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Parasitology > 14. Tissue nematodes > Flashcards

14. Tissue nematodes Flashcards

1
Q

What are the 3 tissue nematodes that we saw?

A
  • Onchocerca volvulus
  • Dracunculus medinensis
  • Wucheria bancrofti
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2
Q

what is the common name for the disease caused by Onchocerca volvulus?

A

River blindness

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3
Q

what is the common name for Dracunculus medinensis?

A

Guinea worm

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4
Q

what is the common name for the disease caused by Wuchereria bancrofti?

A

Elephantiasis

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5
Q

what is required for the Onchocerca volvulus life cycle?

A
  • humans

- black flies

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6
Q

what is required for the Dracunculus medinensis life cycle?

A
  • humans

- Cyclops (an aquatic invertibrate)

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7
Q

how do humans aquire Onchocerca volvulus?

A

via fly bite

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8
Q

how do humans acquire Dracunculus volvulus?

A

ingestion of water containing Cyclops

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9
Q

which are the tissue nematodes that are transmitted by arthropods?

A
  • Wuchereria bancrofti (Elephantiasis)

- Onchocerca volvulus (River blindness)

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10
Q

which are the tissue nematodes that are transmitted by copepods?

A
  • Dracunculus medinensis (Guinea worm disease)
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11
Q

what are the three parasites that can cause lymphatic filariasis?

A

the three filarial worms:

  • Wuchereria bancrofti
  • Brugia malayi
  • Brugia timori
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12
Q

what us caused by chronic infection by a filarial worm?

A

elephatiasis

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13
Q

what is the vector for Wuchereria bancrofti?

A

mosquito, most of which feed at night

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14
Q

what is the preference of mosquito vectors?

A

they prefer human blood

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15
Q

what is special about the nocturnal microfilariae?

A

they appear in the peripheral circulation at night (so that they can be easily picked up by mosquitos)

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16
Q

which are the “threadlike” nematodes

A

Wuchereria

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17
Q

where are Wuchereria nematodes located?

A

in the lumen of lymphatic vessels

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18
Q

what is the name of Wuchereria larvae?

A

microfilariae

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19
Q

what is oviviparous and which parasite uses this reproductive strategy?

A
  • mode of reproduction in which embryos develop inside eggs that are retained within the mother’s body until they are ready to hatch
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20
Q

how many microfilariae can be release by the female in a day?

A

10,000

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21
Q

where do the worms most commonly live in the body?

A

in the lymphatics of the lower and upper extremities and in male genitalia

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22
Q

what are microfilariae encased in?

A

a sheath of chitin - which is possibly a remnant of an eggshell

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23
Q

when and where do the microfilariae migrate in the body?

A

from the lymphatic circulation to the blood circulation and are typically present in large numbers between 10pm and 6am

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24
Q

where can the microfilariae be found in the day?

A

in the capillaries of the lungs

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25
Q

how long do microfilariae live?

A

1.5 years

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26
Q

how are microfilariae transmitted?

A
  • by mosquito bite, they penetrate the mosquitoes stomach wall and locate the thoracic flight muscles
  • when infectious, they locate to the mosquito biting mouth parts are are deposited on the skin NEXT to the wound
27
Q

how many molts do microfilariae have?

A

2 molts

28
Q

what is the infective stage of the microfilariae?

A

L3

29
Q

how long can the adults live in the host?

A

5-8 years, infections lasting 40y have been reported

30
Q

do all patients with chronic exposure to infective larvae develop over clinical disease?

A

no

31
Q

what are the three phases of wuchereria infection in the clinical disease?

A
  • asymptomatic phase
  • inflammatory (acute) phase
  • obstructive (chronic) phase
32
Q

what is the asymptomatic phase

A

high microfilariae infection where individuals show no symptoms of being infected

33
Q

what is the inflammatory (acute) phase

A
  • the antigens from the female adult worms elicit inflammatory responses
  • worms in the ;ymph channels disrupt the flow of the lymph
  • the individual will exhibit fever, chills, skin infections, painful lymph nodes and tender skin of the extremity
  • symptoms often lessen after 5-7 days
34
Q

what is the obstructive (chronic) phase

A
  • marked by elephantiasis
  • lymphatic dysfunction causing lymphedema and elephantiasis and scrotal elephantiasis
  • scar formation on the affected areas
  • thickening of the skin
35
Q

how is Wuchereria infection diagnosed?

