Causes of Canine Urinary Tract Infection
Urinary tract infections (UTIs) are very common in companion dogs, especially in females. Almost all of these infections are caused by bacteria. The infective organisms usually enter the dog’s urinary tract through the urethra and work their way up into the urinary bladder, where they lodge and start to proliferate. Sometimes, the bacterial invaders continue to move up the urinary tract, passing from the bladder through the ureters and setting up camp in the kidneys. There are a few other causes of urinary tract infections in dogs, but they are much less common than bacterial infection.
Bacterial UTIs – The bacteria that infect a dog’s urinary tract can come from the environment, or they can come from the dog’s own fecal matter as it exits the digestive tract. Either way, bacteria typically enter the urinary tract through the urethra, which is the tube-like structure leading from the urinary bladder to the outside world. Bacterial infection of the bladder is called cystitis. Bacterial infection of the kidneys is called pyelonephritis, of the prostate is called prostatitis and of the urethra is called urethritis. Occasionally, bacteria circulating in the bloodstream will lodge somewhere in the urinary tract and cause infection. The most common bacterial culprits of UTIs in dogs are Escherichia coli, Staphylococcus, Proteus, Enterococcus, Klebsiella, Streptococcus, Enterobacter, Chlamydia and Pseudomonas. Interstitial nephritis is a kidney infection triggered by bacterial organisms, most often by Leptospira interrogans. Most bacterial UTIs in dogs are caused by only one bacterial species. Occasionally, multiple species are involved.
Non-Bacterial UTIs – Sometimes, organisms other than bacteria cause UTIs in a dog’s bladder, kidneys or elsewhere. These include: fungi (Candida, Cryptococcus neoformans, Trichosporon, Rhodotorula, others), mycoplasma, viruses, algae and parasitic worms. Capillaria plica are small worms that can infect a dog’s bladder and, less frequently, its ureters and kidneys; dogs become infected by eating earthworms carrying the parasite’s larvae. Giant kidney worms, Dioctophyma renale, can infect a dog’s kidneys but are uncommon in pet dogs; dogs become infected by eating infected raw frogs, fish or earthworms.
Preventing Urinary Tract Infection
The best way to prevent UTIs is to correct whatever predisposes the dog to developing them. If that isn’t possible, affected animals may need to be on long-term, low dose prophylactic antibiotic treatment. This preventative measure carries its own risks, including development of antibiotic resistance. Free access to fresh water is important to help flush microorganisms out of the urinary tract. Regular urination is also critical to reduce the accumulation, reproduction and concentration of bacteria and other infective organisms.
Because so many dogs with UTIs show no symptoms, owners must rely on veterinary protocols for accurate diagnosis. We cannot overemphasize the importance of regular veterinary examinations, including standard blood tests and urinalyses, to identify the many urinary tract infections that would otherwise go undiagnosed. Chronic UTIs can damage the lining and deeper tissues of the urinary tract and become much more difficult to treat with the passage of time.