Production Animal Clinical Toxicology

Chemicals | Pathogenesis | Clinical Signs | Clinical Pathology | Necropsy | Diagnosis | Treatment

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Chemicals

Compounds

• carbophenothion
• coumaphos
• diazinon
• dichlorvos
• fenthion
• malathion
• parathion
• trichlorphon

Sources

• used mainly as contact or systemic insecticides

Pathogenesis

• organophosphates are lipid soluble and are readily absorbed by all routes
• generally compounds are rapidly metabolised and excreted so subacute or chronic poisoning due to accumulation does not occur
• metabolism and excretion are complex and are dependent on:
• compound itself
• hepatic microsomes
• age of animal
• health of animal
• organophosphates bind with and phosphorylate cholinesterases
• reversal of the reaction is extremely slow
• the esterase is virtually permanently inhibited
• acetylcholine accumulates at synapses
• depending on site of accumulation clinical signs will mimic muscarinic, nicotinic and CNS actions of acetylcholine, i.e. overstimulation of the parasympathetic and post-ganglionic nerves of the sympathetic nervous system

Clinical Signs

• may occur within minutes to several hours
• initially muscarinic effects are observed
• hypersalivation, lacrimation, sweating
• nasal discharge
• myosis
• brachycardia (occasionally tachycardia)
• dyspnoea, coughing
• vomiting, diarrhoea, abdominal pain
• frequent urination
• nicotinic effects include:
• muscular fasciculation
• tetany, stiff-legged gait
• torticollis in cattle and sheep
• CNS effects
• nervousness and apprehension
• ataxia
• convulsions, coma
• death is usually due to respiratory failure or cardiac arrest and can occur 12-24 hours after onset of signs
• a delayed neurotoxicity may occur, from a slow centripetal degeneration of nerves
• reported in horses
• disturbances in proprioception leading to ataxia
• severe cases, peripheral neuropathy and paralysis

Clinical Pathology

• cholinesterase activity in red cells

Necropsy

• nonspecific

Diagnosis

• history
• clinical pathology

Treatment

• atropine to abolish muscarinic effects
• pralidoxime (PAM) to combine with the bound organophosphate to regenerate the enzyme
• sedatives are contra-indicated