Platyhelminthes

Question 1

What are three types of platyhelminthes?

Answer 1

Monogenea
Digenea (flukes and trematodes)
Cestodes

Question 2

How do monogeneans live?

Answer 2

Ectoparasites of fish and amphibia.

Can develop as endoparasites eg in frog bladder to avoid dessication.

Question 3

What are some basic features of monogeneans?

Answer 3

Holdfast/Haptor - hooks and suckers
Anterior end modified for feeding and adhesion
Blind ending gut
Tegument allows for excretion
Forms whole daughter inside ‘Russian doll parasite’

Question 4

What are some basic features of digeneans?

Answer 4

>1 host
one host is usually a snail
ventral and oral suckers 
2 blind ending branches of gut
egg < cilliated miracidium containing germinal cells < invades snail forms sporocyst < redia, feeding stage, released cercariae < encysts forming metacercaria < Adult in vertebrate def. host.

Question 5

Features of cestodes

Answer 5

Small head/scolex with suckers and spines to hook onto wall of gut.
Long segmented body/strobila, new segments form at head
Each segment had male and female sex organs
No mouth or gut, body segments can just absorb food and excrete waste
Can identify species from scolex.

Question 6

What is Fasciola hepatica?

Answer 6

Liver rot of sheep
Digenean
Zoonotic disease
Found in ireland

Question 7

Lifecycle of Fasciola hepatica

Answer 7

1. Adult flukes 1.5cm in bile duct of sheep
2. pass eggs in feces
3. Miracidia hatch in damp pasture and swim to snail
4. cercariae released from snail and encyst on grass. Eaten by sheep

Question 8

What caused Schistosomiasis?

Answer 8

3 digenean species: Schistosoma mansoni, S. japonicum, S. haematobium.
transmitted by feces or urine.
Male worms- 15mm, female - 20mm. Live in blood vessels surrounding bladder/gut.

Question 9

S. mansoni life cycle

Answer 9

1. Female enclosed in gynacophoric canal of male, travel through blood.
2. release eggs - 300 per day. Inflammation as penetrate into bladder or through gut wall. Eggs identified by spine.
3. Miracidium develops - first swimming stage, infects snail
4. Forms sporocysts and cercariae released. each snail released 1000 carcariae. steong tail, good swimmers. Swims towards warmth and sweat secretions of human. Bores into human. Covers surface with liver proteins to hide from immune system

Question 10

What is Swimmers itch?

Answer 10

Infection of wrong host, eg Bird Schistosoma cercariae infecting humans.
Skin rash, controlled by immune system.No worms develop.

Question 11

How is Schistosomiasis controlled?

Answer 11

Common in African countries

Praziquantel - oral drug, requires treatment as child, 30p per child per year. Long programme needed

Question 12

What digenean uses a terrestrial snail as an intermediate host?

Answer 12

Dicrocoelium dendriticum

Question 13

Life cycle of Dicrocoelium dendriticum

Answer 13

1. (fully embryonated) Eggs pass out of sheep in feces.
2. Hatch when ingested by terrestrial snail.
3. After 90 days, cercariae ejected with slime ball
4. On vegetation, eaten by ant.
5. Metacercariae in ants develop and control beaviour. Ants climb up grass blades and bite on them. At night cant open mouth due to cold. Eaten by sheep.
6. Mature flukes in sheep bile duct.

Question 14

Which parasite causes pulsating colours on snail eyes?

Answer 14

Leucochloridium paradosum

Bird def host, snail int.