Tribulus terrestris

Abstract

DISTRIBUTION: It is found as a weed, widely distributed in disturbed places, old lands, overgrazed areas and along stream banks especially in dry, hot regions.

BOTANICAL DESCRIPTION: General: A perennial, flat-growing, creeper with an underground root system from which a number of branches develop annually, spreading around to cover the soil. Leaves: The leaves are compound with 5 - 8 pairs of leaflets. These are even woolly when young. Flowers: The small yellow flowers are borne in the axils of the leaves. Fruit: Woody fruit with strong, sharp, conical, spiny growths.

TOXIC PRINCIPLE: • Plants rarely toxic - often regarded as good food in the Karoo. • During outbreaks certain camps are toxic. • Latent period 2-5 days. (Latent period for facial eczema is 10-14 days) Toxic principle: Steroidal saponins.

MECHANISM OF ACTION: • Hydrolysis of a steroidal saponin to diosgenin with subsequent hydrogenation, reduction and epimerisation which occurs in the rumen. • Epismilagenin and episarsasapogenin, amongst others, are formed, absorbed and conjugated with glucuronic acid in the liver to be excreted via the bile. • However, the epismilagenin and episarsasapogenin glucuronides bind to Ca2+ to form an insoluble salt which precipitates to form biliary crystals which obstruct the bile ducts.

SYNDROMES: Geeldikkop Obstruction of biliary system.

SYSTEMS AFFECTED: Liver.

CLINICAL SIGNS: • Signs are typical of secondary photosensitivity - swollen head, - exudation, - sloughing of skin and - coronitis. • Severe icterus. • Problem of no shade in the Karoo. • Sheep stand in the shade of fence poles and bushes, or even other sheep’s shadow.

DIAGNOSIS: • History • Area • Wilted dubbeltjies • Signs in large numbers for definitive diagnosis • Histopathology of especially liver and kidney.

NECROPSY: Macroscopical findings: • Icterus and photodermatitis. • Liver: Slight hepatomegally and discoloured, khaki to yellow - brown. • Chalky white sediment in bile ducts and gall bladder. • Liver morphology never distorted as in F.E. (facial eczema). • Kidneys: Swollen and light in colour, with small green foci distributed through cortex.

HISTOPATHOLOGY: • Accumulation of crystalloid sediment in bile ducts leading to partial or complete occlusion and concentric, lammellar periductal fibrosis. • The crystalloid material washes out and clefts remain. • Plate-like structures seen on scanning EM.

TREATMENT: 1. Keep in shade 2. Diet low in chlorophyll 3. Valuable animals - barrier creams and tattoo ink will protect from sunburn. 4. Antihistamines, corticosteroids, cholagogues, liver supportive treatment. Problems: • numbers, • extensive nature of farming, • Karoo sun.