Histological and ultrastructural studies of renal lesions in Babesia canis infected dogs treated with imidocarb.

Histological and electron microscopic examinations of the kidneys of 8 dogs suffering from fatal, naturally acquired Babesia canis infection and nephropathy are presented. Seven animals were treated with imidocarb dipropionate on average 4.5 days prior to death. Severe anaemia was present only in 2 cases. Degenerative histological changes observed mostly in the proximal convoluted tubules included vacuolar-hydropic degeneration, necrosis and detachment of renal tubular epithelial (RTE) cells from the basement membrane. Necrotic debris occasionally formed acidophilic casts within the tubules. In some cases, necrosis of the whole tubule was observed. Haemoglobin casts in the tubules and haemoglobin droplets in RTE cells seldom appeared. No significant histological changes were seen in the glomeruli. Ultrastructural lesions in RTE cells included nuclear membrane hyperchromatosis, karyopyknosis, karyolysis, swelling or collapse of mitochondria with fragmentation of cristae and vacuolar-hydropic degeneration in the endoplasmic reticulum and microvilli. Nuclear oedema was also observed. Many RTE cells exhibiting necrosis collapsed. Vacuolar-hydropic degeneration and necrosis were also observed in the glomerular and interstitial capillary endothelium. The severe acute tubular necrosis described in this study is probably the result of hypoxic renal injury. Systemic hypotension leading to vasoconstriction in the kidneys might be the most important cause of renal hypoxia in B. canis infections, but anaemia may also contribute to inadequate oxygenation. Imidocarb should be applied with caution in patients with possible renal involvement until further data become available on its potential nephrotoxicity in dogs.