JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

November 2023

U-B07 (NP)

 

Signalment (JPC Accession # 1712745): A 6-month-old gilt

 

HISTORY: A recently bred, 6-month-old gilt exhibited hematuria for 3 or 4 days before death. Necropsy findings included pyelonephritis, hemorrhagic ureteritis, and mucohemorrhagic cystitis.

 

HISTOPATHOLOGIC DESCRIPTION: Urinary bladder: Diffusely, mucosal epithelium forms hyperplastic papillary projections with multifocal areas of erosion. Remaining mucosal epithelial cells are mildly to moderately expanded by homogenous amphophilic and fibrillar material or variably sized clear vacuoles that peripheralize nuclei (mucinous metaplasia) or pile up to 8 cells thick (hyperplasia). Multifocally within the mucosa there are small aggregates of neutrophils (microabcesses) and cellular and karyorrhectic debris (necrosis). Diffusely, the lamina propria is moderately expanded by moderate numbers of lymphocytes, plasma cells, macrophages that occasionally contain intracytoplasmic brown pigment (hemosiderin), congestion, and hemorrhage, fibrin, and edema. The urinary bladder muscular tunics are mildly expanded by increased fibrous connective tissue (fibrosis) and clear space with ectatic lymphatics (edema).

 

MORPHOLOGIC DIAGNOSIS: Urinary bladder: Cystitis, chronic-active, neutrophilic and lymphohistiocytic, diffuse, mild with epithelial hypertrophy, mucinous metaplasia, and microabscesses, pig, breed not specified, porcine.

 

ETIOLOGIC DIAGNOSIS: Bacterial cystitis

 

CONDITION: Porcine cystitis and pyelonephritis

 

CAUSE: Actinobaculum suis (previously Eubacterium suis, Corynebacterium suis)

 

GENERAL DISCUSSION:

• A. suis is a gram-positive, obligate anaerobe, non-motile, non-spore forming, urease producing, pleomorphic (“coryneform”) bacillus (2-3 um long and 0.3-0.5 um wide)
• A. suis is a normal inhabitant of the prepuce and can be isolated from the preputial diverticulum of most male pigs over ten weeks of age; it rarely causes clinical disease in males
• Primary cause of cystitis and pyelonephritis in swine; one of the leading causes of death in sows
• In breeding sows, A. suis causes peracute to chronic hemorrhagic cystitis, ureteritis, and pyelonephritis 
• Predisposing factors:
  • Mating (usually occurs within 1-4 weeks of mating)
  • Trauma to urogenital tract of female
  • Other organisms (E. coli, streptococci and Proteus spp) may damage bladder epithelium to allow A. suis to adhere to mucosa and grow; it is rare to have a pure infection of A. suis  
  • Water restriction, crystalluria, intensive confinement conditions

 

PATHOGENESIS:

• Venereal disease: Venereal transmission is believed to be the primary, if not sole, method of infection of the sow; boars become infected through close contact with other infected animals or contaminated pens and transmit the bacteria to sows or gilts at breeding
• The initial infection occurs in the vagina; during estrus, estrogen causes the normally slightly acidic environment to become more alkaline providing conditions favorable for growth of the organism
• A. suis is urease (+) > breaks down urea > ammonium ions liberated > tissue damage and inflammatory reaction
• A. suis are heavily piliated and adhere to and colonize the bladder epithelium > cystitis > damage at the ureterovesical junction > ascending infection > blockage of proximal ureter > hydronephrosis, pyelonephritis
• If obstruction is complete and bilateral there is acute renal failure and sudden death; if blockage is partial chronic renal failure results

 

TYPICAL CLINICAL FINDINGS:

• Acute phase: Sudden death with or without clinical signs, hematuria, azotemia, mild fever, anorexia, painful urination, arching of back, polyuria, and polydipsia and weight loss as disease progresses 
• Sows develop chronic renal failure with progressive weight loss if they survive the acute infection
• Urinalysis - Increased turbidity, pyuria, macrohematuria, bacteriuria, proteinuria, alkaline urine (pH > 8.5) due to ammonia produced by bacterial urease

 

TYPICAL GROSS FINDINGS:

• Limited to the urinary tract
• Acute:
  • Bladder wall is swollen, edematous, and hyperemic and may be covered with gritty, mucinous material
  • Kidneys: Yellow areas of degeneration on the surface extending into the parenchyma
    • Pelvis: dilation with mucoid fluid and flakes of necrotic debris
    • Medullary pyramids: dark foci of necrosis
• Chronic:
  • Ulcerative and erosive lesions in the bladder wall; +/- pus
  • Thick-walled ureters
  • Obvious pyelonephritis 

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Urinary bladder - Submucosal edema and fibrosis; degeneration and necrosis of epithelium; hemorrhage; pseudomembrane formation; Gram (+) diphtheroid bacteria in exudate or necrotic epithelium
• Kidneys - Acute, purulent to chronic interstitial nephritis, pyelitis, or pyelonephritis with fibrosis of medulla and pelvis; necrosis of renal papillae; bacterial colonies in exudate

 

ADDITIONAL DIAGNOSTIC TESTS:

• Gram stain (positive)
• Culture - blood agar or Columbia CNA agar (selective medium for isolation of A. suis)
• Immunofluorescence

 

DIFFERENTIAL DIAGNOSIS (for Bacterial Cystitis):

 

COMPARATIVE PATHOLOGY:

• Pathogenic Corynebacteriae
  • Humans - Corynebacterium diphtheriae - diphtheria
  • Cattle - C. renale - pyelonephritis, ureteritis, cystitis; C. cystitidis - hemorrhagic cystitis and pyelonephritis; C. pilosum - cystitis and pyelonephritis; C. bovis - rare cause of mastitis
  • Sheep and goats - C. pseudotuberculosis - caseous lymphadenitis
  • Horses - C. pseudotuberculosis - ulcerative lymphangitis and pectoral abscesses
  • Rodents - C. kutscheri - pseudotuberculosis
  • Many species - C. ulcerans - wound infections and abscesses

 

REFERENCES:

1. Broes A, Taylor DJ, Martineau GP. Miscellaneous bacterial infections. In: Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds., Diseases of Swine. 11th ed., Hoboken, NJ: John Wiley and Sons; 2019:981-982.
2. Cianciolo RE, Mohr FC. Urinary System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, Vol. 2, 6^th Ed. St. Louis, MO: Elsevier. 2016: 439, 459.
3. Constable PD, Hinchcliff KW, Done SH, Grunberg W. Veterinary Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses. 11th ed. Saint Louis, MO: Elsevier; 2017:1132-1134.
4. Nagaraja TG. Corynebacterium. In: McVey DS, Kennedy M, Chenappa MM, eds. Veterinary Microbiology, 3^rd Ed. Ames, IA: Elsevier. 2013:217. 
5. Sula, MM and Lane, LV. The urinary system. In: Zachary JF, McGavin MD, eds. Pathologic Basis of Veterinary Disease. 7^th ed. St. Louis, MO: Elsevier; 2022:669. 
6. Woldemeskel M, Drommer W, Wendt M. Microscopic and ultrastructural lesions of the ureter and renal pelvis in sows with regard to Actinobaculum suis infection. Jour Vet Med Assoc Physiol Pathol Clin Med. 2002; 49:348-352.

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