Understanding Liver Fluke in Sheep Flocks
Liver fluke disease Liver fluke disease (fasciolosis) can occur in three forms:
1. ACUTE DISEASE Acute fasciolosis can occur in sheep 2-6 weeks after large numbers of metacercariae are ingested over a short period of time. The large numbers of parasites which then emerge in the intestine and travel to the liver cause severe damage. Signs: • Sudden death, with/without prior warning • Weakness, abdominal pain and reluctance to move • Jaundice (yellowing of the mucous membranes and whites of the eyes) • Anaemia due to internal blood loss (pale membranes) Timely treatment with a product effective against early immature fluke (flukicide containing triclabendazole [TCBZ]) is crucial to combat acute disease outbreaks. Occasionally animals fail to respond to treatment, either due to anthelmintic resistance or because the livers (which are damaged by the invading fluke) are no longer able to convert the TCBZ to its active form. In these cases, alternative treatments (which do not require conversion by the liver to an active form) must be used. However, TCBZ is the only ingredient approved for treating early immature fluke.
2. SUBACUTE DISEASE Subacute fasciolosis occurs when a smaller number of metacercariae are ingested, or ingestion takes place over a longer period of time. However, the migration of the parasites still causes significant internal damage to the animal as the infection progresses. Signs: • Rapid weight loss • Lethargy • Anaemia (pale membranes) • Sometimes death Sub-acute infections are often caused by a mix of immature and late immature stages occurring at the same time as adult parasites in the same animal, and treatment with a suitable flukicide covering both adult and immature fluke is required (See Table 2).
3. CHRONIC DISEASE Chronic fasciolosis occurs in animals that have had an untreated liver fluke infection for some time. Signs: • Progressive, sometimes extreme weight loss • Submandibular and/or ventral oedema (bottle-jaw and swollen stomach) • Diarrhoea • Anaemia (pale membranes) Treatment with a flukicide effective against adult parasites is needed (See Table 2).
These signs can also arise due to a number of other conditions, so speak to your veterinary practitioner before making treatment decisions.
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