Toxicity: mercury in Horses (Equis) | Vetlexicon
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Toxicity: mercury

ISSN 2398-2977


Synonym(s): Mercury poisoning

Introduction

  • Cause: elemental mercury, mercury salts, organomercurials. Mercury blistering agents used historically.
  • Signs: mercury salts: acute erosive and ulcerative dermatitis, stomatitis, renal failure, shock; elemental and organomercurials: chronic neurologic signs.
  • Diagnosis: history of exposure, clinical signs and lesions, analytical chemistry.
  • Treatment: remove source and clean affected skin (wear personal protection), and chelation.
  • Prognosis: poor.

Presenting signs

Acute presentation

Geographic incidence

  • Certain areas of the United States are more likely to have high environmental concentrations of mercury:
    • Great Lakes area.
    • South Florida.
    • Environmental mercury unlikely to be associated with clinical toxicosis in horses.

Breed/Species predisposition

  • Performance horses that are more likely to be treated with blistering agents.

Public health considerations

  • Mercury is toxic to humans:
    • Wear personal protective equipment when decontaminating the patient.
    • Contact a local public health agency for assistance in decontaminating facilities.
    • Mercury testing of exposed humans could be needed.
  • Mercury containing products are considered toxic waste and require proper disposal.

Cost considerations

  • Extensive supportive care and chelation therapy.
  • Poor prognosis for full recovery.

Special risks

  • Use of dimethylsufoxide (DMSO) Dimethyl sulfoxide with blistering agents increases absorption.
  • Secondary infections possible.
  • Laminitis Foot: laminitis reported.

Pathogenesis

Etiology

  • Mercury salts:
    • Used in blistering agents:
      • Dermal exposure.
      • Oral exposure from licking.
      • Most common source, historically.
    • Corrosive.
    • Nephrotoxic.
  • Organic mercury:
    • Methymercury, dimethylmercury, others: environmental sources.
    • Peripheral neuropathy.
    • Central nervous system dysfunction.
  • Elemental mercury:
    • Found in old thermometers, barometers.
    • Poor absorption from the gastrointestinal tract (low risk)
    • Inhalation results in rapid absorption.
    • Central nervous system and renal dysfunction.

Predisposing factors

General

  • Use of blistering agents containing mercury; these products are illegal in the United States.

Specific

  • Use of blistering agents containing mercury.
  • Respiratory exposure to elemental mercury through broken thermometers, barometers:
    • Unlikely to be clinically significant.
    • Occasional reports of stored elemental mercury causing exposure in humans.
  • Exposure to organic mercury compounds is unlikely to be of clinical relevance.  

Pathophysiology

  • Mercuric salts:
    • Water soluble.
    • Corrosive to skin and mucous membranes.
    • Absorbed mercury ions bind sulfhydryl groups: inactivation of enzymes.
    • Salivary excretion of mercury: delayed stomatitis can occur.
    • Renal excretion:
      • Accumulates in proximal convoluted tubule.
      • Necrosis of tubular epithelium.
  • Organic mercury:
    • Inhibits protein synthesis in the brain.
    • Generates reactive oxygen species.

Timecourse

  • Mercury salts:
    • Onset within 48 h of administration of blistering agents.
    • Possible outcomes:  
  • Elemental and organic mercury: chronic exposure most likely.

Epidemiology

  • Historically associated with use of blistering agents containing mercury salts.
  • Mercury-containing blistering products are illegal in the United States.

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 VetMedResources.
  • Casteel S W (2001) Metal toxicosis in horses. Vet Clin North Am Equine Pract 17 (3), 514 PubMed
  • Guglick M A et al (1995) Mercury toxicosis caused by ingestion of a blistering compound in a horse. JAVMA 206 (2), 210-214 PubMed.
  • Markel M D, Dyer R M & Hattel A L (1984) Acute renal failure associated with application of a mercuric blister in a horse. JAVMA 185 (1), 92-94 VetMedResource.

Other sources of information

  • Gupta R C (2012) Ed. Mercury. In: Veterinary Toxicology Basic and Clinical Principles. 2nd edn. Academic Press, USA. pp 537-543.
  • Puls R (1994) Mineral Levels in Animal Health. Sherpa Publishing, Canada. pp 185.