Phalaris species

Abstract

DISTRIBUTION: • Originally from the Mediterranean regions, it is an introduced species to South Africa, where it has escaped from cultivated pastures. • Grows in disturbed places, seldom in the veld.

BOTANICAL DESCRIPTION: General: A sparse annual tufted grass. Leaves: The hairless leaf blade is flat and firm. Inflorescence: A dense light green to almost white spike-like panicle. 3-Flowered flat awnless spikelets are papery and striped. Conspicuous white membranous ligule. Flowers from September - January.

TOXIC PRINCIPLE: • Serotonin-like tryptamine alkaloids • Structurally similar to serotonin • Functions similarly to serotonin and catecholamines in nervous systems.

SYNDROMES: Phalaris staggers.

SYSTEMS AFFECTED: Central nervous system.

CLINICAL SIGNS: Cardiac syndrome: • Sudden collapse when excited • Respiratory distress and cyanosis • Arrhythmia, tachycardia, ventricular fibrillation and cardiac arrest Nervous syndrome (Phalaris staggers in sheep): Acute poisoning: • Transient signs (functional problem) Chronic poisoning: • Slow, progressive, irreversible, fatal neurological condition • Nervous excitation - precipitated by exercise (typical) • Hyperexcitability • Generalised tremors • Incoordination, limb movement stiff, inability to bend hocks - dragging of hind legs. • Even tetanic convulsions. • May die or recover and walk away apparently unaffected • If left on pasture condition worsens • Animal becomes recumbent and show repeated clonic convulsion until death occurs • Mortalities may even occur up to 1 week after removal • Clinical signs may persist for 2 months (elicited by exercise). Cattle: Usually mild signs: Stiffness of hocks and dragging of toes.

NECROPSY: Acute cardiac syndrome: Signs of cardiac failure. Chronically affected animals: • Green-grey to blue discoloration of brain, spinal cord, renal medulla and liver. • Leaches into formalin after few weeks. • Intracytoplasmic yellow brown granular pigmentation in neurons of brain and spinal cord. • Degeneration and necrosis of affected neurons.

TREATMENT: • No preventative measures for cardiac form. • Nervous form (Phalaris staggers) prevented by cobalt per os. • Dosing weekly (28 mg/sheep). • Heavy Co-bolusses. Co on pasture. (Parenteral Co or Vit. B12 ineffective).