Wild parsnip (Pastinaca sativa)-induced photosensitization in goats and horses

Authors: Stegelmeier, Bryan; Colegate, Steven; Knoppel, Edward; LEMOS, DANILO - Federal University Of Campina Grande; ROOD, KERRY - Utah State University; COLLETT, MARK - Massey University

Submitted to: International Symposium on Poisonous Plants
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2015
Publication Date: 6/5/2015
Citation: Stegelmeier, B.L., Colegate, S.M., Knoppel, E.L., Lemos, D., Rood, K.A., Collett, M.G. 2015. Wild parsnip (Pastinaca sativa)-induced photosensitization in goats and horses. International Symposium on Poisonous Plants. 9:48-53.

Interpretive Summary: Wild parsnip (Pastinaca sativa is a European weed that was inadvertently introduced and has subsequently spread through many parts of North America. It has also been sporadically associated with photosensitization (sun burn) of livestock and humans. Several toxins have been identified in wild parsnip, but little is known concerning the importance of exposure route (if dermal exposure, ingestion, or both produce clinical disease), why some species are more susceptible, or if there are species-specific toxin metabolites. The objectives of this study were to confirm the presence of furanocoumarins in locally-collected P. sativa, describe clinical P. sativa photosensitization in horses, and better characterize the histologic and immune response to both oral and transdermal P. sativa phototoxicity in goats and a horse. These findings suggest that horses are more sensitive to P. sativa-associated contact photodermatitis than goats. Hypersensitivity does not appear to be a component of P. sativa photosensitivity. Additionally, since the goats exposed to dietary P. sativa were only mildly affected, and cattle were unaffected in the field case, it may be that ruminants are less susceptible to ingested P. sativa-induced photosensitization. More studies are needed to better define species-specific metabolism and toxicokinetics. Comparative toxicokinetics and rumen metabolism studies are underway to better define these differences.

Technical Abstract: Wild parsnip (Pastinaca sativa is a European biennial weed that was inadvertently introduced and has subsequently spread through many parts of North America. Though it is generally considered a nuisance as it displaces beneficial forages. It has also been sporadically associated with photosensitization of livestock and humans. Several photodynamic furanocoumarins have been identified in P. sativa. These furanocoumarins have also been identified in other plants that produce photosensitivity, but little is known concerning the importance of exposure route (if dermal exposure, ingestion, or both produce clinical disease), why some species are more susceptible, or if there are species-specific toxicokinetics. Some lesions in humans develop in locations that are not exposed to direct sunlight and the lesions can resemble urishiol-induced allergic dermatitis. Plant and synthetic furanocoumarins have been shown to produce photoallergic contact dermatitis. No work has been done to determine if an allergic reaction contributes to P. sativa and other plant furanocoumarin-induced photosensitivity. The objectives of this study were to confirm the presence of furanocoumarins in locally-collected P. sativa, describe clinical P. sativa photosensitization in horses, and better characterize the histologic and immune response to both oral and transdermal P. sativa phototoxicity in goats and a horse. These findings suggest that horses are more sensitive to P. sativa-associated contact photodermatitis than goats. Hypersensitivity does not appear to be a component of P. sativa photosensitivity. Additionally, since the goats exposed to dietary P. sativa were only mildly affected, and cattle were unaffected in the field case, it may be that ruminants are less susceptible to ingested P. sativa-induced photosensitization. More studies are needed to better define species-specific metabolism and toxicokinetics. Comparative toxicokinetics and rumen metabolism studies are underway to better define these differences.