Pachystigma species

Abstract

DISTRIBUTION: Frequently found in sunny positions or semi-shade in open grassland and “klipveld” (stony veld) in high-lying areas.

BOTANICAL DESCRIPTION: General: Low-growing, deciduous, perennial dwarf shrubs of about 15 cm high with an extensive underground stem and root system from which short, irregular aerial branches are growing. Leaves: The stalkless leaves with entire margins are decussate and the bases of the leaves are joined on either side of the stem by small, triangular stipules. The leaves of P. pygmaeum are covered with short yellow hairs, but P. thamnus has hairless leaves. Flowers: The dense clusters of flowers are star-shaped, small, yellowish-green. Ovary contains 4-5 locules. October - February. Fruit: The fruit is round like a small tomato, but could also be pear-shaped.

TOXIC PRINCIPLE: • A water-soluble polyamine named pavettamine has been isolated. • It has a delayed effect on the heart. • This toxin is pH-labile and will be destroyed at pH < 2,5. • This could explain why only ruminants are susceptible, (rumen pH = 6,8). Mechanism of action: The toxin inhibits synthesis of new myocardial protein, especially myosin.

SYNDROME: Gousiekte

SYSTEMS AFFECTED: Cardiovascular system.

CLINICAL SIGNS: • After ingestion of a lethal dose of the plants, a characteristic latent period of 6 - 8 weeks of apparent normality follows before the animals suddenly die. • The majority of animals typically drop dead, usually after being frightened, handled or chased, although some may die without any stressful event occurring. • In a few cases congestive heart failure such as weakness, panting, respiratory distress and anasarca, particularly of the head, are present.

NECROPSY: Signs of heart failure • Lung oedema • Hydrothorax • Hydropericardium although some cases may not show any macroscopic changes. Irregular areas of pallor (greyish areas) may be seen, particularly in the endocardium.

HISTOPATHOLOGY: • A multifocal to diffuse subendocardial replacement fibrosis accompanied by a round cell infiltration, predominantly in the apex, left ventricular wall and interventricular septum. • Focal to diffuse degeneration and/or necrosis of myofibres. • Hypertrophy or even atrophy of myocardial fibres.

TREATMENT: No specific treatment, only symptomatic and supportive. Avoid unnecessary stressful situations.