Pyelonephritis (Bacterial Infection of the Kidney) in Dogs

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 common in dogs, although they more commonly involve the bladder and urethra (the tube that transports urine from the bladder out of the body). These are described as lower urinary tract infections. Pyelonephritis tends to occur more often in older dogs. Urinary tract infections, in general, affect female dogs more than males.

What are the signs of pyelonephritis?

Many dogs 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 (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 abdomen is 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, Leptorspira 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 or may attach to reproductive organs instead of the bladder
• 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
• Cushing’s disease (hyperadrenocorticism), or overactive adrenal glands, which causes increased levels of steroids in the body, leading to a decrease in the body’s resistance to infection
• Medications that contain steroids
• Kidney failure
• Catheterization of the urethra
• Urine retention
• Bladder or kidney stones
• Underlying cancer
• Surgical removal of the penis and creation of a new opening to the urethra (perineal urethrostomy)

How is pyelonephritis diagnosed?

Pyelonephritis may be diagnosed with a combination of presenting signs, urine culture, and worsening of blood kidney values, which indicates a disease process in the kidneys.

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 includes 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. 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 at least 10–14 days to treat pyelonephritis.

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

Urinalyses and urine cultures are repeated one to two weeks after antibiotic therapy concludes, and again three months and six months after treatment. 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.