Kidney infections in dogs, medically known as pyelonephritis, are a serious medical condition that warrant a veterinary visit as soon as dog owners notice the earliest signs. In order to better understand kidney infections in dogs, it helps to take a closer look into how a dog's kidneys work, and how disease can impact them. Veterinarian Dr. Ivana Crnec shares information about kidney infections in dogs, symptoms in affected dogs and treatment options.
The Role of Kidneys in Dogs
All of the activities that a dog performs, from eating and breathing to running and jumping, are made possible by chemical reactions in its body cells. These chemical reactions produce wastes that gradually collect in the bloodstream. For a dog to stay healthy, its urinary tract must filter out these wastes from the blood and excrete them.
The dog’s urinary tract consists of two kidneys, two ureters, one bladder and one urethra. Generally speaking, all of these organs are responsible for cleansing the organism form waste products.
The cleansing process starts in the kidneys. They are supplied with blood by the renal artery and clean blood leaves the kidneys via the renal vein. Each kidney contains about 400.000 individual cleansing units called "nephrons."
Each nephron is made up of a globe of capillaries (tiny blood vessels) called a glomerulus and a long but thin tube called the renal tubule. Pores in the glomerulus allow only some substances in the blood to pass through. For example, red blood cells are too large to pass through the pores. Smaller molecules and fluids can pass from the glomerulus into the renal tubule, where useful substances such as glucose are reabsorbed into the bloodstream. The fluid remaining in the renal tubule, called urine, is a mixture of wastes, such as urea (produced by protein metabolism) and other substances not required by the body, such as excess water and salts.
This constant filtration of the blood helps to regulate fluid levels. If a dog drinks more water than needed for its body’s requirements, the excess is excreted in urine. On the other hand, if the dog needs to conserve water, the kidneys make the urine more concentrated by reabsorbing more water from the renal tubules.
The amount of water reabsorbed or excreted by the kidneys is controlled by a hormone called antidiuretic hormone (ADH), which is produced by the pituitary gland at the base of the brain, in response to the blood’s concentration.
As well as regulating water balance, if the blood becomes too acidic or alkaline, the kidneys change the urine’s acidity level to restore the correct balance. The kidneys also secrete hormones, such as erythropoietin, which stimulates the production of red blood cells.
Signs of Kidney Infections in Dogs
Changes in the dog’s habits of urination may indicate a problem in the urine tract. The most common signs indicating kidney issues are:
- Increased or more frequent urination
- Increased thirst
- Changes in the color of the urine
- Pain or difficulty passing urine
- Blood in the urine.
Infection or widespread inflammation of the kidney tissue causes impairment of kidney function, and, if severe, it may lead to kidney failure.
Pyelonephritis in Dogs
Pyelonephritis is the medical term used to depict a bacterial infection of one or both kidneys, including the renal pelvis and ureters. In most cases, pyelonephritis results from a bladder infection that has traveled up the ureters. A blockage in the ureter or a congenital malformation of the urinary tract increases the risk of infection.
Pyelonephritis may be acute or chronic. The acute form of pyelonephritis develops suddenly. It is clinically manifested with:
- Loss of appetite
- Severe pain in the lower back (hunched-up posture).
The chronic form develops if an episode of acute pyelonephritis is left untreated. Rarely, it may develop gradually without previous acute infection. The signs develop over months or years and include:
- Loss of appetite
- Weight loss
- Excessive urination
- Excessive thirst.
Microscopic examination of the urine reveals masses of white blood cells. An ultrasound scan may show an enlarged kidney or dilated renal pelvis. Kidney infections are difficult to eliminate and relapses are quite common. Pyelonephritis is usually treated with antibiotics for six to eight weeks. The urine is examined again during and after treatment to confirm that the antibiotics are effective and to prevent recurrence.
Glomerulonephritis in Dogs
If a dog’s immune system is activated, the protein products of that immune activation can literally plug up the filtration channels in the kidney’s individual nephrons and glomeruli. This condition is known as glomerular disease or glomerulonephritis. More often than not, glomerulonephritis leads to chronic kidney failure.
Glomerular disease may be triggered by a chronic bacterial infection, including infection of the prostate gland, septicemia, inflammatory bowel disease, liver inflammation, tick-transmitted diseases and immune-mediated diseases.
If the filtration in the nephrons is blocked, increased blood pressure is likely to develop. The early clinical signs of glomerulonephritis include:
- Those of the underlying cause
- Loss of appetite
- Weight loss
- Decreased muscle mass
- Swelling of the limbs
- Increased thirst
- Hypertension-induced detachment of the retina followed by blindness
Glomerulonephritis invariably causes a chronic loss of protein into the urine (a condition called proteinuria). Consistently positive urinalysis results for protein, in the absence of crystalline sediment (the other important cause of proteinuria), strongly suggests this disease. The vet will probably look for white blood cell casts in the urine, indicating immune system activation, and also measure the ratio of protein to creatinine in the urine to assess kidney function.
If possible, the underlying cause of immune stimulation should be eliminated. Omega-3 polyunsaturated fatty acid supplements help to reduce hypertension. Sodium intake should be reduced to control hypertension. Specialized veterinary diets formulated for dogs with early kidney failure are beneficial.
The Importance of Seeing the Vet
Consult your vet if you notice a marked or persistent change in your dog’s urinary habits. Take a fresh sample of urine that your dog has passed that day to the vet. Collect this from the dog’s midstream flow (a few seconds after it starts urinating).
If possible, use a clean container (such as a jar). Be ready to answer questions about the frequency of urination, any incontinence, the typical amount of water drunk in a day and whether your dog eats wet or dry food.
About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.
She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.
Ivana’s research has been published in international journals, and she regularly attends international veterinary conferences.