Urinary Tract Infections
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Urinary tract infections, or UTIs, are most commonly infections of the urinary bladder with bacteria, but could also include infections of the kidney, ureters, or urethra. Although uncommon, fungi and viruses can also infect the urinary tract. Bacterial infections of the urinary bladder are also called "bacterial cystitis." It has been estimated that 14% of dogs will have a urinary tract infection sometime during their lives.

What are the parts of the urinary tract?

The urinary system is responsible for filtering wastes from the blood and both forming and secreting urine. These functions help to maintain the composition and volume of body fluids. Although it has far-reaching effects, the urinary tract is relatively simple anatomically and consists of:

  • Kidneys
  • Ureters (tubes allowing flow of urine from the kidney to the bladder)
  • Bladder
  • Urethra (tube allowing flow of urine from the bladder to the outside of the dog)

The main organs are the kidneys, which filter blood and produce urine. The other parts are simply accessory structures for the transport and storage of urine.

What causes urinary tract infections?

The urinary bladder is normally sterile, meaning there are no bacteria present. Most urinary tract infections are the result of bacteria entering the urethra and then traveling up to the bladder, or even further up to the kidneys. Normally the body's defense mechanisms prevent bacteria or other organisms from moving up the urinary tract and growing there.

What are the risk factors for urinary tract infections?

Certain diseases can predispose a dog to develop urinary tract infections. These include hyperadrenocorticism (Cushing's disease), diabetes mellitus, kidney failure, and bladder cancer. Conditions that change the normal anatomy of the genital area, such as swelling of the vulva, can increase the risk of urinary tract infections. If a dog has bladder stones, the risk of recurring UTIs is increased. Dogs on high long-term doses of corticosteroids (eg., prednisone) may also be at increased risk.

What are the symptoms of urinary tract infections?

Some dogs with a urinary tract infection may not show any signs of disease. Others may show one or more of the following:

  • Urinating small amounts frequently (poillakiuria)
  • Painful urination (dysuria)
  • Blood in the urine (hematuria)
  • "Accidents"

Other diseases that can cause similar signs in dogs include bladder stones, bladder cancer, and prostatitis. Bladder infections generally do not cause fever or other general signs of disease. Infections of the kidney, however, can cause fever, pain, loss of appetite, depression, and other more severe symptoms.

How is a urinary tract infection diagnosed?

A veterinarian would suspect a urinary tract infection if the dog was showing the symptoms listed above. A urine sample would generally be taken by cystocentesis and submitted to a laboratory for culture and sensitivity. In addition a urinalysis would be performed on the urine sample.

How is a bacterial urinary tract infection treated?

Based on the culture and sensitivity, the appropriate antibiotic would be prescribed. Even if the symptoms resolve, it is important to give the entire course of antibiotics.

Why do some urinary tract infections recur?

In some instances, a urinary tract infection may recur or not respond well to antibiotics. This can occur for several reasons

  • the bacteria are resistant to (not killed by) the antibiotic that was chosen
  • the entire dosage regimen was not given
  • an underlying condition exists, such as bladder stones or bladder cancer, which provides a "hiding place" for the bacteria
  • another disease is present, such as diabetes mellitus, or the immune system is suppressed

In these cases the culture and sensitivity help to determine if the same type of bacteria is causing the infection or if there is infection with different types. Additional tests, such as radiographs (x-rays), a chemistry panel, and a complete blood count, may need to be performed to help determine why the infection is not responding to treatment or is recurring.

References and Further Reading

Labato, MA. Uncomplicated urinary tract infection. In Bonagura, JD; Twedt, DC (eds) Kirk's Current Veterinary Therapy XIV. Saunders, St. Louis MO, 2009.

Barsanti, JA. Multidrug-resistant urinary tract infection. In Bonagura, JD; Twedt, DC (eds) Kirk's Current Veterinary Therapy XIV. Saunders, St. Louis MO, 2009.

Bartges, JW. Urinary tract infections. In Ettinger, SJ; Feldman, EC (eds). Textbook of Veterinary Internal Medicine. Elsevier, St. Louis, MO, 2005.

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