April 8, 2021 – A sudden puddle on the floor. Drops of blood in urine. Asking to go outside more than usual. Straining. All are signs that a dog might have a urinary tract infection (UTI). These all-too-common infections are distressing for both dogs and their people, but new information on diagnosis, treatment and prevention could make these troublesome infections a lot less common.
Most urinary tract infections diagnosed in dogs and cats involve the bladder and urethra (the structure leading from the bladder that urine passes through as it is expelled). The kidneys and ureters (the tubes that carry urine from each kidney to the bladder) are considered to be part of the upper urinary tract, and although we’ll touch on infection in these structures, the vast majority of urinary tract infections involve only the lower urinary tract structures.
Lower urinary tract infections – the basics
On the surface, it would seem that urinary tract infections are simple – bacteria get into the bladder and cause irritation which in turn leads to clinical signs.
While true in many respects, scientists also are learning that this view is too simplistic, especially when it comes to recurrent infections.
To begin, we need to understand how disease-causing bacteria invade the urinary tract and cause disease.
Bacteria that come from the large intestine and skin are the major culprits responsible for UTIs. Once inside the urinary tract, bacteria are in one of two forms. Either they float freely in the urine (planktonic bacteria) or they raft together to form special communities called biofilms.
The body has several defenses against urinary tract infections. The first is that the force of voiding can expel unwanted bacteria from the urinary tract. Cells that are part of the immune system line the urinary tract and help prevent infections. Lastly, inflammation (but not too much) helps destroy potential invaders.
Planktonic bacteria are more susceptible to bladder defense mechanisms and antimicrobials than biofilms. Biofilms often are associated with structures such as urinary catheters but they also can attach directly to the cells lining the urinary tract. It’s more difficult for the body to eliminate biofilms than planktonic bacteria but it’s possible, and many researchers are studying new ways to disrupt and treat biofilms.
UTI risk factors
Several risk factors for UTIs have been identified in dogs. These include:
- Female sex
- Older age
- Chronic kidney disease
- Urinary tract stones
- Urinary incontinence
- Recent antibiotic use
- Bladder cancer
- An inability to completely empty bladder during voiding
- Body and urinary tract conformation abnormalities
- Immunosuppression (controversial)
There’s a question mark by immunosuppression. Although it seems logical that immunosuppression, for any reason, would be a risk factor for UTIs, the evidence is contradictory. Some studies show a clear link, while others suggest that, although there might be some bacteria in the urine, they’re not causing any clinical signs. Others are concerned that the immunosuppressive medications are simply decreasing inflammation but the bacteria are still a problem. More work needs to be done to sort out whether or not treatment is needed in these patients.
Some conditions previously thought to be risk factors for UTIs have fallen off this list. For example, many veterinarians were taught that dilute urine was a risk factor for UTIs. The thinking behind this was that more concentrated urine was a harsh place for bacteria to thrive. However, very recent work suggests this isn’t the case based on studies in dogs with diabetes and hyperadrenocorticism (Cushing’s Disease), as well as in cats with diseases that cause dilute urine. Again, more work needs to be done to sort out why this might be the case, but this is good news for pet parents who have a dog that suffers from these conditions.
Subclinical bacteriuria – normal…or not?
As our ability to detect urinary tract infections improved, veterinarians frequently began finding bacteria in the urine of dogs who had no signs of infection. Once called “occult UTIs” the term subclinical bacteriuria (SCB) is now used to describe this increasingly common clinical finding.
SCB is not uncommon, with rates of 2.1% to 12% being reported in clinically healthy dogs. Higher rates (15%-74%) have been noted in dogs with concurrent diseases as diverse as parvoviral enteritis to obesity.
For years, veterinarians thought urine was sterile and any bacteria found in a urine sample was abnormal. Recent research has shown the urinary tract actually does have a resident group of microorganisms that are part of the vast complex of bacteria living in and on our bodies.
In addition, the treatment of urinary tract infections in both people and animals is contributing to the growing number of antibiotic-resistant bacteria present in the environment. Some naturally resistant bacteria survive treatment to pass on this trait. Small amounts of antibiotic are excreted into the environment during treatment, also favoring resistant strains.
The current recommendation from veterinary infectious disease experts is dogs with SCB should not be treated with antimicrobial therapy unless they’re pregnant or having an invasive urinary tract procedure performed (such as surgery). Evidence suggests treating SCB can actually increase the risk of UTIs. As always, it’s important for dog owners to work with their family veterinarian to determine what’s best for an individual patient.
Clinical signs, diagnosis and treatment
Although signs of lower UTIs can vary a bit between dogs, the most common ones are:
- Straining to urinate (stranguria)
- Small volume, frequent urinations (pollakiuria)
- Blood in the urine (hematuria)
- Excessive licking of genital area
- Accidents in the house
The same signs can be present if the upper urinary tract is affected, with fever and kidney pain more likely to be noted if the upper urinary tract is involved.
Diagnosis begins with a complete urinalysis, which includes an examination of the urine under a microscope as well as testing for the presence of substances such as protein and glucose. The presence of both white blood cells and bacteria in urine, coupled with clinical signs, is strongly suggestive of a UTI. Culturing the urine usually is performed to find out what type of bacteria are present as well as to learn which antimicrobials will be most effective against the bacteria in the sample.
Treatment is guided both by culture results and patient history. Uncomplicated UTIs are treated with seven days of antibiotics (more on this later). Complicated UTIs can require additional testing and longer antibiotic therapy (four weeks is standard) coupled with close monitoring to ensure that the infection is cleared.
Additional therapies can include pain medication and adequate control or treatment of any underlying conditions.
Strict treatment compliance by the pet owner also is an important component of any therapy. It’s often tempting to stop treatment when clinical signs resolve but it’s important to complete any course of antimicrobial therapy as directed to avoid relapses. Incomplete antibiotic therapy is another factor contributing to the development of antimicrobial resistance.
Working to find new information and treatment for UTI in dogs
Morris Animal Foundation has invested just over $500,000 in several studies looking at all aspects of UTIs in dogs, especially new treatment options.
Current studies include the use of a biotherapeutic product that’s instilled into the bladder. Researchers are comparing this product to standard antibiotic therapy. If successful, this product could be used instead of antimicrobials to treat UTIs.
One newly funded project is studying whether a three-day course of the antibiotic amoxicillin is as effective as the standard seven-day treatment protocol. If the three-day regimen is effective, this would help not only owner compliance, but also help to limit antimicrobial resistance by decreasing the amount of antibiotic entering the environment.
Another study looking at how bacteria in the urine work together to improve their survival rates in the harsh environment of the urinary tract could help veterinarians do a better job eliminating infections when multiple bacteria are present.
The Golden Retriever Lifetime Study also has provided some interesting data on the frequency of urinary tract infections occurring in the cohort.
As of March 2021, 507 dogs in the Study (3,044 dogs formed the original cohort) have been diagnosed with at least one urinary tract infection (as coded by the Study veterinarian), 377 females and 130 males, which is consistent with the previous observations that UTIs are more common in females. Urinary tract infections remain one of the most common disease conditions noted by our Study veterinarians and we’ll be watching this trend closely as our cohort continues to age.