Plasma biochemistry and urinalysis variables of koalas (Phascolarctos cinereus) with and without oxalate nephrosis

Abstract

Background Oxalate nephrosis is a highly prevalent disease in the Mount Lofty Ranges koala population in South Australia, but associated clinicopathologic findings remain undescribed. Objectives The aims of this study were to determine plasma biochemical and urinalysis variables, particularly for renal function and urinary crystal morphology and composition, in koalas with oxalate nephrosis. Methods Blood and urine samples from Mount Lofty Ranges koalas with oxalate nephrosis were compared with those unaffected by renal oxalate crystal deposition from Mount Lofty and Kangaroo Island, South Australia and Moggill, Queensland. Plasma and urine biochemistry variables were analyzed using a Cobas Bio analyzer, and urinary oxalate by high‐performance liquid chromatography. Urinary crystal composition was determined by infrared spectroscopy and energy dispersive X‐ray analysis. Results Azotemia (urea > 6.6 mmol/L, creatinine > 150 μmol/L) was found in 93% of koalas with oxalate nephrosis (n = 15). All azotemic animals had renal insufficiency (urine specific gravity [USG] < 1.035), and in 83%, USG was < 1.030. Koalas with oxalate nephrosis were hyperoxaluric compared with Queensland koalas (P < .01). Urinary crystals from koalas with oxalate nephrosis had atypical morphology and were composed of calcium oxalate. Mount Lofty Ranges koalas unaffected by renal oxalate crystal deposition had renal insufficiency (43%), although only 14% had USG < 1.030 (n = 7). Unaffected Mount Lofty Ranges and Kangaroo Island koalas were hyperoxaluric compared with Queensland koalas (P < .01). Conclusions Koalas with oxalate nephrosis from the Mount Lofty Ranges had renal insufficiency, hyperoxaluria, and pathognomonic urinary crystals. The findings of this study will aid veterinary diagnosis of this disease.

Necropsy findings of koalas from the Mount Lofty Ranges population in South Australia

“…That this prevalence is lower than has been found previously (55%) may be related to the larger cohort in the current study. Oxalate nephrosis has also been reported in other populations of koalas, but at only < 3% prevalence in New South Wales (n = 235) and up to 5% in Queensland (n = 20) . Oxalate nephrosis was found to be common in young koalas of TWC I, similar to an earlier study, and also in females, whereas previously no association with sex was identified.…”

What is your diagnosis? Unusual urinary crystals from a cat

“…Calcium oxalate crystals can exist in many forms, including envelope‐shaped dihydrate crystals (weddellite) and rod, “picket fence,” or dumbbell‐shaped monohydrate crystals (whewellite) . Unusual calcium oxalate crystals were recently reported in Koala urine and displayed a similar morphology to those reported here …”

Oxalate‐degrading bacteria, including Oxalobacter formigenes, colonise the gastrointestinal tract of healthy koalas (Phascolarctos cinereus) and those with oxalate nephrosis

“…1,27 A lower abundance of oxalate-degrading bacteria could increase the amount of oxalate absorbed from the gut into the bloodstream and increase the risk of renal oxalate deposition. in the Mount Lofty Ranges koalas compared with the two Queensland koalas in the previous study 23 could be partly related to the higher occurrence of oxalate nephrosis in Mount Lofty koalas.…”

“…in the Mount Lofty Ranges koalas compared with the two Queensland koalas in the previous study 23 could be partly related to the higher occurrence of oxalate nephrosis in Mount Lofty koalas. 1,27 A lower abundance of oxalate-degrading bacteria could increase the amount of oxalate absorbed from the gut into the bloodstream and increase the risk of renal oxalate deposition. This, coupled with the findings of a previous study in which dietary leaf oxalate content in Mount Lofty Ranges eucalyptus leaves was approximately double that of those in Moggill, Queensland, also supports this.…”