Definition
Adherence and replication of bacteria within the urinary bladder.
Pathophysiology
Urinary tract defenses against bacterial infection include anatomic and functional barriers that prevent retrograde urethral ascent of pathogens, the inherent antibacterial properties of normal urine, and local (i.e., mucosal) and systemic immune responses. Bacterial colonization and persistence within urine or on urothelial surfaces requires impairment of one or more of these defense mechanisms. The mucosal inflammatory response promotes leukocyte infiltration into the bladder wall, resulting in dysuria, pollakiuria, and hematuria.
Systems Affected
Renal/Urologic
Incidence/Prevalence
- Prevalence of UTIs in animals with predisposing conditions is more clinically relevant than total population frequencies.
- Prevalence of UTIs in dogs:
- Without urinary tract-associated clinical signs: 2.1%
- With diabetes mellitus, at initial diagnosis: 7.7%
- With diabetes mellitus, at any point in time: 37%
- With hyperadrenocorticism, at initial diagnosis: 46%
- With thoracolumbar intervertebral disc extrusion: 20.0–38.5%
- With indwelling urinary catheters while hospitalized: 63.8%
- Prevalence of UTIs in cats:
- Without lower urinary tract-associated clinical signs: 0.9%
- With lower urinary tract-associated clinical signs: 3.4–12.0%
- With ureteral calculi: 8.4%
- With chronic kidney disease, at any point following diagnosis: 16.9–29.1%
- With diabetes mellitus, at any point following diagnosis: 12.2–12.8%
- With uncontrolled hyperthyroidism, referred for I131 treatment: 12.2%
- With perineal urethrostomies, at any point following surgery: 22%.
Signalment
Species
More common in dogs than cats
Breed Predilections
None
Mean Age and Range
- UTIs may occur in any age animal.
- Male dogs: mean, 8.0 ± 0.1 years; female dogs 7.7 ± 0.1 years. Relative risk of UTI diagnosis increases with age.
- Cats: Median, 7.7 yrs (range, 0.2–17 years).
Predominant Sex
- Dogs: female dogs more commonly affected than male dogs.
- Cats: male and female cats affected in approximately equal numbers.
Signs
Historical Findings
- Patients may be asymptomatic.
- May have variable severity of:
- Pollakiuria, dysuria, hematuria, stranguria, urgent need to urinate (which may progress to urinary incontinence), urinating in inappropriate locations, and excessive licking at or discharge from the genitalia.
- Systemic clinical signs (anorexia, generalized discomfort) occur infrequently.
Physical Examination Findings
- Unremarkable in most animals.
- Abnormalities occasionally noted with urinary bladder palpation:
- Bladder wall thickening or crepitus
- Stimulation of micturition, regardless of bladder urine volume
- Pain reactions.
Causes
- Commensal skin, mucosal, or gastrointestinal bacteria adhere to the urethral epithelium, and ascend retrograde.
- Urine cultures identify aerobic bacterial species in >99% of UTIs. A single bacterial species is isolated in 75–95% of cases.
- Escherichia coli, Staphylococcus spp., or Proteus spp. are isolated from approximately 50% of animals.
- Eight species of bacteria (E. coli, Staphylococcus, Proteus, Streptococcus, Klebsiella, Enterococcus, Pseudomonas, and Corynebacterium) account for approximately 95% of UTIs.
Risk Factors
- Systemic immune dysfunction (e.g., suppressed immunity in dogs with hyperadrenocorticism).
- Nidus for bacterial adherence and defense mechanism avoidance (e.g., indwelling urinary catheters, uroliths).
- Altered composition of urine (e.g., persistently dilute urine, glucosuria).
- Compromise of barriers that inhibit retrograde bacterial movement (e.g., loss of urethral tone, ectopic ureters, incomplete bladder emptying).
- Disrupted urinary tract mucosal defenses (e.g., urolith-associated mucosal trauma).
