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 and soil.
Young dogs are commonly poisoned by accidental ingestion of lead-containing objects such as sinker weights and small lead batteries.
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. It is also a known mutagen and teratogen, resulting in fetal deformities.
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.
Clinically affected dogs are usually young and typically present with lethargy, anorexia and vomiting. 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.
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.
Diagnosis is based on clinical history of exposure, presenting symptoms, and finding of elevated lead levels in vomitus or blood. Lead levels > 0.35 ppm (> 20 μg/dL) in the blood and > 10 ppm in liver or kidney are considered diagnostic. Elevated levels of δ-aminolevulinic acid and free erythrocyte protoporphyrin are also considered diagnostic.
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.
- Dr Dolen
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