Flukes Flashcards
(50 cards)
Name the two most common fluke species
- Fasciola hepatica
- Fasciola gigantica
Give examples of typical fluke characteristics
- Indirect lifestyle
- Dorso-ventrally flattened
- Hermaphrodite
- No body cavity
- Branches of the gut are visible
What are the major impacts of fluke on animal production?
- Growth rate
- Milk yield
- Wool and fibre
- Liver condemnation
How can you tell apart the eggs of Fasciola hepatic and Fasciola gigantics?
Fasciola gigantica eggs are larger and paler in colour
Describe the host cycle of Fasciola hepatica
- Indirect (includes more than one host)
- Definitive mammalian host where sexual reproduction occurs – where the adults reside
- Snail intermediate host is where asexual reproduction occurs
Give examples of the definitive mammalian host of Fasciola hepatica
- Ruminants
- Camelids
- Horses
- Humans (zoonosis)
Name and describe the intermediate host of Fasciola hepatica in the UK
Mud snail - Galba truncatula
- 5mm in size, burrow in mud so hard to find
Describe the eggs of F.hepatica when they are passed in the faeces
Undifferentiated so have a golden appearance with a very thin egg shell
Over how many weeks does the F.hepatica develop in the eggs on pasture?
2-4
When the F.hepatica eggs hatch, what happens, and how does it reach the snail?
The operculum on the egg opens up and the miracidium is released and it is covered in a ciliated outer surface, these cilia help it swim to come into contact with the snail
Describe how the miracidium are adapted to reach and infect the snail?
- Miracidium are motile, photosensitive and they can detect the chemical signature of the snail
- The miracidium are short lived (24hrs) so they have to rapidly swim to the snails to infect them
- They burrow into the foot of the snail to gain access to the body cavity
What happens to the miracidium when they have infected the snail?
They lose the outer ciliated surface – they are now called sporocysts
Describe the reproduction of sporocysts
From one sporocyst we can get multiple rediae (asexual reproduction, clonal expansion), which are genetically identical
Further asexual reproduction of the rediae produces?
Cercariae
How do cercariae continue the life cycle?
- This stage burrows out of the snail
- When they come into contact with a solid surface e.g. vegetation, they encyst
What is involved in the encystation of a cercariae?
Lose their tail, surround themselves with a carbohydrate and protein rich coating which protects the parasite when its out on pasture – now named a metacecariae
Name the stage of the F.hepatica that is infective to the mammalian host
Metacecariae
How do metacecariae infect the mammalian host, and which tissues do they migrate to?
- ingested with vegetation
- exist as juveniles in the gut
- there is a cap on the metacecariae that opens up and releases the parasite – they exist within the intestine in the duodenum, they pass through the peritoneal cavity in search of the liver, where they migrate
How long does it take the metacecariae to migrate to the liver?
6-8 days
Once the metacecariae have reached the liver, what happens next?
- By secreting proteolytic enzymes they make holes in and migrate through the liver
- After 10-12 weeks the parasites are continuing to grow in size, once they are adults they migrate into the bile ducts- they are sexually mature adults producing eggs at this point
What is the name of the diseases caused by migrating fluke?
Fasciolosis
What are the two forms of Fasciolosis?
Acute
Chronic
The type of Fasciolosis disease is determined by?
The number of metacercariae ingested and the time period over which they are ingested
Describe the pathogenesis of Acute fasciolosis
- Large numbers of immature flukes migrating through the liver, cause lots of damage
- Multifocal necrotic or haemorrhagic tracts throughout the liver
- Inflammation, liver enlargement, fibrosis
