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BSC Zoology - Parasitology > 13. Nematodes infective larvae cont'd > Flashcards

13. Nematodes infective larvae cont'd Flashcards

1
Q

what are the nematodes with infective larvae (L3)?

A

Necator amercanus
Ancylostoma duodenale
Strogyloides stercoralis
Trichinells spiralis

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2
Q

what is the world’s largest intracellular parasite?

A

Trichinella spiralis

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3
Q

what is the distribution of Trichinella spiralis

A

worldwide

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4
Q

which areas are the exception, and do not have Trichinella?

A

Puerto rico

Australia

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5
Q

what is special about the life cycle of Trichinella spiralis?

A

the DH and the IH are the same individual

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6
Q

is T. spiralis host-specific?

A

NO

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7
Q

what is the size of the female worm of T. spiralis? male worm?

A

female: 3mm x 36µm
male: 1.5mm x 36µm

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8
Q

what is the size of the new born larvae?

A

80µm x 7µm

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9
Q

how many molts does Trichinella larvae undergo before developing into the adult?

A

4

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10
Q

how long does it take for T. spiralis to do 4 molts?

A

30 hours

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11
Q

where are larvae released from (T. spiralis)?

A

Nurse cells in the stomach

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12
Q

what is the habitat of the adults (T. spiralis)?

A

the small intestine

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13
Q

what is the domestic cycle?

A
  • They are all zoonoses with humans becoming infected incidentally (i.e. eating raw or undercooked meat, pork) and not playing a role in the life cycle
  • You can have the animals infecting themselves
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14
Q

where is sylvatic cycle found?

A
  • temperate zone
  • tropic zone
  • arctic zone
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15
Q

How is trichinellosis acquired?

A

by ingesting meat containing cysts (encysted larvae) of Trichinella

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16
Q

what indices the releasing of larvae from their cysts?

A
  • After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms
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17
Q

where do the larvae encyst?

A

in striated muscle

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18
Q

what larval stage is the one to encyst in striated muscle?

A

L1

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19
Q

which Trichinella species never encysts?

A

Trichinella pseudospiralis

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20
Q

how long does it take for encystment? how long are they viable for?

A

4-5 weeks, and several years

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21
Q

how is the cycle of Trichinella continued?

A

ingestion of the encysted larvae

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22
Q

what is the human’s role in the life cycle?

A

they are accidentally infected when they eat improperly processed meat

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23
Q

Where are Trichinella spiralis found?

A

in all tissues - eventually they reach the skeletal muscle

24
Q

what are some of the most commonly invaded muscles of Trichinella spiralis?

A

Eye, tongue, masticator muscles, diaphragm, intercostal muscles, and the muscles found in arms and legs

25
Q

Do nurse cells form in the heart?

A

NO

26
Q

Do nurse cells form in the nervous system?

A

NO

27
Q

why are the juveniles like a virus?

A
  • they penetrate individual cells
  • they subvert and redirect the host cell activities to their own survival
  • they alter gene expression of the host cell of the contractile fibre to that of a nurse cell –> they remodel what the cell is supposed to be doing
28
Q

what is a nurse cell?

A
  • The nurse cell is a unique consequence of the host cell’s association with the infectious L1 larva of Trichinella spp.
  • Its function us thought to nourish as well as protect it from host immune responses
  • it is to make sure it survives and gets nourished as well – nurses the parasite
29
Q

how long can the nurse cell-parasite complex can survive in the human host? how?

A

30 years - the worm immuno-supresses the host

30
Q

what are the two distinct phases of the overall process of the nurse cell

A
  1. de-differentiation

2. re-differentiation

31
Q

what are the steps leading to nurse cell survival?

A
  • Larvae enter the muscle fibre cell
  • Fibre loses its myofilaments
  • Fibre mitochondria degenerates
  • Fibre nuclei enlarges
  • Fibre smooth endoplasmic reticulum increases
  • Encapsulation of the unit with collagen
32
Q

describe nurse cell formation?

