Serious severity
Pyelonephritis (Kidney Infection)
A bacterial infection of one or both kidneys, usually spreading upward from the bladder, that can cause sudden illness or quietly damage kidney tissue over time.
⚠️ Common symptoms
Pyelonephritis is an infection that has reached the kidneys themselves, the organs that filter and concentrate the blood into urine. Most cases begin lower down, in the bladder, and the bacteria then climb the ureters into the kidney tissue. Because the kidneys are so vital, an infection there is more serious than a simple bladder infection.
The condition can be acute and dramatic, with fever, back pain and a visibly unwell cat, or it can smoulder quietly, gradually eroding kidney function without obvious signs until damage has been done. This is why vets take suspected kidney infections seriously and often reach for a urine culture, which identifies the exact bacterium and the antibiotic most likely to clear it.
Treatment is usually a prolonged antibiotic course, sometimes several weeks, because the deep kidney tissue is harder to sterilise than the bladder. Supporting the cat with fluids and pain relief, and dealing with any underlying stone, obstruction or disease that let the infection take hold, gives the best chance of a full recovery and of protecting long-term kidney health.
🔍 Causes
It is most often caused by bacteria travelling up the urinary tract from the bladder to the kidneys. Factors that make it more likely include bladder stones, urinary obstruction, diabetes, and pre-existing kidney disease that lets infection take hold.
🛡 Prevention
Prompt treatment of any lower urinary tract infection, good hydration, and management of predisposing conditions like diabetes or stones all lower the risk. Encouraging water intake with fountains and wet food helps keep the urinary system flushed.
💊 Treatment
The mainstay is a course of appropriate antibiotics, ideally chosen from a urine culture so the right drug is used for long enough — kidney infections often need several weeks of treatment. Fluids support the kidneys, pain relief keeps the cat comfortable, and any predisposing factor such as a stone or urinary obstruction is addressed.
⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.