Production Animal Clinical Toxicology

Plants | Epidemiology | Pathogenesis | Clinical Signs | Clinical Pathology | Necropsy | Diagnosis | Treatment | Control

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Plants

Echium plantagineum - Paterson's curse

Senecio spp. - fireweeds, ragwort

Heliotropium spp. - heliotropes

Crotolaria spp. - rattlepods

Epidemiology

animal factors

• all species can be affected
• pigs more susceptible than cattle/horses, sheep less susceptible
• often need several seasons of exposure before toxicity evident

plant/environmental factors

• prolonged and repeated poor seasons lead to pasture contamination to sufficient levels
• may be only growth present
• plant flush after break in drought
• generally plants are not palatable, although sheep eat Paterson's curse
• may have mixture of species (eg Heliotropium and Echium) in a paddock
• can have toxicity from contaminated hay

Pathogenesis

• compounds become activated in tissues and bind to vital cell components
• results in cellular necrosis and/or inhibition of mitosis
• alkaloid metabolites are hepatotoxic and can affect other epithelia particularly pulmonary and renal
• endothelium can also be affected with vascular damage
• ultimately with chronic exposure death results in chronic hepatic failure
• CNS signs relate to elevated NH3 inducing a hepatic encephalopathy
• in sheep hepatogenous Cu toxicity may result
• decreased Cu excretion in bile
• hepatocyte necrosis leads to Cu being stored in increasing amounts in other hepatocytes
• eventually lysosomal collapse means massive release of Cu into blood that has a direct effect on erythrocyte membranes, resulting in haemolysis

Clinical Signs

sheep - 2 syndromes

(i) hepatic failure (less common)

• illthrift developing into emaciation
• icterus and photosensitisation (rare)

(ii) hepatogenous chronic copper toxicity

• reluctant to move
• jaundice
• anaemia
• Hbaemia, Hburia
• terminal respiratory distress

cattle - weight loss and emaciation

• mild to severe diarrhoea
• rectal prolapse
• occasional icterus and photosensitisation
• CNS signs terminally
• apparent blindness
• circling, aimless wandering
• ataxia

horses - similar signs except that loss of condition may occur suddenly over a week

• terminal CNS signs including a "dummy" syndrome may last only several days
• ventral oedema

Clinical Pathology

• hepatic enzymes, bilirubin
• hepatic biopsy
• Hburia in some sheep

Necropsy

• firm fibrotic livers
• portal hypertension
• ascites
• gall bladder and intestinal oedema
• +/-icterus
• if haemolytic crisis has occurred kidneys may be dark or gunmetal in colour
• histopathology
• hepatic necrosis
• hepatic and renal megalocytosis

Diagnosis

• history
• necropsy
• histopathology

Treatment

• none

Control

• grazing management
• eradication of plants
• biological (insect) control