Fasciola hepatica المتورقة الكبدية

-External structure:

1-Dark red in colour.
2-Approx. 3cm long and 1.5cm wide.
3-Body is flat and leaf like.
4-Body has an oral sucker that surrounds the mouth and a ventral sucker, both serve to attach the fluke to the tissue of the primary host
5-Body is surrounded by a thick protective cuticle.
6-Cuticle bears many spines to attach to the wall of the primary host.
7-There is a genital pore for reproduction between the two suckers.

-The liver fluke is hermaphrodite, i.e. it contains both male and female reproductive organs in the one body.

-Life cycle:

It involves two different hosts:
A primary host (sheep or cattle) and a secondary host (fresh water snail/mud snail)
1. Sexual reproduction - in the bile duct of the primary host.
(a) A single fluke can produce up to 20,000 fertilised eggs per day.
(b) The eggs are released from the primary host with the faeces.
2. Finding a secondary host - external environment
(a) Light, moisture, and a temperature above 10 degrees Celcius are required for the fertilised eggs to hatch into the first larval stage, the miracidium.
(b) The miracidium has cilia to help it swim and has 24 hours to find a snail.
3. Asexual reproduction (polyembryony) - in the secondary host.
(a) The miracidium uses its spine to penetrate the snail.
(b) Each miracidium develops into a sporocyst.
(c) Each sporocyst produces many redia asexually.
(d) Each redia can produce many rediae.
(e) Each redia can produce many cercaria.
(f) The cercaria leave the snail.
4. Finding a primary host - external environment.
(a) The cercarium swims by means of its tail to a blade of grass.
(b) It forms a cyst about 0.25mm in size.
5. The adult matures - In the primary host.
(a) The encysted cercaria are ingested by the primary host.
(b) An immature fluke emerges from the cyst, burrows through the intestinal wall and migrates to the liver.
(c) Young flukes feed and grow in the liver.
(d) When sexually mature the adults enter the bile duct and copulate.

Economic and medical importance:

The liver fluke can have some serious effects on the host:

1-The liver of the primary host will be damaged, this can cause liver rot.
2-Excretory products of the fluke have a toxic effect on the host.
3-The wool of infected sheep is very dry and of poor quality.
4-In cattle milk yields are reduced.
5-Loss of weight for all animals.
6-Fertility is reduced for all animals.
7-Resistance to disease is reduced.
8-Severe infection can result in death

-Adaptations of the Liver Fluke:

1. Suckers: Attachment to the primary host.
2. Spines: Attachment to the primary host.
3. Cuticle: Protection.
4. Hermaphrodite:
(a) Any fluke can produce a fertilised egg (doubles the population).
(b) Cross fertilisation can take place leading to increased variation.
(c) Self fertilation can take place.
5. 20,000 eggs produced per day: To increase chances of some surviving and gaining access to the secondary host.
6. Light needed for eggs to hatch:
Ensures eggs only hatch once outside the primary host. This gives the miracidium the full 24 hours to locate a snail.
7. Cilia on miracidium: Enables it to swim to secondary host.
8. Spine on miracidium: To help penetrate the snail.
9. Asexual reproduction in the water snail: Increase chances of some cercaria gaining access to the primary host.
10. Tail on cercarium: Enables it to swim to the top of the grass.
11. Cyst: This protects the cercarium so prolonging its lifespan.

The drug of choice in the treatment of fasciolosis is triclabendazole, a member of the benzimidazole family of anthelmintics. The drug works by preventing the polymerisation of the molecule tubulin into the cytoskeletal structures, microtubules. However, resistance of F. hepatica to triclabendazole has already been recorded in Australia[1] and Ireland

references:
http://www.studentxpress.ie/educ/biology/bio3.html
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