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| | In some cases, sub-acute fasciolosis may occur if infections has occured over a prolonged period. In these instances, disease is caused by both adult flukes and larvae and ill thrift, lethargy, dyspnoea is seen from around December to March. | | In some cases, sub-acute fasciolosis may occur if infections has occured over a prolonged period. In these instances, disease is caused by both adult flukes and larvae and ill thrift, lethargy, dyspnoea is seen from around December to March. |
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| − | '''Sub-clinical effects''' | + | In addition to these presentations, ''[[Fasciola heptatica]]'' has subclinical effects on sheep. Fleece weight and fibre quality are affected by even small fluke burdens, and there is some evidence that lambing percentage and lamb growth rates may be negatively influenced. Condemnation of affected livers at slaughter also causes economic losses. |
| − | *In sheep, fleece weight and fibre quality are affected even by small fluke burdens. There is some evidence that reproductive performance (number of lambs born and growth-rate of lambs) is inversely influenced, but this has not been well documented.
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| | *Liver condemnations cause economic losses at slaughter | | *Liver condemnations cause economic losses at slaughter |
| | *Longer finishing times to slaughter weight and reduced carcass value in beef cattle | | *Longer finishing times to slaughter weight and reduced carcass value in beef cattle |
| | *Reduced milk yield and quality in dairy cows | | *Reduced milk yield and quality in dairy cows |
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| − | Metacercariae excyst → immature flukes present in the small intestine → migrate across the peritoneal cavity (about 1 week) → to the liver → migrate through the liver parenchyma for 6-7 weeks becoming more destructive as they grow → enter bile ducts
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| − | *The prepatent period is 10-12 weeks
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| − | ====Acute Fascioliasis====
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| − | The acute disease is a less common type of Fasciola hepatica, and generally occurs 2-6 weeks after large ingestion of metacercariae. The young liver flukes migrate through the liver parenchyma causing severe haemorrhaging, due to the damage to the [[Liver - Anatomy & Physiology|liver]] vasculature.
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| − | This occurs in late autumn and winter, mainly between the months of August to October. Outbreaks of acute fascioliasis usually present as sudden deaths. On examination infected animals are weak, with pale mucous membranes. They may also have enlarged livers, and the liver surface may be cover with a fibrinous peritonitis, particularly evident on the ventral lobe. Tracts become filled with blood and degenerate hepatocytes later infiltrated with [[Eosinophils|eosinophils]], [[Lymphocytes|lymphocytes]] and replaced by fibrosis.
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| − | [[Image:Fasciola hepatica - bile duct.jpg|300px|thumb|right|'''Fasciola hepatica (Copyright Flukeman, Wikimedia Commons) ''']]
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| − | ====Subactute Fascioliasis====
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| − | This is caused by ingestion of metacercariae over a longer period of time. Some may have migrated to the bile ducts, causing [[cholangitis]], whilst other metacercariae are migrating through the liver causing lesions similar to those present in acute fascioliasis. The infected host may present with severe haemorrhagic anaemia, with [[hypoalbuminaemia]], rapid loss of body condition, reduced appetite, pale mucous membranes, and submandibular oedema may also be present. On post-mortem, an enlarged liver is common and haemorrhagic tracts are usually visible on the liver surface. If left untreated, it is often fatal. This form of fascioliasis occurs around 6-10 weeks after ingestion of the metacercariae by the host, and like acute fascioliasis occurs in late autumn and winter.
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| − | ====Chronic Fascioliasis====
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| − | This is usually seen in late winter, early spring and is currently the most common fascoloiasis seen. It occurs around 4-5 months after ingestion of the metacercariae. Hypochromic and macrocytic anaemia and hypoalbuminaemia are common, as the adult flukes are capable of sucking up to 0.5ml of blood each day. In heavy infections, this can prove to be a severe loss.
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| − | Infected animals may present with progressive loss of body condtion, reduced appeptite, which along with hypoalbuminaemia can result in an gaunt animal. Other common signs include pale mucous membranes, and submandibular oedema, more commonly known as 'bottle jaw.' On biopsy the liver will have an irregular shape, distorted shape with areas of fibrous tissue replacing the cells damaged by the migrating flukes. The bile ducts appear dilated, and dark, and it is often possible to express numerous numbers of adult flukes from within the ducts. Pathology is similar in both sheep and cattle, expect in cattle you may see calcification of the bile ducts, and enlargement of the gall bladder. The calcified bile ducts are often seen protruding from the liver surface, which is known as 'pipe stem liver.'
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| | ===Laboratory Tests=== | | ===Laboratory Tests=== |