Changes

==Introduction==

==Introduction==

primarily a condition of sheep, cattle and horses but other species may also be susceptible.  

primarily a condition of sheep, cattle and horses but other species may also be susceptible.  

The condition can be divided into two categories; primary and secondary. '''Primary photosensitisation''' occurs due to the ingestion of lush green plants containing photodynamic agents, such as St John's Wort or clover. '''Secondary (hepatogenous) photosensitisation''' is the most commmon type of photosensitivity seen in animals and occurs due to liver or bile duct damage, most often as a result of ingestion of hepatotoxic plants such as [[Ragwort Toxicity|Ragwort]]. The normal conjugation and excretion of phylloerythrin (a breakdown product of chlorophyll) is prevented leading to its accumulation in the blood and body tissues. In the skin this leads to the absorption and release of UV light, resulting in a phototoxic reaction.

The condition can be divided into two categories; primary and secondary. '''Primary photosensitisation''' occurs due to the ingestion of lush green plants containing photodynamic agents, such as St John's Wort or clover. '''Secondary (hepatogenous) photosensitisation''' is the most commmon type of photosensitivity seen in animals and occurs due to liver or bile duct damage, most often as a result of ingestion of hepatotoxic plants such as ''Senecio jacobea'' ([[Ragwort Toxicity|ragwort]]), ''Lantana camara'' (Lantana), ''Lupinus angustifolius'' (Lupins) and [[Blue-Green Algae Toxicity|Blue-green algae]]. The normal conjugation and excretion of phylloerythrin (a breakdown product of chlorophyll) is prevented leading to its accumulation in the blood and body tissues. In the skin this leads to the absorption and release of UV light, resulting in a phototoxic reaction.

==Clinical signs==

==Clinical signs==

[[Image:Cow-_photosensitivity.jpg‎|right|thumb|125px|<small><center>Photosensitisation in a Friesian cow (Image sourced from Wikimedia Commons))</center></small>]]

[[Image:Cow-_photosensitivity.jpg‎|right|thumb|200px|<small><center>Photosensitisation in a Friesian cow (Image sourced from Wikimedia Commons))</center></small>]]

The condition is characterised by clearly demarcated 'sunburn-like' lesions that are confined to unpigmented or hairless areas of the skin. The nose, lips, ears, muzzle and udder are commonly affected areas. In the acute stages, the affected area(s) becomes erythematous and oedematous with exudation and crust formation. Animals may be pruritic or painful. Other clinical signs may include swollen lips or muzzle, tachypnoea, tachycardia, diarrhoea and salivation.

The condition is characterised by clearly demarcated 'sunburn-like' lesions that are confined to unpigmented or hairless areas of the skin. The nose, lips, ears, muzzle and udder are commonly affected areas. In the acute stages, the affected area(s) becomes erythematous and oedematous with exudation and crust formation. Animals may be pruritic or painful. Other clinical signs may include swollen lips or muzzle, tachypnoea, tachycardia, diarrhoea and salivation.

Animals should not be grazed on pasture known to contain photodynamic agents and contaminated hay and grain should also be avoided. In the case of farm livestock, less valuable or older animals may be used to 'pre-graze' affected pastures before other animals are introduced.  

Animals should not be grazed on pasture known to contain photodynamic agents and contaminated hay and grain should also be avoided. In the case of farm livestock, less valuable or older animals may be used to 'pre-graze' affected pastures before other animals are introduced.  

==Test yourself with the Liver Pathology Flashcards==

|flashcards = [[Liver_Flashcards_-_Pathology|Liver Pathology Flashcards]]

[[Liver_Flashcards_-_Pathology|Liver Pathology Flashcards]]

[[Sheep Medicine Q&A 10]]

 

|literature search = [http://www.cabdirect.org/search.html?it=any&q2=photosenzitivity&q1=photosensitivity&calendarInput=yyyy-mm-dd&q4=photosensitization&q3=photosensitisation&occuring1=title&show=all&rowId=1&rowId=2&rowId=3&rowId=4&options1=AND&options2=OR&occuring4=title&options3=OR&options4=OR&occuring3=title&occuring2=title&publishedend=yyyy&la=any&publishedstart=yyyy&fq=sc%3A%22ve%22&y=11&x=55 Photosensitisation publications]

==Literature Search==

 

 

[http://www.cabdirect.org/search.html?it=any&q2=photosenzitivity&q1=photosensitivity&calendarInput=yyyy-mm-dd&q4=photosensitization&q3=photosensitisation&occuring1=title&show=all&rowId=1&rowId=2&rowId=3&rowId=4&options1=AND&options2=OR&occuring4=title&options3=OR&options4=OR&occuring3=title&occuring2=title&publishedend=yyyy&la=any&publishedstart=yyyy&fq=sc%3A%22ve%22&y=11&x=55 Photosensitisation publications]

==References==

==References==

* Merck & Co (2008) '''The Merck Veterinary Manual (Eighth Edition)''' ''Merial''

* Merck & Co (2008) '''The Merck Veterinary Manual (Eighth Edition)''' ''Merial''

* Pascoe, R. R., Knottenbelt, D. C. (1999) '''Manual of Equine Dermatology''' ''Elsevier Health Sciences''

* Pascoe, R. R., Knottenbelt, D. C. (1999) '''Manual of Equine Dermatology''' ''Elsevier Health Sciences''

[[Category:Liver_-_General_Pathology]]

[[Category:Liver_-_General_Pathology]]

[[Category:Expert_Review]]

[[Category:Expert Review]]

[[Category:Dermatological Diseases - Cattle]]

[[Category:Dermatological Diseases - Cattle]]

[[Category:Dermatological Diseases - Sheep]]

[[Category:Dermatological Diseases - Sheep]]