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234 bytes added ,  11:19, 10 August 2010
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{{unfinished}}
 
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{{cow}}
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*'sunburn-like' lesions
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*cattle and sheep
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==Description==
*sharply confined to the unpigmented areas of the skin
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Photosensitisation is a condition of the dermis caused by a reaction induced by photodynamic agents (PDAs) exposed to UV light in the skin of animals that have eaten certain plants. Photosenstisation is primarily a condition of sheep, cattle and horses but other species may also be susceptible.
*occurs as a result of the effect of strong sunlight
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Photosensitisation can be divided into two categories; primary and secondary photosensitisation). Primary photosensitisation occurs due to the normal ingestion of growing lush green plants containing PDAs. Secondary (hepatogenous) photosensitisation occurs as a result of liver or bile duct damagem, leading to accumulation of phylloerythrin in the blood, body tissues and skin due to insufficient conjugation and excretion by the liver.
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==Clinical signs==
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The condition is characterised by 'sunburn-like' lesions that are confined to unpigmented areas of the skin
 
**due to the effect of UV light on a photodynamic agent (PDA) present in the skin, such as is '''phylloerythrin''' derived from chlorophyll
 
**due to the effect of UV light on a photodynamic agent (PDA) present in the skin, such as is '''phylloerythrin''' derived from chlorophyll
 
**therefore, the disease occurs mostly in those animals consuming large quantities of grass
 
**therefore, the disease occurs mostly in those animals consuming large quantities of grass
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**corticosteroid induced
 
**corticosteroid induced
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===Primary photosensitisation===
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====Causes====
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*normal ingestion of growing lush green plants containing PDA
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**plants containing such fluorescent pigments
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***''Hypericum perforatum'' (St John's Wort) - active principle is hypercin
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***''Lolium perenne'' (Perennial Rye Grass) - active principle is perloline
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*drugs
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**phenothiazine
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**thiazides
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**tetracyclines
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**sulphonamides
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*inherited porphyria
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===Secondary photosensitisation===
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*photosensitisation secondary to liver damage
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====Cause====
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*hepatogenous photosensitisation
 
*hepatogenous photosensitisation
 
**chlorophyll is metabolised to '''phylloerythrin'''
 
**chlorophyll is metabolised to '''phylloerythrin'''
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