Idiopathic cystitis (IC) is the single most important cause of frequent and painful urination, bloody urine, and inappropriate urination in male and female cats. It affects the urinary bladder and urethra (the lower urinary tract) of cats and is sometimes referred to as FLUTD/FUS. The researchers estimate that this disorder affects nearly a half a million cats annually. Despite extensive study, the specific underlying cause(s) of idiopathic cystitis remain(s) unknown. Microscopic evidence suggests that a virus, known as feline calicivirus, may have a causative role in this disease. In 1998, the researchers isolated a calicivirus from urine obtained from a cat with IC. Genetic analyses, funded by the Winn Foundation, indicated that this isolate was distinct from other calicivirus. They have now isolated a second urine calicivirus from an affected cat. It is unknown whether these urine calicivirus cause IC or merely represents coincidental shedding of a respiratory or vaccine strain of calicivirus. Through further genetic analysis, the researchers will learn whether the second urine calicivirus isolate is related to the first urine isolate or to other feline calicivirus. If these urine caliciviruses are unique, and if subsequent investigations can establish a cause-and-effect relationship with idiopathic cystitis, then specific diagnostic tests, antiviral drugs, and/or more effective calicivirus vaccines could be developed to treat idiopathic cystitis or FLUTD.