Branded “the most dangerous plant in Britain”, hogweed has been making headlines following several news reports of severe dermal reactions in both humans and animals after contact. The plant is rapidly spreading throughout the UK and Ireland, and tends to be found around watersides as well as in grassy areas and open woods.
Heracleum mantegazzianum (giant hogweed) and Heracleum sphondylium (cow parsnip, hogweed, keck), contain psoralens, i.e. phytophotoxins that make the skin extremely sensitive to sunlight. Exposure to ultraviolet light results in cell death and subsequent phototoxic effects. Merely brushing against the plant can lead to significant skin damage.
The VPIS has received a total of 23 enquiries relating to hogweed exposure, of which 16 cases were in dogs and 5 in horses. Common clinical signs reported are oral and skin ulcerations, fluid-filled blisters, erythema oedema and vomiting. Raised liver enzymes have also been reported in horses. Signs can develop rapidly within a few hours and open skin lesions pose the risk of secondary infections.
Treatment following exposure should include washing the area with soap and water, limiting exposure to sunlight, and symptomatic and supportive care. Analgesia and steroidal treatments can be used to relieve irritation as required.