Lecture 7 Parasite diversity 6 Nematodes

Question 1

Why are nematodes so successful as parasites?

Answer 1

• different structure than other parasites

* wide variety of life cycles & transmission modes

Question 2

Nematodes:
• among most abundant animals ~75% _______________
• most diverse group of parasites 2000 plant nematodes alone!

Answer 2

free-living

Question 3

whatis the tough external coat nametodes shed as they grow?

Answer 3

cuticle

Question 4

what is the process of shedding cuticle or tough external coat?

Answer 4

molting/ecdysis

Question 5

What are the main characteristics of nematodes

Answer 5

tube within a tube
- pseudocoelom - hydrostatic skeleton 
-longitudinal muscles
-thick outer cuticle (mostly collagen) 
• intestine
-muscular pharynx & mouth
-mouth structure: buccal capsule with armament
-dieocious
-females prolific, lay many eggs

Question 6

General Nematode life cycles:

Answer 6

-transmitted as eggs, juveniles, via vectors

Question 7

Nematode reproduction & growth:

Answer 7

• recall – undergo molting
(clade Ecdysozoa)
-Juvenile (a.k.a. larval) stages
grow between molts
-can arrest development
under adverse conditions

Question 8

Ascaris lumbricoides affect

Answer 8

giant roundworm

Question 9

Juvenile stages have sheath and what is the name of the larvae.
_______stage juveniles most common arrested stage

Answer 9

sheath present
sheath gone
Dauer larvae
-infective stage juveniles most common arrested stage

Question 10

Describe what is infective stage of Trichostrongylus spp. and why arrest and why assume?

Answer 10

• ingest infective L3 stage
• exsheath & resume development
with specific stimuli present
-carbon dioxide 
-temperature
- pH

-hypobiosis in gut even more common if life cycle with intermediate hosts

Question 11

Strongyloides stercoralis:

Answer 11

• infection via
penetration or
autoinfection
• free-living or parasitic adults
• females produce eggs sexually or
via parthenogenesis

Question 12

Toxocara canis: different direct modes of infection

Answer 12

• life cycle depends on final host may age

–may enter hypobiosis

Question 13

Ancylostoma duodenale:

Answer 13

• one of the human “hookworms”

* multiple intermediate hosts for some nematode species

Question 14

Anisakis simplex:

Answer 14

• vector-mediated transmission
for some species
-filarial worms

Question 15

Onchocerca volvulus

Answer 15

black fly vector
river blindness
-little response to live microfilariae in blood or adults
-severe dermatitis in response to degenerating skin larvae

Question 16

Brugia malayi:

Answer 16

• consequences of adults in lymphatic tissue

1 species causing lymphatic filariasis (i.e. elephantiasis)

Question 17

Describe lymphatic filiariasis.

Answer 17

4. Vessels dilate
5. Polyps develop
6. Vessel wall hypertrophy
7. Granulomas & fibrosis
8. Lymph backup
9. Lymph node englargement

Question 18

• microfilarial morphology important for i.d.

Answer 18

• size small!
• sheath presence
• tail shape
• nuclei size & shape