Lead toxicity

From Dog
A common source of lead poisoning - residues of lead shots from accidental shooting[1]

Lead is ubiquitous in the environment as a result of mining and industrialization and is commonly found in oil-based paint, linoleum, grease, lead sinker weights used for fishing, lead shot, pollution, drinking water[2] and soil[3].

Young dogs are commonly poisoned by accidental ingestion of lead-containing objects such as sinker weights and small lead batteries[4].

Poisoning by this metal (plumbism) occurs when it is absorbed following oral ingestion, where it is then redistributes to bone. During its systemic redistribution, it interferes with sulfhydryl-containing enzymes, thiol-based enzymes within erythrocytes, antioxidant enzyme function and mitochondrial function, leading to capillary damage, edema, acute erythrocyte breakdown, immunosuppression, and toxic effects on multiple organs including the liver, kidney and brain[5]. It is also a known mutagen and teratogen, resulting in fetal deformities[6].

Elevated levels of lead can be found in dogs in areas where renovations of buildings or industrial regions results in sandblasting and removal of lead-based paints, but clinical signs may not be apparent in cases of chronic exposure[7].

Clinically affected dogs are usually young and typically present with lethargy, anorexia and vomiting[8]. Severely affected dogs may present with more dramatic signs such as acute blindness, abdominal pain, vomiting, diarrhea, ataxia, ptyalism, muscle tremors, infertility, jaw chattering, mental depression, opisthotonus and seizures[9].

Hematological evaluation of blood samples may reveal acute renal injury characterized by basophilic stippling, nonregenerative hypochromic anemia with anisocytosis, poikilocytosis, polychromasia and metarubricytosis. Serum biochemistry shows varying degrees of hyperkalemia, azotemia and elevated ALT, AST and GGT[10].

Diagnosis is based on clinical history of exposure, presenting symptoms, and finding of elevated lead levels in vomitus or blood[11]. Lead levels > 0.35 ppm (> 20 μg/dL) in the blood and > 10 ppm in liver or kidney are considered diagnostic[12][13]. Elevated levels of δ-aminolevulinic acid and free erythrocyte protoporphyrin are also considered diagnostic[14].

Histological examination of organs usually reveals non-specific degeneration of the epithelial cells of the urinary tubules, the endothelial cells of the renal capillaries and the hepatocytes[15].

A differential diagnosis would include pancreatitis, tetanus, meningioma, rabies, distemper and hepatitis[16].

Treatment usually requires chelation therapy with calcium disodium edetate given parenterally at 110 mg/kg/day for 3 days, and use of adjunctive drugs such as thiamine and D-penicillamine.

Thiopentone or diazepam may be required to control convulsions, and addition of antioxidants such as acetylcysteine.

References

  1. Dr Dolen
  2. Marin C (2006) What is your diagnosis? Lead poisoning in a dog caused by lead in a drinking tap. J Small Anim Pract 47(7):413-415
  3. Mañay N et al (2008) Lead contamination in Uruguay: the "La Teja" neighborhood case. Rev Environ Contam Toxicol 195:93-115
  4. Hamir AN et al (1982) The effects of age and diet on the absorption of lead from the gastrointestinal tract of dogs. Aust Vet J 58:266-268
  5. Zook BC & Carpenter JL (1977) Lead poisoning. In: Kirk RW, ed. Current Veterinary Therapy: Small Animal Practice, 6th ed. Philadelphia: WB Saunders. pp:128-133.
  6. Lange JH et al (2003) Exposure to lead and an old way of counting. Environ Health Perspect 111(10):A510-A511
  7. Dowsett R & Shannon M (1994) Childhood plumbism identified after lead poisoning in household pets. N Engl J Med 331:1661–1662
  8. Huerter L (2000) Lead toxicosis in a puppy. Can Vet J 41(7):565-567
  9. Prescott CW (1983) Clinical findings in dogs and cats with lead poisoning. Aust Vet J 60:270-271
  10. Ghisleni G et al (2004) Blood lead levels, clinico-pathological findings and erythrocyte metabolism in dogs from different habitats. Vet Hum Toxicol 46(2):57-61
  11. Srebocan E et al (2001) Lead poisoning in a dog - a case report. Berl Munch Tierarztl Wochenschr 114(5-6):216-217
  12. Bischoff K et al (2010) Animals as sentinels for human lead exposure: a case report. J Med Toxicol 6(2):185-189
  13. Swarup D et al (2000) Blood lead and cadmium in dogs from urban India. Vet Hum Toxicol 42(4):232-233
  14. Merck Veterinary Manual
  15. Papaioannou N et al (1998) Histopathological lesions in lead intoxicated dogs. Vet Hum Toxicol 40(4):203-207
  16. Rothuizen J & van den Ingh TS (1998) Hepatitis in dogs; a review. Tijdschr Diergeneeskd 123(8):246-252