Peer-reviewed veterinary case report
Primary photosensitization in horses associated with ingestion of Malachra fasciata Jacq. (Malvaceae) in the Northeast of Brazil.
- Journal:
- Toxicon : official journal of the International Society on Toxinology
- Year:
- 2026
- Authors:
- Riquelme, Lourdes Fernández et al.
- Affiliation:
- Graduate Program in Animal Science · Brazil
- Species:
- horse
Plain-English summary
In a recent case in Northeastern Brazil, four Quarter Horses developed severe skin problems after grazing on a pasture filled with a plant called Malachra fasciata. These horses showed signs of skin irritation, including hair loss, redness, crusty sores, and intense itching, especially in areas exposed to the sun. A closer examination of their skin revealed serious damage, including ulceration and inflammation. After the horses were moved to a shaded area away from the plant, their condition improved, but the skin issues came back when they were exposed to the plant again. This case is the first documented instance of this plant causing skin problems in horses, highlighting the need for careful management of their grazing areas.
Abstract
Malachra fasciata Jacq. (Malvaceae) is an invasive plant widely found in Northeastern Brazil and has been experimentally demonstrated to cause severe dermatitis in sheep. However, its toxic effects in horses have not previously been documented. This report describes primary photosensitization in four Quarter Horses grazing on a pasture heavily infested with M. fasciata in Paraíba, Brazil. Affected animals developed alopecic, erythematous, crusted, and ulcerated lesions on sun-exposed areas, accompanied by severe pruritus and behavioral signs of distress. Histopathology revealed epidermal ulceration with serocellular crusts, marked hyperkeratosis, keratinocyte necrosis, spongiosis, and an eosinophil-rich dermal infiltrate. All horses improved after removal from the infested pasture and were housed in a shaded environment, but lesions recurred upon re-exposure. This case represents the first confirmed report of primary photosensitization caused by M. fasciata in horses and highlights the clinical significance of this emerging toxic plant in equine management.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/41490913/