Intro to Parasitology

Question 1

Morphological features of nematodes

Answer 1

• Long (mm to >50cm long)
• Tough elastic cuticle
• Muscular pharynx
• Nerve ring around pharynx and four longitudinal nerves
• Separate sexes
• Female worms (blunt, pointed tail)
• Male worms (spicules ± ‘bursa’ – expansion of cuticle covering male tail in bursate worms; absent in non-bursate nematodes)

Question 2

Feeding behaviour of nematodes

Answer 2

• Some swallow gut ingesta and/or host secretions
• Others suck a plug of mucosa into their buccal cavity (or mouth; plug feeders), leaving a circular ulcer
• Others bury their heads deep into the mucosa and suck blood

Question 3

Life cycle of nematodes

Answer 3

Egg ingested by dog  L1  L2  L3  L4  somatic migration -> Adult worm (or L5) -> egg ingested

Question 4

Morphological features of cestodes

Answer 4

Chain (strobila) of progressively-maturing independent reproductive units (segments or proglottids)
Anchored to intestinal wall by hold-fast organ (scolex, head-end)
Pseudophyllidean tapeworms – scolex has 4 longitudinal ‘grooves’ (important in tropics/subarctic regions)
Cyclophyllidean tapeworms – scolex often has hooks (armed)(global importance)

Question 5

Cestode segments

Answer 5

Each segment – male and female reproductive organs
Mature segments drop off adult tapeworm daily
Mature (gravid) segment >100,000 eggs
Eggs immediately infective (contain tapeworm larva = oncosphere or hexacanth embryo with six hooks)

Question 6

Feeding behaviour of cestodes

Answer 6

No alimentary tract
Absorb nutrients across body surface covered by a tegument (many minute projections, microthreces, increase the surface area)

Question 7

Cestode life cycle

Answer 7

Indirect life cycle, e.g. Echinococcus granulosus
egg -> sheep (intermediate host) -> hydatid cysts (metacestode stage) -> sheep dog (final host) -> eggs

Question 8

Examples of epidemiological relationships

Answer 8

Predator-prey (e.g. cat eating infected mouse)
Accidental (e.g. horse eating infected pasture mites)
Irritation (e.g. infected flea – swallowed during grooming)

Question 9

Types of metacestode

Answer 9

Vary in the number of developing scolices they carry:
Cysticercus (one scolex)
Coenurus (many scolices)
Hydatid cyst (thousands of scolices)

Question 10

Morpological features of trematodes

Answer 10

Typically flat, leaf-like worms (few mms to several cms long)
Oral and ventral suckers
Mouth leads from oral sucker to blind-ending caecae
Most species hermaphrodite, but individuals cross-fertilize
Flukes covered by a metabolically, highly-active tegument – important role in evasion of host immune response

Question 11

Trematode feeding behaviour

Answer 11

suck blood/ingest tissue debris (pumped into caecae)

Question 12

Trematode life cycle

Answer 12

Indirect life cycle, e.g. Fasciola hepatica
Fluke egg (containing a miracidium larvae) -> mud snail (intermediate host) -> sporocyst, redia, cercaria, metacercaria stages -> sheep (final host) -> fluke egg

Question 13

What are anthropods?

Answer 13

Great diversity, e.g. insects & acarines
Separate sexes
Insects (3 body divisions, compound eyes, 3 pairs of legs, may have wings)
Acarines (2 body divisions, simple eyes, 4 pairs of legs, no wings, small size)

Question 14

Anthropod feeding behaviour

Answer 14

Mouthparts show a variety of adaptations:
Sucking up liquefied food
Sucking blood
Chewing skin debris
Not feeding at all

Question 15

Anthropod life cycle

Answer 15

insects:
Simple metamorphosis: egg – nymph – adult (e.g. lice)
Complex metamorphosis: egg – larva – pupa – adult (e.g. fleas, flies)

acarines:
Egg – larva – nymph – adult

Question 16

Protozoa morphological features

Answer 16

Protozoa are motile, unicellular organisms with a nucleus, endoplasmic reticulum, mitochondria, Golgi body and lysosomes
Great diversity, e.g. Entamoeba, Leishmania, Trypanosoma

Question 17

Protozoa feeding behaviour

Answer 17

Pinocytosis (liquid droplets or small particles) or phagocytosis (larger particles)

Question 18

Protozoa life cycle

Answer 18

Variations in:
-Complexity
Asexual reproduction alone (e.g. simple binary fission, Babesia)
Asexual and sexual reproduction (e.g. Eimeria, Toxoplasma)
-Number of hosts

Question 19

Protozoa variations in host number

Answer 19

HOMOXENOUS life cycle (=direct), e.g. poultry coccidia (final host, chicken)
HETEROXENOUS life cycle (=indirect), e.g. Babesia spp (final host, tick; intermediate host, cattle)
FACULTATIVELY HETEROXENOUS life cycle (may be >1 host, but not essential), e.g. Toxoplasma (final host, cat; other hosts, any warm-blooded animal)