Hypericum perforatum (perforated
St John's wort, common St John's wort, millepertuis). Related species: H. crispum,
H. calycinum (rose of Sharon, St John's
wort). A member of the plant family HYPERICACEAE. Herbaceous
plant with dense foliage; the leaves and stems contain small secretory glands which
produce a translucent chlorophyll-free oil with a balsamic odour. The plant has large
conspicuous, cup-shaped yellow flowers with prominent stamens; the fruit are ovoid
capsules containing black seeds.
Animals most affected
Sheep (cattle, horses).
Ingestion through grazing or consumption
of fresh cuttings or contaminated hay or fodder.
Contains hypericine, a red fluorescent pigment responsible for causing primary photosensitization
in animals. The entire plant is toxic, particularly the flowers. Drying the plant
does not modify significantly its toxicity. Toxic doses not known.
There is a latent period between ingestion of the plant and manifestation of clinical
signs, varying from several hours to several days. The effects occur exclusively
when the animal is exposed to sunlight.
anorexia, restlessness, prostration, occasionally convulsions.
constipation or mild diarrhoea;
late onset (from several hours to 1-3
days) of photodermatitis in fine, unpigmented skin causing a red blotchy discoloration
(like red wine sediment), severe pruritus, oedema with serous exudate and formation
of black sticky scabs resulting in hard cracked skin;
affected animals become very sensitive
to touch, with hyperirritability, and extreme hyperaesthesia;
possibility of stomatitis, keratitis,
kerato-conjunctivitis, opacity of the cornea, risk of secondary infection, necrosis
in and gangrene of cutaneous tissue;
if treatment is given, mortality is rare.
principally cutaneous: exudative dermatitis;
degeneration of the liver, inflammation
of the gall bladder.
No antidote. Symptomatic and supportive care
place animal in shade for several days;
treat cutaneous sores with topical antiseptics
administer desensitizing drugs (to reduce
hyperallergenicity) and pain killers;
nicotmamide (factor PP);
antihistamines appear to be ineffective.