Pyelonephritis is an inflammation of the renal pelvis (from the Greek nephros: “kidney”, pýlos: “pelvis” and -itis: “inflammation”). Pyelonephritis is usually caused by bacteria that have travelled along the urethra, through the urinary bladder and the ureters, and into the renal pelvis. This is why acute pyelonephritis can be preceded by an infection of the bladder. Pain in the kidney area, high fever and general weakness can be symptoms of pyelonephritis, which may also be accompanied by changes in the urine. If acute pyelonephritis is not cured completely, it can become chronic, which might cause irreparable damage to the kidney tissue.