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Introduction

  • Discussion focus: Top 10 toxins of 2023, specifically insecticides (ranked #9).

  • Emphasis on importance due to prevalence and toxicological impact.

Learning Objectives

  • Understand mechanisms of action of various insecticides.

  • Explain clinical manifestations related to insecticide exposure.

  • Discuss treatment approaches for insecticide intoxications.

Types of Insecticides

Exposure Routes

  • Systemic Insecticides: Applied to soil, absorbed by plant roots, affecting edible portions.

  • Contact Insecticides: Directly sprayed on plants, killing insects upon contact.

Insecticide Families Discussed

  • Organophosphates and Carbamates

    • Affect acetylcholinesterase, leading to cholinergic toxicity.

  • Pyrethroids

    • Affect voltage-gated sodium channels, causing hyperexcitability.

  • Neonicotinoids

    • Mimic nicotine and affect nicotinic acetylcholine receptors in insects.

  • Isoxazolines

    • Antagonize GABA and glutamate-gated chloride channels in insects.

Organophosphates and Carbamates

Mechanism of Action

  • Inhibit acetylcholinesterase, leading to accumulation of acetylcholine.

  • Toxicity Spectrum: Varies widely from highly toxic (<50 mg/kg) to low (>1000 mg/kg).

Clinical Signs in Dogs

  • Overactivation of nicotinic receptors: Tremors, muscle weakness.

  • Overactivation of muscarinic receptors: Hypersalivation, miosis, diarrhea.

Diagnosis

  • Clinical signs of cholinergic toxicity, measurement of cholinesterase activity.

Treatment

  • Asymptomatic: Decontamination (soap, water, activated charcoal).

  • Symptomatic: Control seizures, use atropine for bradycardia and respiratory distress.

  • Specific antidote for organophosphate: 2-PAM (pralidoxime chloride).

Neonicotinoids

Overview

  • Effectively used for agricultural pests and flea control.

  • Highly toxic to beneficial non-target organisms, particularly pollinators.

Mechanism of Action

  • Mimics acetylcholine at nicotinic receptors, causing persistent activation.

  • Primarily affects insects due to differences in receptor structure.

Treatment

  • No specific antidote; symptomatic treatment is required.

Pyrethroids

Overview

  • Derived from chrysanthemum flowers; target insects with low toxicity to mammals.

Mechanism of Action

  • Prolongs opening of voltage-gated sodium channels, causing rapid neuronal firing.

Clinical Signs

  • Tremors, potential seizures.

Treatment

  • Symptomatic care, IV fluids, and possibly control of seizures and tremors.

Isoxazolines

Mechanism of Action

  • Antagonist that blocks chloride channels, leading to hyperexcitation in insects.

Safety and Precautions

  • Generally safe for mammals but should be used cautiously in animals with seizures.

Treatment

  • Supportive care for symptoms.

Summary of Insecticide Effects

Insecticide Class

Mechanism of Action

Target Site

Clinical Signs

Specific Treatment

Organophosphates, Carbamates

Inhibit acetylcholinesterase

Cholinergic synapses

Tremors, hypersalivation

Atropine, 2-PAM

Neonicotinoids

Mimic acetylcholine

Nicotinic receptors

Hyperexcitation, paralysis

Symptomatic

Pyrethroids

Prolong sodium channel activation

Neuronal membranes

Tremors, seizures

Symptomatic

Isoxazolines

Antagonists at chloride channels

GABA/glutamate channels

Hyperexcitation

Symptomatic

Conclusion

  • Various insecticide classes pose different toxicity risks and require distinct diagnostic and treatment approaches.

  • Understanding the mechanisms can aid in managing exposure cases effectively.