ISSN 2398-2969      

Toxicity: insecticide

Clapis

Synonym(s): Pyrethroid toxicity


Introduction

  • Natural and synthetic pyrethroids are commonly used as insecticides:
    • Pyrethrins are natural derivatives from chrysanthemums, while pyrethroids are their synthetic structurally-related counterparts.
    • Rapidly degraded by UV light. Newer compounds are more photostable and half-lives may be as much as 30 days (for cypermethrin).
    • Rapidly metabolized by animals.
    • Permethrin is licensed as Xenex® to treat external parasites in rabbits.
  • Cause: direct pyrethroid toxicity due to exposure, and/or toxicity from other ingredients in formulations, eg insect growth regulators, synergists, solvents or other carriers.
  • Signs: dermal lesions, lethargy, anorexia, neurological signs.
  • Diagnosis: history of exposure.
  • Treatment: supportive care.
  • Prognosis: depends on exposure dose and severity of clinical signs at presentation.

Pathogenesis

Etiology

  • Exposure can occur by oral and dermal route and by inhalation
  • LD50 for permethrin in rabbits via dermal exposure >2,000 mg/kg.
  • Cis-isomer of permethrin is more toxic than transisomer.
  • Exposure route of pyrethrins is important:
    • Poor absorption via gastrointestinal tract and skin.
    • Toxicity usually seen after exposure via respiratory route.

Predisposing factors

General

  • Rabbits have extensive grooming habits and therefore may ingest any chemical applied to the skin or coat.

Specific

  • Small individuals may easily be overdosed with application of a licensed product.

Pathophysiology

  • Dermal irritation:
    • Initially mildly reddened area at site of application.
    • May progress to severe lesions with redness, weeping open sores and local fur loss of varying degrees.
  • Ocular application results in conjunctivitis.
  • High concentrations result in more severe toxic effects.
  • In nerve axons, pyrethrins reversibly prolong sodium conductance. Repetitive nerve discharges result in the nervous signs seen at higher levels of exposure.
  • The permethrin cypermethrin has been shown to induce oxidative stress in rabbits.
  • Synthetic pyrethroids have shown to have toxic effects on the reproductive tract of rabbits.

Timecourse

  • Onset within hours of exposure, depending on dose.
  • For most animals, it is possible to metabolize/excrete pyrethrins within a few days.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Vardavas A I, Fragkiadaki P, Alegakis A K et al (2016) Downgrading the systemic condition of rabbits after long term exposure to cypermethrin and piperonyl butoxide. Life Sci 145, 114-120 PubMed.
  • Murphy L A (2015) Environmental toxicology: considerations for exotic pets. J Exotic Pet Med 24 (4), 390-397 VetMedResource.
  • Sallam M A, Ahmad M, Ahmad I et al (2015) Toxic effects of cypermethrin on the reproductive functions of female rabbits and their amelioration with vitamin E and selenium. Pakistan Vet J 35 (2), 193-196 ResearchGate.
  • Yousef M I (2010) Vitamin E modulates toxicity of pyrethroid lambda-cyhalothrin in male rabbits. Food Chem Toxicol 48 (5), 1152-1159 PubMed.
  • Dahamna S, Harzallah D, Guemache A et al (2009) Biochemical investigation of cypermethrin toxicity in rabbits. Comm Agric Appl Biol Sci 74 (1), 149-153 PubMed.
  • Johnston M S (2008) Clinical toxicoses of domestic rabbits. Vet Clin North Am Exotic Anim Pract 11 (2), 315-326 PubMed.

Other sources of information

  • Gupta R C (2012) Ed Veterinary Toxicology: Basic and Clinical Principles. Academic Press.

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