A
  • blood smear, provided that the sample is taken at the time in the day where microfilariae can be found
  • PCR for filarial DNA
36
Q

what is the disease associated with Oncocerca volvolus?

A

Oncocerciasis (river blindness)

37
Q

what are the four parasites that cause subcutaneous filariasis?

A
  • Oncocerca volvulus
  • Dracunculus medinensis (the Guinea worm)
  • Loa loa (the African eye worm)
  • Mansonella streptocerca
38
Q

which parasite does not have any reservoir hosts?

A

Oncocerca

39
Q

what is the vector for Oncocerca?

A

various species of blackfly

40
Q

what do blackflies AND mosquitos require to mature their eggs?

A

bloodmeal

41
Q

where do the larvae of the blackflies live?

A

in fast-flowing streams and rivers

42
Q

River blindness is the ______ leading cause of blindness in the developing world

A

fourth

43
Q

__________ has reduced onchocerciasis incidence and prevalence by more than 90% in certain regions

A

Ivermectin program

44
Q

which nematodes lie intertwined within each other in subcutaneous fibrous nodules

A

Oncocerca

45
Q

where are Oncocerca micrfilariae produced?

A

in the subcutaneous fibrous nodules

46
Q

what is a main consideration with treatment of Oncocerca microfilariae?

A

the dead microfilariae induce inflammatory reactions

47
Q

what are the clinical features of oncocerciasis?

A
  • dermatitis
  • eye lesions
  • oncocercomas
48
Q

what causes the lesions seen in oncocerciasis?

A

as a consequence of cell mediated immunity

49
Q

what is keratitis?

A

results from the accumulation of punctate opacities in the cornea arising from immunopathologic damage to microfilariae in the eye

50
Q

how is Oncocerca diagnosed?

A
  • examination of a piece of skin

- serological tests that measure IgG antibodies for onchocerciasis are sensitive but the specific is poor

51
Q

what is the drug of choice for Oncocerca

A

Ivermectin

52
Q

what disease do Drancunculus medinensis cause?

A

Guinea worm disease

53
Q

what is guinea worm disease

A

a disease unique to humans, can be eradicated by providing safe water supply (prevents D. medinensis from completing its life cycle)

54
Q

where can Dracunculus adult worms be found?

A

they dwell primarily in the subcutaneous tissues, usually in the lower extremeties

55
Q

what do both sexes of Dracuncula have in common?

A

they both have acutely curved tails, to anchor to tissues

56
Q

does the female drancunculus release larvae or eggs?

A

the female releases motile larvae

57
Q

what happens to Dracunculus larvae after they are released by the female?

A

they are ingested by copepods and develop into L3

58
Q

what is the infective stage of Dracunculus

A

L3

59
Q

what is the path of Dracunculus in the infected human?

A

they are ingested, and the larvae are released where they penetrate the wall of the intestine. larvae migrate in the connective tissue and molt twice before adult

60
Q

where do gravid females migrate?

A

through subcutaneous tissues into the extremities, causing ulcers that burst when coming in contact with water

61
Q

what is the pathology of Dracunculus infection?

A
  • multiple cutaneous blisters and ulcers
  • allergic rxn in advance of rupture
  • substantial disability
  • secondary bacterial infections! (tetanus, gangrene, and death)
62
Q

how are the worms removed in a Drancunculus infection?

A

a person will wind the worm on a think stick until it is completely extracted - carefully in order to not break the worm

63
Q

give 4 reasons why Dracunculus infection has successful eradication efforts.

A
  • no human carrier state beyond the 1-year incubation period
  • Transmission is seasonal
  • cases are easily detected
  • methods for controlling are relatively simple (water purification)

Parasitology (27 decks)

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