Production Animal Clinical Toxicology

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

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Plants

• Pimelea simplex - desert rice flower
• Pimelea trichostachya - flax weed
• Pimelea continua
• Pimelea longifolia - flax leaf rice flower

Epidemiology

animal factors

• field cases generally only seen in cattle

plant/environmental factors

• appear soon after spring, summer rains
• seeds germinate only after soaking for a few days
• grow thickest where there has been fire, soil is disturbed or in depressions
• prefer sandy soils; does not grow on black soils or clays
• green plants are highly unpalatable; dry stalks, fragments and plant dust are accidently ingested and cause toxicity

Pathogenesis

• 2 major toxins, simplexin and huratoxin, related to phorbols
• have general cytotoxic effects possibly mediated through disturbing cellular Ca metabolism
• causes St. George or Marree disease, a chronic right-sided heart failure
• also causes unthriftiness
• pathogenesis uncertain, but may be linked to direct cytotoxic effects on cardiopulmonary function, as well as inducing anaemia
• some authors suggest toxins cause constriction of spiral muscles of pulmonary venules: increase in pulmonary resistance causes right-sided heart failure

Clinical Signs

acute

• severe diarrhoea, death may result

chronic

• diarrhoea heralds onset; may become dysentery
• loss of condition
• coat becomes rough
• animals depressed
• about 3 weeks prominent jugular pulse develops
• ventral oedema progressing from intermandibular space brisket, front legs, umbilicus to udder
• muffled heart sounds; increased respiration
• variable appearance of anaemia
• decreased exercise tolerance
• sudden death may occur during exertion

Clinical Pathology

• normocytic, normochromic anaemia
• no haemolysis
• no compensatory erythropoiesis until PCV less than 13%
• mild hypoproteinaemia
• panleucopaenia
• blood in faeces

Necropsy

• moderate pulmonary congestion
• hydrothorax, marked subcutaneous oedema mainly submandibular, cervical and brisket, variable ascites
• right ventricular dilation; myocardial necrosis may be present
• liver enlarged, deep purple colour
• blood oozes from cut surface
• parenchyma sponge-like
• severely dilated sinusoids
• necrosis may be present

Diagnosis

• history
• clinical signs
• necropsy findings

Treatment

• remove, mild cases slowly recover

Control

• graze sheep only
• grazing management