Pyelonephritis (Bacterial Infection of the Kidney) in Cats

What is Pyelonephritis?

Pyelonephritis is an upper urinary tract infection that involves the kidneys and ureters (the tubes that carry urine from the kidneys to the bladder).

Urinary tract infections are fairly uncommon in cats. When these infections do occur, they generally involve the bladder and urethra (the tube that transports the urine from the bladder out of the body). These are described as lower urinary tract infections. Pyelonephritis occurs more commonly in older cats, and there is no difference in frequency between females than males.

What are the signs of pyelonephritis?

Many cats have no clinical signs of pyelonephritis, but they may have signs of lower urinary tract disease. The signs of lower urinary tract infection include:

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

Additional signs of upper urinary tract infection include pain when the kidneys or abdomen are palpated (examined by touch) during the physical examination, and fever. 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, Leptospira and Pseudomonas, all of which frequently infect the lower urinary tract and may move up into the upper urinary tract. Less commonly, bacteria that can grow in a low- or no oxygen environment may cause pyelonephritis, as can fungal organisms.

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, which is backflow of urine from the bladder back into the ureters
• Renal dysplasia, which is the abnormal development of the kidneys from birth

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

• Diabetes mellitus, which causes glucose (sugar) in the urine, making the urine attractive to bacteria
• Medications that contain steroids
• Kidney failure
• Catheterization of the urethra
• Urine retention
• Bladder or kidney stones
• Underlying cancer
• Creation of a new urinary opening in the urethra (urethrostomy)

How is pyelonephritis diagnosed?

Pyelonephritis is best diagnosed by obtaining a urine culture. In addition, blood analysis is important to help 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?

Cats with pyelonephritis are usually treated as outpatients unless they have bacteria circulating in their blood, causing septicemia, or they have clinical signs of kidney failure. The specific treatment of pyelonephritis depends on the underlying cause. 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 re-positioned surgically to properly drain urine into the bladder. If the upper urinary tract is blocked by a urinary tract stone in a cat with bacterial infection/inflammation of the kidneys, it may rapidly progress to kidney failure, sepsis and death. This is a medical emergency and requires immediate veterinary intervention. Surgery may be required.

Antibiotics to treat pyelonephritis are chosen after 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 10–14 days, but treatment may be extended for several weeks, if needed.

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

Urinalyses and urine cultures are repeated one to two weeks after antibiotic therapy concludes. Rechecking lab tests three months and six months after treatment is advised. Potential complications of pyelonephritis include kidney failure, recurrent kidney infections, and bacteria in the blood causing infection in 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 with appropriate treatment 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.