Most areas of Scotland have witnessed increased amounts of rainfall over the past few months so it comes as no surprise that the risk of Liver Fluke will also be higher. In this article, the National Animal Disease Information Service (NADIS) outlines the clinical signs and economic implications of this debilitating disease which can result in death if not treated.

Liver Fluke (Fasciolosis) – Scotland

Fasciola hepatica infects the liver of both cattle and sheep. For part of its life cycle, liver flukes inhabit the snail, Limnea truncatula. This important stage of the parasite life cycle necessitates wet and warm conditions (above 7-10°C).

Economic implications

• Acute fluke may kill up to 10% of sheep at-risk causing significant financial loss

• Sub-acute fluke – marked by a reduction in scanning percentage (approximately 25% lower), high barren rate (approximately 10-20%) – when infection occurs around mating

• Chronic fluke – Severe condition loss, high mortality if untreated

Clinical signs

Liver fluke causes three types of disease:

• Acute – autumn

• Sub-acute – autumn

• Chronic – winter

Acute fasciolosis

• August to October

• Sheep die suddenly from haemorrhage and liver damage

• Others in the group reveal lethargy and reduced grazing activity

• Gathering may prove difficult because sheep are reluctant to run because of pain

Diagnosis

Other causes of sudden death your vet will consider include:

• Clostridial disease; pulpy kidney, blackleg, Black disease, braxy in unvaccinated stock

• Tick diseases as habitats often similar for both snails and ticks – Louping ill

• Pasteurellosis or other septicaemic diseases

Subacute fasciolosis

• Rapid loss of body condition

• Poor fleece quality despite adequate flock nutrition

• Depression

• Inappetence

• Weakness and may be unable to stand

• Poor fertility – high barren rate, low scanning percentages

Diagnosis

Acute/subacute fasciolosis

• Veterinary investigation of blood samples reveals raised liver enzymes

• Immature flukes are demonstrated in the bile ducts and gall bladder at necropsy

Chronic fasciolosis

• Very poor body condition score

• Poor fleece quality

• May show ‘bottle jaw’

• Die in an emaciated state.

Poor condition affecting many of your sheep may also result from:

• Inadequate flock nutrition

• Chronic parasitism including anthelmintic-resistant strains

• Virulent foot rot

• Johne’s disease

• Poor dentition especially cheek teeth

Treatment

• Triclabendazole is highly effective at killing all stages of flukes responsible for acute fasciolosis. Drenched sheep should be moved to clean pasture. Re-treatments of sheep every three weeks or so during a high-risk period on contaminated pasture is unsustainable and resistance to triclabendazole is now commonly suspected. A more sustainable control programme should be developed with your veterinary surgeon.

• Closantel, nitroxynil and oxyclosanide are not effective against very young liver flukes and should be used in the treatment of subacute and chronic fasciolosis. Once again, treated sheep must be moved to clean pastures.

• Improved nutrition is essential.

Management/Prevention/Control measures

• Fluke infestations are controlled by strategic drenching based upon advice written in the veterinary flock health plan. During low risk years triclabendazole is administered in advance of the predicted challenge during October, with another flukicide drug (possibly closantel) administered in January and another drug in May.

• In years when epidemiological data indicate a high risk of fasciolosis such as 2015, an earlier triclabendazole treatment may be necessary in September. While it may be possible to eradicate fluke from a property, there are considerable risks from not drenching as the appearance of clinical disease in a few sheep represents serious losses in the whole flock. In certain areas wildlife hosts may play an important role in the disease dynamics.

• Fencing off snail habitats is rarely practicable and in most situations is cost prohibitive as these are often extensive sheep enterprises. Drainage is cost prohibitive and many properties are subject to environmental controls.