Porcine cystitis-pyelonephritis complex, a leading cause of mortality in sows, has been reported throughout the world. Increased incidence appears to be correlated with changes in management, particularly the adoption of confinement housing for gestating sows. Distinguishing features of endemic cystitis and pyelonephritis within a herd include lack of a temporal relationship between the vulvar discharge and the estrous cycle, minimal effect on herd fertility, low morbidity, high mortality, and an increased frequency in advanced-parity (6+) sows.
Etiology and Pathogenesis
A wide variety of bacteria has been isolated from cases of porcine cystitis and pyelonephritis, including Escherichia coli, Arcanobacterium pyogenes, and Streptococcus and Staphylococcus spp. These endogenous and opportunistic organisms typically inhabit the lower urinary tract and are often referred to as being responsible for nonspecific urinary tract infections. Actinobaculum suis, a specific urinary pathogen, is an important cause of ascending infection in swine. Formerly classified in the genera Eubacterium and Actinomyces, A suis is a gram-positive rod-shaped bacterium that grows well under anaerobic conditions and is a commensal organism of the porcine urogenital tract. A suis is fimbriated, and the short, wide urethra of the sow enhances accessibility to the bladder.
Once within the bladder lumen, the alkalinity of the environment increases due to the cleavage of urea into ammonia via the urease enzyme. The elevated pH enhances bacterial proliferation and inflames the mucosal surface. The alkaline environment also inhibits the growth of competitive microflora and promotes the precipitation of urinary salts and crystals, particularly struvite. Such precipitates not only further increase inflammatory changes in the bladder mucosa but also provide a nidus for bacterial growth and protection from antibiotics and host defense mechanisms. While the primary means for accessibility to the kidneys is not yet completely understood, it is hypothesized that damage to the ureteric valves secondary to bacterial products (possibly originating from E coli) may predispose affected animals to pyelonephritis.
Problems frequently encountered in confinement facilities that hasten the development of porcine cystitis are the reduced availability of water, increased fecal contamination of the perineal area, excessive weight gain, and leg injuries, all of which result in a reduction in the frequency of urination and enhanced bacterial survival in the urogenital tract. A suis has been isolated from the preputial cavity of boars at slaughter, the vaginal tract of neonatal piglets sampled immediately following parturition, and the vaginal tract of sows sampled throughout all stages of production. It may also be isolated from voided urine, contaminated parturition sleeves of farrowing attendants, pen floors of farrowing and nursery rooms, and the boots of stockpersons working in the breeding area. The sole route of transmission was believed to be copulation, but it is now understood that the organism is ubiquitous, and the vaginal tract can become colonized at anytime during the life of the pig.
Clinical signs vary according to the severity and the phase of the disease. In acute and severe cases, affected animals may be found dead, probably from acute renal failure. Symptomatic animals are usually afebrile and may show anorexia, hematuria, and pyuria. The urine is typically reddish brown with a strong odor of ammonia. Urinary pH may increase from normal values of 5.5–7.5 up to 8–9. Animals that survive the initial infection frequently experience weight loss and reduced productivity secondary to end-stage renal disease, resulting in premature removal from the breeding herd. Inflammatory reaction on the mucosal surface of the bladder may be catarrhal, hemorrhagic, purulent, or necrotic, and the bladder wall may be thickened. Struvites can also be found in the lumen. The ureters, often filled with exudate, may increase to as much as 2.5 cm in diameter. Unilateral or bilateral pyelonephritis or pyelitis is the primary lesion in the kidneys. The pelvic region of the kidney, which is frequently distended with blood, pus, and foul-smelling urine, often shows irregular ulceration and necrosis of the papillae. In longstanding cases of pyelonephritis, fibrosis ultimately replaces inflammation.
Cystitis and pyelonephritis in live animals can best be presumptively diagnosed when frequent micturition of bloodstained and cloudy urine can be observed. Examination of the urine sediments may reveal the presence of inflammatory cells, RBC, granular renal casts, bacteria, and crystals. Due to the striking gross lesions, confirmation of the diagnosis is usually not difficult. To properly isolate the causative organism, care must be taken during sample collection to minimize exposure to oxygen. In the field, the bladder should remain unopened, and the neck of the bladder should be sealed with umbilical tape. Similar care should be taken with renal tissue. Lesions of pyelonephritis can be demonstrated by examination of one kidney; the other should remain unopened with the ureter sealed as previously described. Cultures should be grown on colistin nalidixic acid agar at 37°C under anaerobic conditions for 5–7 days. If the culture is to be done at a distant location, swabs can be placed into Kary Blair anaerobic transport media for shipment.
Treatment and Prevention
Treatment of urinary tract infections may be successful if the correct antibiotic is administered early in the disease course. Penicillin and ampicillin are often the drugs of choice, due to their effectiveness in alkaline conditions and their propensity for excretion through the urinary tract. Dosages of 2.2 mg/kg are typically administered IM for 3 days. Water-soluble ampicillin can be administered at 2.3 mg/kg for 5 days, although bioavailability is questionable and cost may become an issue. Acidification of the urine through oral administration of feed-grade citric acid has been reported. Results showed a reduced incidence of clinical urinary tract disease, as well as highly significant (p <0.0001) differences in urinary pH and bacterial concentration/mL of urine in medicated versus nonmedicated groups. A level of 70 mg of citric acid was administered daily for 14 days with no palatability problems.
Maintaining excellent hygiene during breeding and parturition, as well as throughout the gestation period, is critical for prevention of urinary tract disease. Facilities must be properly designed to reduce the spread of pathogens within the breeding herd and allow for efficient removal of feces from the environment. Free-choice water should be available at all times, as restricting water availability through the use of intermittent delivery systems or poor husbandry results in an increase in abnormal urine parameters in gestating sows, including reduced urine output, elevated specific gravity (>1.026), and increased creatinine concentration. Finally, because a higher degree of urinary tract disease can be seen in older sows, proper culling procedures are important to ensure that an optimal parity distribution is maintained within breeding herds.
Last full review/revision July 2011 by Scott A. Dee, DVM, MS, PhD, DACVM