Photosensitisation

Description

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. 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.

Treatment

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.

Prognosis

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

References

• Gupta, R. C., (2007) Veterinary Toxicology: basic and clinical principles Academic Press'
• Haskell, S. R. R., (2008) Blackwell's five-minute veterinary consult: ruminant John Wiley & Sons
• Lavoie, J. P., (2009) Blackwell's five-minute veterinary consult: equine John Wiley & Sons