Liver Fluke disease is at an all time high, this is mainly due to higher water levels in the pastures and milder weather conditions which have allowed the pond snail to thrive. It is important to recognise that liver fluke differs from roundworms in several respects. Firstly, the life-cycle is longer, taking a minimum of 18-20 weeks. Secondly, there is a multiplication phase in the snail resulting in around 500-600 stages (cercariae) being shed onto pasture for each stage that enters the snail. These stages encyst on vegetation as metacercariae and are infective for livestock for several months. Thirdly, flukes can accumulate in the liver as they induce little immune response in the host.
Types of fluke disease and treatment:
Fluke disease occurs in three forms, acute, sub-acute and chronic, the latter being the most common.
Acute. – This occurs when massive numbers of infective cysts are ingested from herbage over a short period. Acute infections can lead to sudden deaths in autumn/early winter before fluke eggs appear. Treat sheep immediately, move treated livestock to a well-drained pasture. Treat animals which remain on infected pasture every 3 weeks.
Sub-acute. – Cysts are ingested over a longer period and the liver contains immature and some adult flukes. Disease occurs in late autumn/winter. Treat as for acute disease.
Chronic. – This is associated with a prolonged intake of moderate numbers of infective cysts and the accumulation of adult fluke in the bile ducts. Chronic disease is mainly seen in late winter/early spring and is exacerbated by poor nutrition. A single treatment with any flukicide which has high efficacy against adult fluke is advocated, combined where practical, with a move to low-risk pasture.
Fluke – Preventitive Treatments:
1). Spring/early summer –
To remove adult fluke burdens which accumulate from the previous year’s infection and thus reduce the deposition of eggs on to pasture. This will reduce the summer infection of snails.
2). Autumn –
To prevent immature fluke migration and development following ingestion of metacercariae and to improve the condition of the ewe.
3). Winter –
To kill adult and immature fluke and to prevent liver damage and ill-thrift.
A typical treatment schedule in an average rainfall season would be:
Dose adult sheep in the spring (late April/ May) with a flukicide which is effective against adult stages e.g. Trodax injection or Ovispec 2.5% drench.
Dose all sheep in autumn (October) with a flukicide which is effective against young immature fluke e.g. Fasinex 5% drench (fluke only) or Combinex sheep drench (fluke and worms).
Dose all sheep in winter (January) with a flukicide which is effective against adult and immature fluke e.g. Fasinex 5% drench or Trodax injection.
Further treatments may be necessary in high risk areas if the season has been very wet. Frequency of treatment will also be influenced by the spectrum of activity of the flukicide.