Plants of the Urtica genus are found around the world. There are estimated to be around 100 species of nettle, with only 2 reported in Western Australia, Urtica urens (small nettle) and the less common Urtica incisa (scrub nettle). The giant nettle Urtica dioica is commonly found in many regions, most commonly in Australia in the south east. Nettles do have benefit and are used in cooking and making teas in many countries. Control is difficult; see this excerpt from Gardening Australia.
The ‘urticating’ hairs or trichomes of the stinging nettle contain a number of compounds that can cause pain and irritation upon contact with the skin. These include the pro-inflammatory substances histamine, acetylcholine, formic acid and serotonin. These hairs are likened to little hypodermic needles, waiting to inject their contents onto and into the skin of unsuspecting humans and animals. The nettle sting can even survive plant drying for literally hundreds of years. The term ‘urticaria’ describes itchy, raised welts and is derived from the effects of the plant genus Urtica on skin.
Identification: One of the most common species is Urtica dioica. These perennial plants tend to have long, heart-shaped leaves that grow opposite each other on long stems. The stems can reach 0.5 metres in height. Both the stems and the upper and lower surface of the leaves are covered in ‘urticating’ hairs. They have small fuzzy white flowers. Plants that look similar include horse balms, help nettles and white snakeroot.
Horse effects
Horses that are ‘stung’ by nettle can vary in signs, from mild irritation through manic behaviour. Horses at the latter end of the pain spectrum may benefit from sedation. Exposed areas readily develop hives and welts that are typically very itchy. The signs can persist for 24-48 hours.
Treatment is symptomatic and usually involve a combination of intravenous corticosteroids (eg, dexamethasone) and anti-histamines. Washing the area with cold water can provide relief. Once settled, anti-inflammatory creams, such as hydrocortisone may also help.
Tags: Toxicology; Dermatology