Subclinical renal oxalosis in wild-caught Japanese macaques (Macaca fuscata)

Various degrees of crystal deposition were found in the kidneys of 12 out of 59 Japanese macaques (Macaca fuscata) caught in the wild in Gifu, Japan. The needle- or rod-shaped crystals, which were radially arranged and occurred in the lumen and epithelium of the renal (mainly the proximal) tubules, were birefringent under polarized light. They stained with alizarin red S at a pH of 7.0 but not 4.2, and were identified as calcium oxalate. The morphological features of the renal lesions were similar to those previously reported in oxalate poisoning, and it was believed that the macaques ingested the oxalate in plants.