Family Dipylidiidae
Genus Dipylidium
Species caninum

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3
Q

What is the common name of D. caninum? (recall from last lecture)

A

Dog/cat tapeworm

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4
Q

All tapeworms are ____-parasites

A

endoparasites

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5
Q

are trematodes only found in the intestine?

A

NO - they can inhabit many organs

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6
Q

What organ system do Schistosoma spp. infect?

A

vasculature of the gastro-intestinal or genitourinary systems

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7
Q

What organ system do Fasciolopsis, Heterphyes heterophyes, and related organisms infect?

A

They are intestinal flukes, they infect the GI tract

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8
Q

What organ system do Clonorchis sinensis, Fasciola hepatica and Opisthorcis infect?

A

The liver

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9
Q

What organ system do Paragonimus westermany and related species infect?

A

They are lung flukes, they infect the lungs and other organs such as the CNS

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10
Q

Why is the life cycle of a digenetic trematode complex?

A

It involves at least 2 hosts

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11
Q

What kind of animal is the first intermediate host of the digenetic trematode?

A

A mollusc (usually a snail)

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12
Q

What kind of animal is the DH of the digenetic trematode?

A

A vertebrate

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13
Q

Do you always have a redia?

A

NO

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14
Q

Do you always have a sporocyst?

A

YES

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15
Q

What are characteristic of the adult digenetic trematode?

A

the two suckers

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16
Q

What are the names and functions of the two suckers in a digenetic trematode?

A

Oral sucker - for attachment and feeding (mostly feeding)

acetabulum (ventral sucker) - for attachment only, there is no internal opening

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17
Q

What type of muscle is found on the suckers?

A

smooth muscle - found in bands on the suckers for strong attachment

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18
Q

What kind of body wall do digenetic trematodes have?

A

tegument

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19
Q

what are the two layers of tegument

A

syntegument and cytotegument

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20
Q

Describe the syntegument (outer layer)

A
  • it contains mitochondria, secretory bodies and occasional spines
  • it is a chemical layer that lies on top of outer cell membrane
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21
Q

Describe the cytotegument (inner layer)

A
  • consists of cell bodies beneath the tegument
  • each cell contains a nucleus and organelles (such as the rER and golgi)
  • separated from syntegument by layers of tegumental muscle
  • connected to syntegument by cytoplasmic bridges
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22
Q

what are the functions of the cytotegument?

A
  • involved in the production of mucus
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23
Q

What are the functions of the tegument? (3)

A

1- osmoregulation and excretion
2- synthesis and secretion of mucus (to protect against host enzymes)
3- Absorption of nutrients for trematode nutrition

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24
Q

What is the morphology of the adult trematode digestive tract?

A
  • muscular scmooth muscle creates sucking action
  • short esophagus leads to 2 long, blind-ending cecum
  • no anus
  • proteins are digested in the lumen of the intestine and absorbed through the intestinal epithelium
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25
Q

What is the parenchyma?

A

loosely arranged cells filling space between the organs

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26
Q

What is the role of the excretory system?

A

to remove excess water that has diffused into the worm

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27
Q

What is the role of flame cells?

A
  • they are something that cestodes do not have, making the digenetic trematodes different in that respect
  • they are cells (having a nucleus) that contain beating flagella that create a hydrostatic pressure, which draws pressure from the parenchyma into the collecting duct
  • at the posterior end of the worm there is an excretory bladder
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28
Q

Describe the nervous system of the digenetic trematode

A

there is a ladder type system consisting of a ganglionic mass, lateral nerve trucs, and connecting commissures

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29
Q

Describe the sense organs of adult digenetic trematodes

A

they are at the cellular level within the tegument

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30
Q

Describe the sense organs of the larval stages of digenetic trematodes

A
  • the sense organs are well-developped
  • they seem to be able to differentiate between light and dark
  • they have a much more elaborate nervous system because they need to be able to sense if someone is swimming in the water and to be able to swim to that area
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31
Q

Describe the sexual morphology of adult digenetic trematodes

A
  • the reproductive system is elaborate and specialized

- almost all adult digenetic trematodes are hermaphroditic (except Schisto)

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32
Q

What are the three possible ways that trematodes reproduce?

A

1) Some worms contain both male and female sexual orgas and are capable of auto-fetilisation
2) Others contain both male and female organs but meet up with another worm for cross fertilization
3) Schistosomes are unique among the trematodes in that that have distinct male and female worms. They live together as a long-term life unit, with the larger male surrounding the thinner female worm

33
Q

What is the sexual morphology of Schistosoma spp.

A

Sexually dimorphic/diecious

34
Q

Describe the male reproductive system of digenetic trematodes

A
  • There are 2 testes
  • the sperm ducts consist of 2 vas efferentia which join to form a vas deferens
  • the vas deferens leads to a cirrus sac (cirrus pouch)
    slide 19
35
Q

What is an important taxonomic character of the male reproductive system of a digenetic trematode?

A

The shape and position of the testes

36
Q

What is an important taxonomic character of the female reproductive system of a digenetic trematode?

