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| Fasciolosis is a condition of ruminants which causes significant economic losses through death, subclinical and clinical disease. The causative organism is the trematode ''[[Fasciola hepatica]]'' which primarily parasitises the bile ducts of sheep and cattle but may occasionally be found in the horse. ''Lymnaea truncatula'', a mud snail, is the intermediate host of ''[[Fasciola hepatica]]'', and transmission of disease is dependent on the presence of appropriate snail habitats. These habitats are more plentiful in areas of high rainfall, such as the western British Isles. However, infected animals may be found outwith these areas due to the transportation of livestock. The association of fasciolosis with wetter habitats lends a seasonal nature to disease outbreaks, and can help predict the severity of these. | | Fasciolosis is a condition of ruminants which causes significant economic losses through death, subclinical and clinical disease. The causative organism is the trematode ''[[Fasciola hepatica]]'' which primarily parasitises the bile ducts of sheep and cattle but may occasionally be found in the horse. ''Lymnaea truncatula'', a mud snail, is the intermediate host of ''[[Fasciola hepatica]]'', and transmission of disease is dependent on the presence of appropriate snail habitats. These habitats are more plentiful in areas of high rainfall, such as the western British Isles. However, infected animals may be found outwith these areas due to the transportation of livestock. The association of fasciolosis with wetter habitats lends a seasonal nature to disease outbreaks, and can help predict the severity of these. |
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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. |
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− | | + | *Large numbers of metacercariae ingested over a short period of time leads to acute diseasegnosis |
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− | === Geographical distribution of disease ===
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− | Transmission is dependent on the snail, and therefore associated with snail habitats.
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− | === Weather patterns and disease risk ===
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− | '''Wet summer'''
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− | Many fluke and snail eggs hatching and snail habitats expanded, therefore:
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− | → snail population increases rapidly
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− | → many infected snails
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− | → many cercariae shed
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− | → high density of metacercariae on herbage
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− | → '''increased''' risk of disease
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− | '''Dry summer'''
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− | Few fluke and snail eggs hatching and snails restricted to permanent habitats, therefore:
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− | → snail populations small and overcrowded
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− | → few infected snails, high mortality
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− | → few cercariae shed
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− | → few metacercariae confined to restricted areas
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− | → '''reduced''' risk of disease
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− | *Large numbers of metacercariae ingested over a short period of time leads to acute diseasegnosis== | |
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