Fasciola hepatica infection is widespread across eastern New South Wales where the annual mean rainfall is about 600 mm or more. Infected areas include the Tablelands and nearby slopes.
Infection is also found in irrigation areas, where the annual rainfall of around 400 mm is supplemented by regular irrigation.
Infection is endemic on the south-eastern coastal areas, often in combination with stomach flukes (paramphistomes).
The adult flukes in the bile ducts produce eggs which are passed in the faeces (see Figure 1).
The eggs hatch when separated from faecal material in wet areas, under optimal conditions. The first larvae or miracidia released (b) invade the lymnaeid snails in which they develop and multiply as sporocyst, rediae and cercariae (c).
The tadpole-like cercariae leave the snails (d) and swim until they encyst on vegetation, forming metacercariae (e), which are the infective stage of the fluke. The entire cycle of the liver flukes in the snails takes two to three months under favourable conditions in the field.
If the metacercariae are ingested by sheep, cattle or other hosts, including people (f), the metacercariae excyst in the small intestine and the released immature flukes penetrate the intestinal wall into the abdominal cavity.
The young flukes penetrate the liver capsule and migrate through the liver tissue for six to seven weeks before entering the bile ducts to become adult flukes (g).
The flukes reach sexual maturity and commence egg production at eight to ten weeks after infection