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| [[Image:Fasciola hepatica.jpg|thumb|right|150px|''Fasciola hepatica - Wikimedia Commons]] | | [[Image:Fasciola hepatica.jpg|thumb|right|150px|''Fasciola hepatica - Wikimedia Commons]] |
| [[Image:Fasciola hepatica adult.jpg|thumb|right|150px|''Fasciola hepatica'' adults from a horse - Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]] | | [[Image:Fasciola hepatica adult.jpg|thumb|right|150px|''Fasciola hepatica'' adults from a horse - Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]] |
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| For instance, wet summers increase both the number of snail habitats and the hatching of fluke eggs, leading to many infected snails. These in turn shed many cercariae, which form a high density of metacercariae on herbage to increase the risk of fasciolosis. Conversely, in dry summers, fewer fluke eggs hatch and snails are restricted to their permanent habitats. Fewer snails become infected and cercariae and metacercariae numbers are low and confined to the areas where snails can survive. The risk of fasciolosis is therefore reduced. | | For instance, wet summers increase both the number of snail habitats and the hatching of fluke eggs, leading to many infected snails. These in turn shed many cercariae, which form a high density of metacercariae on herbage to increase the risk of fasciolosis. Conversely, in dry summers, fewer fluke eggs hatch and snails are restricted to their permanent habitats. Fewer snails become infected and cercariae and metacercariae numbers are low and confined to the areas where snails can survive. The risk of fasciolosis is therefore reduced. |
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− | | + | A slightly larger trematode, ''F. gigantica'', causes a similar condition in tropical regions. |
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− | *Large numbers of metacercariae ingested over a short period of time leads to acute diseasegnosis
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− | *Smaller numbers ingested over a longer period of time leads to chronic disease
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− | *'''Feed intake'''
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− | **Fluke infections cause reduced food intake
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− | NOTE: chronic fasciolosis occurs at a time of year when animals are on a low plane of nutrition. This combined with the reduced food
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− | intake causes a significant effect on the development and severity of clinical and subclinical fasciolosis.
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− | *'''Species susceptibility'''
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− | **The proportion of flukes that reach the bile ducts is determined mainly by
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− | ***The fibroplastic potential of the liver
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− | ***The effectiveness of the protective immune responses (which are ineffective in sheep)
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− | **Therefore, establishment rate is sheep>cattle>pig
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− | A similar but slightly larger species, ''F. gigantica'', occurs in wetter tropical regions. | |
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| ==Signalment== | | ==Signalment== |