A

the shape and position of the ovary in relation to the testes

37
Q

Describe the female reproductive system of the digenetic trematode

A

a single ovary produces eggs which pass along the oviduct to the ootype

38
Q

Describe the constituents of the digenetic trematode egg

A
  • well-developped egg shell enclosing the ovum
  • one or more sperm cells
  • and a number of vitelline cells
39
Q

What is an opperculum?

A

a “lid” at one end of the egg

40
Q

T/F the digenean egg is usually opperculate

A

True, except Schisto

41
Q

What develops following fertilization?

A

an embryo of miracidium

42
Q

What characters are used for identification of digenetic trematode eggs

A

Size, morphology and color

43
Q

Which digenean species that infect humans have spines?

A

Schistosoma mansoni and Schistosoma heamatobium

44
Q

What are the 3 species of Schistosoma that infect humans?

A

Schostosoma japonicum, Schistosoma mansoni and Schistosoma heamatobium

45
Q

What is an example of a species where the egg is ingested before hatching?

A

Dorocoelium dendriticum (lancet fluke) - the eggs hatch inside and it penetrates the intestinal epithelium to invade the molluscan tissues

46
Q

What is an example of a species where the egg hatches in water before ingestion?

A

Fasciola hepatica (liver fluke)

47
Q

What are important factors for an external egg hatching?

A
  • Light
  • Temperature
  • Change in osmotic pressure
48
Q

What is released upon hatching of the egg?

A

The miracidium

49
Q

What are the organs of locomotion of the miracidia of the digenetic trematode?

A

cilia

50
Q

Is the miracidium usually free swimming?

A

YES

51
Q

Who is the target of the miracidium?

A

the primary (possibly the only) IH of the parasite

52
Q

Who is the IH of digenetic trematodes?

A

molluscs (snails usually)

53
Q

What is the role of the germinal mass?

A

development of the parasite in the snail

54
Q

What is ALWAYS the first development after the hatching of the miracidium?

A

the miracidium develops into the early sporocyst stage

55
Q

What characterizes the development into the early sporocyst stage?

A

the loss of ciliated cells, the penetration glands and the apical gland

56
Q

When does the development of the miracidium into early sporocyst stage usually occur?

A

at the site of penetration of the mollusc (1st IH)

57
Q

what does the early sporocyst develop into and in which location?

A

it develops into the mother sporocyst

58
Q

What occurs after the development of the mother sporocyst?

A

The germ cells in the mother sporocyst multiply and develop into the daughter sporocysts, which are essentially the same as their parent sporocysts

59
Q

In what case would the redia not develop?

A

if the daughter sporocysts are formed

60
Q

What is an example where the redia stage is absent?

A

Schistosomes, there are two generations of sporocysts in the snail host

61
Q

What is the advantage of the asexual reproduction in the snail?

A

increases the potential of reproduction of the organsims. a single moracidium can give rise to hundreds of thousands of cercariae

62
Q

What is the second larval form to develop in the molluscan host?

A

the redia

63
Q

How are redia similar to sporocysts?

A

Redia are similar to sporocysts, containing germinal masses withing a fluid-filled cas, which may develop into either second generation daughter redia, or more commonly into the final larval stage within the mollusc, the cercaria

64
Q

How are redia different from sporocysts?

A

Redia differ from sporocysts in that they are much more active and aggressive and possesses a mouth and a simple gut (a little more advanced)

65
Q

What the order of the digestive tract in digenetic trematode larvae?

A

mouth –> large muscular pharynx –> opens into a simple intestine

66
Q

What do many redia have behind the mouth?

A

a ridge-like collar

67
Q

What is below the ridge-like collar?

A

the birth canal opening from which either cercariae or daughter redia emerge

68
Q

What stage emerges from the mollusc in dingenetic trematode larvae?

A

in most cases, the cercarial stage - the infective form for the vertibrate host

69
Q

What are the types of cercariae? (4)

A
  • Gymnocephalus
  • Trichocercous
  • Furocercous
  • Microcercus
70
Q

Are cercaria released from the mollusc usually free swimming?

A

yes

71
Q

What happens to the tail of the cercaria after they penetrate skin?

A

they shed the tail

72
Q

Are the cercaria free swimming?

A

YES

73
Q

In what case would the cercariae penetrate the DH directly?

A

Scistosoma

74
Q

in what case will a mesocercaria develop?

A

If there are two or three IH and the cercaria penetrates the second IH to form the resting stage (mesocercaria)

75
Q

in what case will a metacercaria develop?

A

If there are three IH and the cercaria penetrates the third IH, where the paracite encysts to form metacercaria

76
Q

What are the infective stages?

A

metacercaria and cercaria themselves

77
Q

What are the possible final IHs? (3)

A
  1. a fish
  2. an arthropod
  3. another mollusc
78
Q

What parasite uses a fish as a final IH?

A

Opisthorchis sinensis

79
Q

What parasite(s) use(s) an arthropod as a final IH?

A

Dicrocoelium dendriticum - uses an ant

Paragonimus westermani - a crustacean

BSC Zoology - Parasitology (27 decks)

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