Struvite urinary calculi, which are composed of
magnesium,
ammonium, and
phosphate, can cause complications including
sepsis and
renal failure.
Struvite calculi were identified within the urinary bladder and renal pelvis of 2 Long-Evans rats that died within days after arrival from a commercial vendor. The remaining rats in the shipment were screened by physical examination, radiography, and ultrasonography, revealing an additional 2 animals that were clinically affected. These rats were euthanized, necropsied, and yielded similar findings to those from the first 2 rats. In addition, urine samples had an alkaline pH and contained numerous bacteria (predominantly Proteus mirabilis), leukocytes, and crystals. All
calculi were composed completely of
struvite. Another 7 rats in the shipment had alkaline urine with the presence of blood cells; 6 of these rats also had abundant
struvite crystals, and P. mirabilis was cultured from the urine of 3 rats. Further investigation by the vendor identified 2 of 100 rats with
struvite calculi from the same colony. Although no specific cause could be implicated, the fact that all the affected rats came from the same breeding area suggests a genetic or environmental triggering event; a contribution due to diet cannot be ruled out. Our findings suggest that the affected rats had metabolic disturbances coupled with
bacterial infection that predisposed them to develop
struvite calculi. During sudden increases of
struvite urinary calculi cases in rats, urine cultures followed by appropriate surgical intervention and
antibiotic therapy is warranted. Additional factors, including diet, merit attention as well.