Pyelonephritis (Bacterial Infection of the Kidney) in Dogs

By Krista Williams, BSc, DVM, CCRP; Tammy Hunter, DVM; Robin Downing, DVM, DAAPM, DACVSMR, CVPP, CRPP

What is pyelonephritis?

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

Urinary tract infections are fairly common in dogs, although they generally involve the bladder and urethra (the tube that transports the urine from the bladder to the outside of the body) and are described as lower urinary tract infections (see handouts “Cystitis in Dogs” and “Urinary Tract Infections (UTIs) in Dogs” for information on infections affecting the lower urinary tract).

There seems to be no specific age predisposition for pyelonephritis in dogs. Urinary tract infections, in general, affect more females than males.

What are the signs of pyelonephritis?

Many dogs have no clinical signs when they have pyelonephritis, although 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 (particularly noticeable in dogs that have previously been well house trained)
  • slow, uncomfortable urination

Additional signs of upper urinary tract infection include fever, reduced appetite, lethargy and pain when the kidneys or abdomen are palpated (examined by touch) 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, bacteria that can live and grow in a low/no oxygen environment, as well as fungal organisms may cause pyelonephritis.

Are there risk factors for pyelonephritis?

There are several developmental conditions that increase the risk for pyelonephritis.

  • Ectopic ureters describe a condition in which the ureters do not attach to the bladder properly or may attach to reproductive organs instead of the bladder.
  • Vesicoureteral reflux describes backflow of urine from the bladder back into the ureters.
  • Renal dysplasia describes abnormal development of the kidneys from birth.

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

  • Diabetes mellitus, causing glucose (sugar) in the urine, making the urine very attractive to bacteria.
  • Cushing's disease (hyperadrenocorticism), or overactive adrenal glands, causing increased levels of steroids in the body and decreasing the body's resistance to infection.
  • Administration of medications containing steroids
  • Kidney failure
  • Catheterization of the urethra
  • Urine retention
  • Bladder or kidney stones
  • Surgical removal of the penis and creation of a new opening to the urethra (perineal urethrostomy)

How is pyelonephritis treated?

Dogs 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 dogs with pyelonephritis also have kidney disease, part of their treatment will include a diet designed to support the kidneys (e.g., Hill's® Prescription Diet® k/d®, Royal Canin® Veterinary Diet Canine Renal Support, Purina® ProPlan® Veterinary Diet NF Kidney Function®, or Rayne Clinical Nutrition™ Adult Health-RSS™).

Ectopic ureters are repositioned surgically to properly drain urine into the bladder. Blockage of the upper urinary tract by a urinary tract stone in a dog with bacterial infection/inflammation of the kidneys may rapidly progress to generalized disease and septicemia. This 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 at least 10-14 days to treat pyelonephritis.

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

Serial urinalyses and urine cultures are done during antibiotic treatment, generally 5 to 7 days into treatment and 1 to 4 weeks after antibiotic therapy concludes. 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, dogs 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.

Dogs 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 may result.

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