A
  1. Larvae enters muscle, muscle proteins “leak” into bloodstream
  2. Mitochondrial damage – they start to break down, and nothing will have energy so everything that happens after this is coming from the larval stage of the parasite
  3. Secretion of parasite proteins – no longer a skeletal muscle, more a nerve cell
  4. DNA synthesis and nuclear enlargement – starts to produce specific proteins that it needs at that point
  5. Collagen type IV synthesis has a critical role in the regulation of angiogenesis
  6. Collagen type VI synthesis: a non-fibrillar collagen and forms a microfilament network – start remodelling the whole cell type
  7. Induction of vascular endothelial growth factor (VEGF) – triggers …
  8. Angiogenesis – nerve blood vessels that will surround the nerve cell and keep it alive
33
Q

what is bad about angiogenesis

A

angiogenesis is required for spread of a tumour or metastasis

34
Q

What is VEGF?

A

a signal protein produced by cells that stimulated angiogenesis (marker to know that angiogenesis has started)

35
Q

what is the major reservoir for T. spiralis?

A

pig

36
Q

what is the major reservoir for T. pseudospiralis?

A

pig

37
Q

What species of Trichinella has no freezing resistance and a high reproductive capacity?

A

T. spiralis

38
Q

What species of Trichinella has freezing resistance and low reproductive capacity?

A

T. native
T. britovi
T. nelsoni
T. pseudospiralis

39
Q

What species of Trichinella has no cycts/nurse cells formation?

A

T. pseudospiralis

40
Q

what is the stichosome?

A

The stichosome is a multicellular organ that apparently functions as a secretory gland and storage organ

41
Q

what makes up the stichosome?

A

a single row of 45-55 cells called stichocytes

42
Q

what do the antigens in the stichocytes cross-react with? what hypothesis was formulated in relation to this?

A

antigens present in the excretion-secretion products of living muscle larvae;

that secretory-excretory substances from the stichocytes not only are immunogenic but mediate alteration of host gene expression during the formation of the nurse cell

43
Q

what do the stichocytes have?

A
  • α and β stichocytes

- mitochondria, golgi-like apparatus, RER, 2 types of secretory granules

44
Q

which 3 stages cause pathology in Trichinella?

A
  • intestinal stage
  • migrating larvae
  • muscle
45
Q

what is the pathology of the intestinal stage of Trichinella?

A

Worms migrating in the intestinal epithelium cause traumatic damage to the tissues. Inflammation causes nausea, vomiting, sweating, and diarrhea

46
Q

what is the pathology of the migrating larvae stage of Trichinella?

A
  • Juveniles damage blood vessels resulting in localized edema. They may cause pneumonia, myocarditis, encephalitis, eye damage, etc.
    • L1, L2 and L3 are the things that will cause the most damage
    • By going in and out of the cells, you cause the rupturing of cells and thus the edema
47
Q

what is the pathology of the muscle stage of Trichinella?

A
  • Formation of the nurse cell causes muscle pain, difficulty breathing, and swallowing. Presence of eosinophilia and edema in tissues
    • Depending on how many of these larvae, you might have muscle pain
    • A heavier burden – pain
48
Q

what accompanies invasions of muscles by formation of nurse cells?

A

an intense inflammatory reaction

49
Q

what raises the inflammatory reaction?

A

the release of the secretory-excretory antigens - the nurse cells are being developed and you have this release from the worm

50
Q

can adult worms be detected in a stool specimen?

A

NO

51
Q

can migrating juveniles be detected?

A

NO

52
Q

how are muscle nurse cells detected?

A
  • by biopsy

- muscle larvae can be seen easily by crushing the tissue between microscope slides

53
Q

is serology a good method for diagnosis of Trichinella?

A

NO - false positives

54
Q

what is PCR used for in Trichinella diagnoses?

A

epidemiology

55
Q

what is given to relieve symptoms of Trichinella?

A

Analgesics and immunosuppressive drugs like corticosteroids

56
Q

which drugs are used to eliminate the adult host from the intestine?

A
  • mebendazole

- albendazole

57
Q

are drugs recommended to eliminate nurse cells?

A

NO - only by surgery

BSC Zoology - Parasitology (27 decks)

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