(a) With the aid of an annotated diagram, describe the life cycle of the liver-fluke (Fasciola hepatica). Explain how you will prevent the liver-fluke from ...

(a) Life cycle of the liver-fluke (Fasciola hepatica): An annotated diagram should be drawn as a cycle with arrows linking the stages below. The liver-fluke needs two hosts: the primary host (sheep, cattle, goat) and the intermediate host (a mud/water snail).

• Adult flukes live in the bile ducts/liver of the primary host and lay eggs.
• Eggs pass out with the faeces of the animal onto wet pasture.
• In water, each egg hatches into a ciliated larva called a miracidium.
• The miracidium enters a mud snail (intermediate host) and develops through the sporocyst and redia stages, multiplying.
• These develop into tadpole-like cercariae which leave the snail.
• The cercariae encyst on wet grass as metacercariae (the infective stage).
• A grazing animal swallows the metacercariae, which travel to the liver, grow into adult flukes, and the cycle repeats.

Preventing the fluke from completing its life cycle in the field:

• Drain marshy/water-logged grazing land to destroy the snail habitat.
• Kill the mud snails using molluscicides (for example copper sulphate).
• Avoid grazing animals on wet, low-lying pastures, especially in the early morning.
• Deworm (drench) infected animals regularly and dispose of their dung properly to break the cycle.

(c) Three effects of lice on animal production:

• They suck blood and cause anaemia and loss of condition.
• Their bites cause irritation and restlessness, reducing feeding and growth.
• They damage the skin/hide and transmit diseases, lowering the value of the animal.