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Photosensitisation (view source)

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==Description==

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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.

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Photosensitisation is a condition of the dermis caused by a reaction induced by photodynamic agents 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.

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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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The condition can be divided into two categories; primary and secondary photosensitisation. Primary photosensitisation occurs due to the normal ingestion of lush green plants containing photodynamic agents. Secondary (hepatogenous) photosensitisation occurs as a result of liver or bile duct damage, leading to accumulation of phylloerythrin in the blood, body tissues and skin due to insufficient conjugation and excretion by the liver.

==Clinical signs==

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.

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==Diagnosis==

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**therefore, the disease occurs mostly in those animals consuming large quantities of grass

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**the UV light is changed to a longer wavelength which produces the necrosis of the skin

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*many unknown/poorly understood causes

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**feeding rape, kale, lucerne, alfalfa

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**mouldy hay

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**lush pasture

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**corticosteroid induced

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*hepatogenous photosensitisation

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**chlorophyll is metabolised to '''phylloerythrin'''

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**when the liver or bile ducts are malfunctioning (eg hepatitis or bile duct obstruction) due to severe toxic damage, '''phylloerythrin''' escapes into the circulation and settles in the tissues including the skin

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**the pigment accumulates causing photosensitisation

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*hepatotoxic plants

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**''Senecio jacobea'' (Ragwort)

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**''Lantana camara'' (Lantana)

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**''Lupinus angustifolius'' (Lupins)

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**Blue-green algae

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===~~Microscopically~~===

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*subepidermal vesicles

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**ulcerate

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**become secondarily infected

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~~===Treatment===~~

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*remove from sunlight

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~~===Protosensitising Agents===~~

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*Phenothiazine which was used as an anthelmintic

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*Tetracycline - if one injects bitches with tetracycline when pregnant, puppies are born with brown [[Oral Cavity - Teeth & Gingiva - Anatomy & Physiology|teeth]], which fluoresce under UV light.

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*Haemosiderin may also produce pinky / brown colour to [[Oral Cavity - Teeth & Gingiva - Anatomy & Physiology|teeth]] usually due to damage and haemorrhage into [[Oral Cavity - Teeth & Gingiva - Anatomy & Physiology|tooth]].

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==Treatment==

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Affected animals should only be allowed access to grazing at night. If the animal is affected by secondary photosensitisation, a low-protein, high-energy diet is recommended such as beet pulp.

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==Prognosis==

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In general the prognosis is favourable for primary photosensitisation and poor for secondary photosensitisation.

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Signarski

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