There is none, esp. where there is a permanent source of water.
The life cycle moves from the ruminant to a snail which then sheds the next life stage onto the grass which is then consumed by the ruminant again.
The parasite ends up in the liver and causes severe damage there as it migrates through the bile ducts. This is often detected only once livers are condemned at the abattoirs regularly.
Any damage caused by the parasite, even after treatment, is usually permanent.
Include weight loss, anaemia, abdominal distension, death. Deterioration is generally gradual, allowing time for a diagnosis and treatment. Generally younger animals are worse off than adults.
This is obtained from stool samples where worm eggs can be seen under the microscope, clinical examinations and post mortems.
There is very little resistance to drugs used for liver fluke; just check the packaging for efficacy.