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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • A toxic syndrome involving the GI and renal systems, resulting primarily from the ingestion or dermal absorption of blistering agents containing inorganic mercury salts (e.g. mercuric iodide or mercuric chloride)
  • Toxicosis from ingesting seeds treated with mercury-containing fungicides is unlikely, because such fungicides are no longer used
  • Mercury binds to a variety of sulfhydryl-containing enzymes resulting in nonspecific cell injury and death

Signalment!!navigator!!

No breed, age, or sex predilections.

Signs!!navigator!!

  • Depression
  • Colic
  • Diarrhea
  • Weakness
  • Skin erosions, ulcerations, and crusting
  • Dehydration
  • Oliguria
  • Laminitis

Causes and Risk Factors!!navigator!!

  • Excessive application of mercury-containing blistering agent
  • Application of mercury-containing blistering agent to damaged skin
  • Failure to prevent the animal from ingesting a dermally applied mercury-containing agent
  • Application of mercury-containing blistering agent in combination with DMSO

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Lead toxicosis—likely evidence of neurologic dysfunction; measurement of whole-blood or tissue lead concentrations
  • Arsenic toxicosis—measurement of whole-blood, urine, or tissue arsenic concentrations
  • NSAID toxicosis—history of previous use; measurement of an NSAID in plasma or serum
  • Cantharidin toxicosis—evidence of cystitis; detection of cantharidin in stomach contents or urine
  • Quercus spp. (oak) toxicosis—detection of plant material in the GI tract; evidence of oak consumption
  • Ethylene glycol
  • Salmonellosis—fecal cultures
  • Ehrlichial colitis—serology
  • Acute cyathostomiasis—fecal egg counts
  • Clostridial colitis—isolation of pathogenic clostridia; identification of toxins
  • Antimicrobial-induced colitis (e.g. lincomycin, tetracycline)—history of drug use

CBC/Biochemistry/Urinalysis!!navigator!!

  • Increased packed cell volume
  • Hyperfibrinogenemia
  • Serum electrolyte changes—hyponatremia, hypochloremia, hyperphosphatemia, and hyperkalemia
  • Hyperglycemia
  • Azotemia
  • Urinalysis—glycosuria, proteinuria, isosthenuria, hematuria, waxy or granular casts
  • Occult blood in feces

Other Laboratory Tests!!navigator!!

  • Antemortem—measurement of mercury in urine or blood
  • Postmortem—measurement of mercury in liver or kidney tissue

Imaging!!navigator!!

N/A

Other Diagnostic Procedures!!navigator!!

N/A

Pathologic Findings!!navigator!!

Gross

  • Watery feces
  • Intraluminal hemorrhage
  • GI mucosal edema
  • Mucosal ulcerations in the oral cavity, stomach, and colon
  • Subcutaneous edema
  • Pale, soft, and swollen kidneys

Histopathologic

  • Acute, severe renal tubular necrosis
  • Severe, extensive ulcerative colitis and enteritis

Treatment ⬆ ⬇

TREATMENT

  • Remove source of mercury
  • Treat for dehydration, circulatory shock, and renal failure
  • Provide a bland diet containing reduced amounts of high-quality protein

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Enhance mercury elimination with a chelator:
    • Dimercaprol (British anti-Lewisite) is a classic mercury chelator—loading dose of 4–5 mg/kg by deep IM injection followed by 2–3 mg/kg every 4 h for 24 h and then 1 mg/kg every 4 h for 2 days; adverse reactions include tremors, convulsions, and coma
    • Succimer is a less toxic chelator—dose is not established for horses, but 10 mg/kg PO every 8 h is suggested
  • Control abdominal pain:
    • Flunixin meglumine (1.1 mg/kg IV every 12–24 h) or butorphanol tartrate (0.1 mg/kg IV every 3–4 h up to 48 h)
    • Xylazine hydrochloride (1.1 mg/kg IV) may be used in conjunction with butorphanol (0.01–0.02 mg/kg IV)
  • Demulcents—mineral oil; kaolin–pectin

Contraindications/Possible Interactions!!navigator!!

Use NSAIDs cautiously because of possible adverse GI and renal effects.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Monitor renal function.

Prevention/Avoidance!!navigator!!

  • Identify and properly dispose of the source of exposure
  • Avoid use of mercury-containing blisters

Possible Complications!!navigator!!

N/A

Expected Course and Prognosis!!navigator!!

  • Dependent on the severity of clinical signs
  • Renal impairment suggests a poor prognosis
  • 1 equine case report described brain neuronal degeneration
  • Long-term neurologic deficits are possible after recovery

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

N/A

Age-Related Factors!!navigator!!

N/A

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

  • Most forms of mercury can cross the placenta
  • The significance of fetal exposure after use of mercury salts on pregnant mares is unknown

Abbreviations!!navigator!!

  • DMSO = dimethylsulfoxide
  • GI = gastrointestinal
  • NSAID = nonsteroidal anti-inflammatory drug

Suggested Reading ⬆ ⬇

Guglick MA, MacAllister CG, Chandra AM, et al. Mercury toxicosis caused by the ingestion of a blistering compound in a horse. J Am Vet Med Assoc 1995;206:210–213.

Author(s) ⬆

Authors: Arya Sobhakumari and Robert H. Poppenga

Consulting Editors: Wilson K. Rumbeiha and Steve Ensley