Production Animal Clinical Toxicology

Plants | Epidemiology | Pathogenesis | Clinical Signs | Clinical Pathology | Necropsy

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Plants

• Tribulus terrestris - cathead, caltrop
• Tribulus micrococcus - yellow vine

Epidemiology

animal factors

• primarily sheep affected

plant/environmental factors

• during droughts when summer storms fall on bare cultivation profuse growth occurs
• generally only plant species available

Pathogenesis

• toxins are the betacarboline alkaloids, harman, norharman
• T. terrestris induces a primary disorder in the dopamine circuits of the nigrostriatal complex
• results in asymmetrically impaired function of the extensor muscles

Clinical Signs

a. tribulus staggers (Coonabarabran staggers) associated with T. terrestris

• signs may develop at least 3 months after initial exposure and can last an average of 8 months
• initially mild paresis in hindquarter develops
• further asymmetry develops with one hindlimb showing more weakness than the other
• when running affected animals move hindquarters sideways
• final stages forelimb weakness develops
• recumbency, death
• is chronic, progressive and irreversible

b. transient tribulus ataxia (Narrabri staggers) associated with T. micrococcus

• signs develop in 3 weeks and persist for another 3-5 weeks
• bilateral paresis and ataxia of hindlimbs develops with limbs moving in lateral arcs
• hind toes are frequently dragged
• knuckle over in hind fetlocks; hocks flexed
• severe cases the hindquarters are dragged along, or the animal becomes recumbent
• forelimb gait may become irregular
• most animals recover

Clinical Pathology

• nonspecific

Necropsy

• generally nonspecific apart from pelvic muscle atrophy in some cases
• specific histopathological changes are not seen