Cystitis

Cystitis is usually a secondary problem consequent to alterations in urine flow resulting from an anatomic defect of the bladder or urethra, urolithiasis, bladder neoplasia, bladder paralysis, or use of indwelling bladder catheters. Cystitis can lead to pollakiuria, stranguria, hematuria, pyuria, and incontinence. Scalding and accumulation of urine crystals may be observed on the perineum of mares or around the preputial opening and on the front of the hindlimbs in male horses. These findings should not be confused with normal estrus activity in an occasional mare.

Diagnostic evaluation includes physical and rectal examinations and collection of a urine sample for urinalysis and quantitative bacterial culture. Results of hematology and serum chemistry are usually normal. In the absence of uroliths or other bladder masses, transrectal palpation of the bladder is usually within normal limits; however, endoscopic examination of the bladder may be helpful in assessing mucosal damage in horses with cystitis. Because normal equine urine is rich in crystals and mucus, gross inspection of urine may be unrewarding, but sediment examination may reveal a high number of white blood cells (>10 per high-power field) and the presence of bacteria in some horses with cystitis. In fact, normal sediment examination results do not rule out UTI, and definitive diagnosis requires quantitative culture results of more than 10,000 colony-forming units (cfu)/mL in a urine sample collected by midstream catch or bladder catheterization. For best results, urine sediment should be evaluated within 30 to 60 minutes of collection, and samples for culture should be cooled during transport because bacterial numbers may increase in samples left at room temperature. Organisms that may be recovered on culture include Escherichia coli, Proteus mirabilis, Klebsiella spp, Enterobacter spp, Streptococcus spp, Staphylococcus spp, Pseudomonas aeruginosa, and Corynebacterium renale. Isolation of more than one organism is not uncommon, and UTI with Enterococcus spp is a common complication when indwelling bladder catheters are used for more than several days. Candida albicans infections of the lower urinary tract have developed in sick neonatal foals receiving broad-spectrum antimicrobials for treatment of sepsis. Equine rhinitis A virus can be detected in high numbers in urine of horses affected with respiratory disease, but clinical signs of cystitis have not been recognized with this infection.

Treatment of cystitis requires correction of anatomic defects or urolithiasis and administration of systemic antimicrobials and nonsteroidal antiinflammatory drugs (NSAIDs). While urine culture results are pending, a trimethoprim-sulfonamide combination, a tetracycline (oxytetracycline or doxycycline), ceftiofur, ampicillin, or the combination of penicillin and an aminoglycoside can be an initial choice for a treatment duration ranging from 3 to 7 days. The route of metabolism of the antimicrobial should be another consideration. For example, sulfamethoxazole is largely metabolized to inactive products before urinary excretion, whereas sulfadiazine is excreted largely unchanged in urine. One to three days of NSAID administration usually provides effective analgesia for cystitis. However, when dysuria persists in the face of NSAIDs, administration of phenazopyridine (4 mg/kg, PO, every 8 to 12 hours) may alleviate lower urinary tract pain in these patients. In humans, phenazopyridine relieves burning, irritation, and discomfort as well as urgent and frequent urination caused by UTIs. The medication acts as a topical local anesthetic on ureteral, bladder, and urethral mucosa, but does not have antimicrobial activity. Also, clients should be informed that the medication will turn urine an orange color that can stain hands and clothing. Efficacy of the drug should be apparent after the first or second dose, and it is typically administered for only 2 to 3 days. Additional management of UTIs can include allowing pasture access, daily supplementation with 50 to 75 g of loose salt, or provision of warm water during cold weather in an attempt to increase water intake and urine production.

Persistent UTIs require longer treatment (weeks to months), and antimicrobial selection should be based on susceptibility testing results for isolated pathogens (route of administration and cost are additional considerations). It warrants mention that resistance to a particular antimicrobial agent in vitro may not preclude successful treatment with the drug in vivo because of the higher concentrations achieved in urine. Laboratory reports provide minimal inhibitory concentration (MIC) data for serum, not urine, antimicrobial concentrations. To determine whether a particular bacterial isolate in urine may be susceptible to urine concentrations of a drug, the actual MIC for some organisms can be determined by the laboratory when specifically requested. Similarly, demonstrable susceptibility in vitro does not always guarantee a successful response to treatment. For example, Enterococcus spp are common isolates with indwelling bladder catheters, and although they are routinely found to be susceptible to potentiated sulfonamide combinations in vitro, this pathogen is inherently resistant to these combinations in vivo. Rather, removal of the bladder catheter is often essential for resolution of these UTIs. Ideally, midstream urine sample (voided or collected by catheterization) should be submitted for bacterial culture 1 week after treatment of a persistent lower UTI has been discontinued.

Encrusting Cystitis

An occasional horse, male or female, may develop severe encrusting cystitis in association with ascending infections with Arcanobacterium spp or Trueperella spp (previously Corynebacterium spp). Some affected horses are otherwise healthy but have moderate to severe dysuria and incontinence, whereas others have concurrent bladder paresis as a predisposing cause for the ascending UTI. These infections appear to be similar to UTIs in humans and small animals with Corynebacterium urealyticum. This organism is capable of splitting urea into ammonium ions, and an alkaline urine pH is important for persistence of the UTI. Affected humans and animals often develop a peel of calcified, purulent uromucoid debris that adheres to the underlying, markedly irritated bladder mucosa, leading to the term encrusting cystitis. Why certain patients develop these severe UTIs remains incompletely understood, although previous urologic procedures or renal transplantation (and concurrent immunosuppressive therapy) appear to be risk factors in humans. The author has managed a few horses with encrusting cystitis for several years using intermittent bladder lavage and debridement in combination with long-term antimicrobial treatment and intermittent NSAID use. Although clinical signs have improved, resolution of the UTI has not been accomplished.