Abstract
Erodium moschatum is an exotic weed in the southern and southwestern coastal areas of the Western Cape Province (WCP), South Africa. It has been suspected as the cause of photosensitivity in sheep. However, attempts to induce photosensitivity by dosing it to sheep have thus far been unsuccessful. During August 1999, 2 sheep suffering from severe photosensitivity were presented for clinical examination to the Western Cape Provincial Veterinary Laboratory (WCPVL). One sheep was sacrificed for autopsy. Except for skin lesions associated with photosensitivity, no icterus or other lesions were present. Histopathological examination of affected skin revealed epidermal necrosis while the liver had no microscopic lesions. It was therefore concluded that the sheep might have been suffering from primary photosensitivity. The farm from which the sheep came, situated in the Malmesbury district, WCP, was visited to determine the source of the photodynamic agent. The flock from which the sheep originated had been grazing in a camp where E. moschatum was growing abundantly and had been heavily grazed. Some remaining Erodium in the camp was collected, pulped and dosed over a period of 7 days to an adult sheep. Another sheep was dosed simultaneously with Erodium growing on the premises of the WCPVL. Both sheep developed mild photosensitivity, which was confirmed by histopathological examination of skin biopsies. It was concluded that E. moschatum can induce photosensitivity (probably the primary type) in sheep if ingested in large quantities.
Highlights
Animals are considered photosensitive if they develop dermatitis of unpigmented skin that is not protected by fleece or hair coat when exposed to sufficient solar radiation[10]
This paper describes a natural outbreak of photosensitivity in a flock of sheep, which was attributed to the ingestion of E. moschatum, and confirmation of its toxicity in a dosing trial
EXPERIMENTAL PHOTOSENSITISATION The remainder of the fresh plant material was pulped in a blender and dosed orally with a stomach tube over a period of 5 days to an adult sheep (Sheep 3) from a flock of 70 unshorn South African Mutton Merinos grazing on the premises of the Western Cape Provincial Veterinary Laboratory (WCPVL) at Stellenbosch
Summary
Animals are considered photosensitive if they develop dermatitis of unpigmented skin that is not protected by fleece or hair coat when exposed to sufficient solar radiation[10]. Photodynamic agents ( known as phototoxins) can occur naturally in certain plants, inducing photosensitivity when these plants are ingested or come into contact with unproaWestern Cape Provincial Veterinary Laboratory, Private Bag X5020, Stellenbosch, 7599 South Africa. In South Africa the plant Hypericum perforatum (St John’s wort), which is notorious for causing primary photosensitivity, occurs abundantly at certain localities in the Western Cape Province[1], but has never been implicated in local outbreaks of photosensitivity[4].
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