Pyelonephritis in Cats

By Tammy Hunter, DVM; Robin Downing, DVM, DAAPM, DACVSMR, CVPP, CRPP

What is Pyelonephritis? 

Bacterial urinary infections are fairly uncommon in cats. When these infections do occur, they generally involve the bladder and urethra (the tube that leads the urine out of the body) and are described as lower urinary tract infections.

Pyelonephritis is more accurately described as an upper urinary tract infection because it affects the kidneys. The upper urinary tract consists of the kidneys and the ureters (the tubes that carry from the kidneys to the bladder).

There seems to be no specific age predisposition for pyelonephritis in cats, and there is no difference in frequency between females than males.

Many cats have no clinical signs when they have pyelonephritis, although they may have signs of lower urinary tract disease. Signs of urinary tract infection may include:

  • Increased drinking and increased urination
  • Difficult/painful urination
  • Frequent urination of small volumes of urine
  • Inappropriate urination (urinating outside the litterbox)
  • Slow, uncomfortable urination

Additional signs are specific to pyelonephritis may include the presence of a fever and pain when the kidneys are palpated during the physical examination. Also, one or both kidneys may be abnormal in size.

What causes pyelonephritis? 

Pyelonephritis is usually caused by a bacterial infection that moves up the urinary tract from the bladder to the kidneys. The bacteria most commonly implicated are Escherichia coli and Staphylococcus. Other bacteria that may be found include Proteus, Streptococcus, Klebsiella, Enterobacter, and Pseudomonas, which frequently infect the lower urinary tract and may move up into the upper urinary tract. Less commonly, anaerobic bacteria (bacteria that can live and grow in a low/no oxygen environment) or fungal organisms may cause pyelonephritis.

Are there risk factors for pyelonephritis? 

There are several developmental conditions that increase the risk of pyelonephritis:

  • Ectopic ureters - a condition in which the ureters do not attach to the bladder properly
  • Vesicoureteral reflux - backflow of urine from the bladder back into the ureters
  • Renal dysplasia - abnormal development of the kidneys

There are several medical conditions and medical procedures that increase the likelihood of urinary tract infection including:

  • Diabetes mellitus (causes glucose making the urine attractive to bacteria)
  • Kidney failure
  • Urine retention
  • Bladder or kidney stones
  • Administration of medications containing steroids
  • Catheterization of the urethra
  • Urethrostomy (creation of a new urinary opening in the urethra)

How is pyelonephritis diagnosed? 

Pyelonephritis is best diagnosed by obtaining a urine culture. In addition, blood analysis will be important to determine if kidney failure has occurred. Imaging the kidneys using radiographs (x-rays) and/or ultrasound may show changes supportive of a diagnosis of pyelonephritis.

How is pyelonephritis treated? 

The specific treatment of pyelonephritis depends on the underlying cause.

Cats with pyelonephritis are usually treated as outpatients unless they have septicemia (bacteria circulating in the blood), or clinical signs of kidney failure. If cats with pyelonephritis also have underlying kidney disease, their treatment may include a kidney support diet (e.g., Hill’s Prescription Diet k/d® Feline).

Ectopic Ureters are repositioned surgically, to properly drain urine into the bladder. Urinary tract obstruction caused by a bladder stone is a medical emergency and is most often treated with surgery.

Antibiotics to treat pyelonephritis are chosen based on testing the urine for bacteria and antibiotic sensitivity. The chosen antibiotic should kill bacteria, be present at appropriate levels in the blood and in the urine, and should not be toxic to the kidneys. Antibiotics are generally given for 4–6 weeks to treat pyelonephritis.

What kind of follow-up care can I expect for my cat? 

Repeated urinalyses and urine cultures are done during antibiotic treatment, generally 5–7 days into treatment and 1–4 weeks after antibiotic therapy concludes. Potential complications of pyelonephritis include kidney failure, recurrent kidney infections, and infection spreading to other parts of the body (such as the lining of the heart or the joints).

Overall, cats with sudden pyelonephritis do well and return to normal health unless they also have kidney stones, chronic kidney disease, urinary tract obstruction, or cancer in the urinary tract.

Cats with chronic or recurrent pyelonephritis may be difficult to cure, and their prognosis is more serious. If pyelonephritis is not identified and treated appropriately, permanent kidney damage and chronic kidney disease with kidney failure may result.

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