JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

January 2024

U-P08

 

Signalment (NADC WCS 2-03): Pig, age and gender unspecified

 

HISTORY: Unknown

 

HISTOPATHOLOGIC DESCRIPTION: Ureter and adjacent fibroadipose tissue: The periureteral connective tissue is expanded by multifocal to coalescing granulomas which are up to 1 cm in diameter and contain a tangential section of an adult nematode surrounded by a central area of proteinaceous fluid and abundant granular, eosinophilic cellular and karyorrhectic debris (lytic necrosis) admixed with abundant viable and necrotic eosinophils, fewer lymphocytes, plasma cells, neutrophils, and hemosiderin-laden macrophages. The inflammation and necrosis are further surrounded by granulation tissue and fibrosis. The sections of adult nematodes are 1 x 3 mm with a thick smooth cuticle, platymyarian-meromyarian musculature, large vacuolated lateral cords, a pseudocoelom, a large intestinal tract lined by few multinucleate cells with a dense tall microvillous brush border (strongyle intestine), and a reproductive tract containing 60 x 70 µm elliptical morulated thin shelled eggs. The parasite intestinal lumen contains degenerate eosinophils mixed with cellular debris. Diffusely there is mild congestion, occasional hemorrhage, and mild dilation of lymphatics.

 

MORPHOLOGIC DIAGNOSIS: Periureteral fibroadipose tissue: Granulomas, eosinophilic, multiple, with adult strongylid nematodes, breed not specified, porcine.

 

ETIOLOGIC DIAGNOSIS: Periureteral stephanuriasis

 

CAUSE: Stephanurus dentatus

 

CONDITION: Kidney worm of swine

 

GENERAL DISCUSSION: 

• Large strongyle, found primarily in porcine perirenal adipose tissue
  1. Recent report describes parasitic encephalitis caused by S. dentatus larvae in the cerebellum (Gustavo et al., 2021)
• Widely distributed in tropical and subtropical countries, including southern USA          
• Most common in pigs raised on soil in wooded areas; eggs and infective larvae are vulnerable to direct sunlight, desiccation and cold temperatures (< 50 F) 
• Hepatic scarring caused by S. dentatus is a common reason for liver condemnation at slaughter; up to 95% of liver condemnations in southeastern USA are due to the kidney worm and ascarids
• Carcass condemnations and production losses due to marked reduction in growth rate and feed efficiency result in great economic impact

 

LIFE CYCLE: 

• Eggs passed in the urine; larvae hatch in 1-3 days
• Molt to infective L3 stage within 3-5 days; in optimum conditions, L3 may survive for 3-5 months in the environment
• Three routes of infection:
  • Ingestion of L3 larvae > wall of intestine 
  • Skin penetration (L3) > systemic circulation > lungs > tracheal migration > wall of intestine 
  • Transplacental infection has been reported
• Earthworms may serve as transport hosts
• From intestine > mesenteric lymph nodes (molt to L4) > portal circulation and mesenteric lymphatics > liver
• After widespread migration, L5 leave liver after 2-4 months > extensive peritoneal cavity migration > adults encyst in perirenal and mesenteric fat which causes necrosis, fibrosis, encapsulation and abscess formation that results in considerable tissue damage
• Patency is uncommon before 9-12 months
• Mature female may lay eggs for 3 years or longer; egg output of an infected pig can exceed a million per day

 

TYPICAL CLINICAL FINDINGS:

• Poor growth despite good appetite; emaciation and ascites in severe cases
• Death may occur following secondary infection, extensive tissue necrosis and urinary obstruction; in heavy infections, death may occur due to peritonitis and intestinal intussusception
• Posterior paralysis is an occasional finding associated with larval migration through the vertebral canal and spinal cord; pain and stiff gait associated with involvement of the psoas muscles
• Persistent eosinophilia

 

TYPICAL GROSS FINDINGS: 

• Adults—Large and stout, 2-5 cm long, 2 mm diameter
• Located in cysts within the perirenal fat that communicate with the renal pelvis and ureters; often present within eosinophilic granulomas in the abdominal cavity
• Enlarged, hard, pale liver with accentuated lobular pattern due to extensive perilobular fibrosis; irregular, white tracks and abscesses in parenchyma; small craters in capsule where larvae have emerged; hemorrhage, peritonitis and perihepatitis in areas of migration from liver to kidney
• Swollen, edematous mesenteric lymph nodes; peritoneal and pleural adhesions
• Renal infarction and scarring with edema in the perirenal adipose and retroperitoneal tissue
• May be seen in some ectopic sites: Pancreas, lumbar muscles, spinal cord, meninges, lungs, myocardium, spleen
• Portal phlebitis with thrombosis in some pigs

 

TYPICAL CYTOLOGIC FINDINGS:

• Eggs found in urine 9-16 months after infection, persist for 3 years or longer
• Vertical transmission in utero possible
• Typically, the last urine voided yields the highest concentration of eggs
• Eggs are large (70 x 120 mm), ellipsoidal, thin shelled, and morulated

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Typical strongylid nematodes: Thin, smooth cuticle; platymyarian-meromyarian somatic musculature; few, large, multinucleate intestinal epithelial cells with a high microvillous border; pseudocoelomic body cavity with a single layer of muscle cells attached to the body wall; internal vacuolated lateral cords
• Eggs: Ellipsoidal, thin‑shelled, morulated, 70x120 um
• Eosinophilic granulomas often containing encysted larvae found in perirenal fat and various organs, especially the pancreas, also liver and lung
• Hepatic perilobular fibrosis and occasionally portal phlebitis with thrombosis

 

ADDITIONAL DIAGNOSTIC TESTS: 

• Urinalysis: May detect presence of embryonated eggs in sediment
• ELISA; detection as early as 2 weeks post-infection

 

DIFFERENTIAL DIAGNOSIS:

• Retroperitoneal lesions: Milder lesions may resemble perirenal edema (U-T13) produced by pigweed (Amaranthus retroflexus), acute oak toxicity, aflatoxins or ochratoxins
• Milk spots in the liver: 
  • Ascaris suum: Liver migration results in similar but less severe lesions; larvae have lateral alae
  • Hepatic tuberculosis: Although they have softer texture, later lesions of Mycobacterium avium hepatitis resemble the gross lesions of parasitic hepatitis

 

COMPARATIVE PATHOLOGY: 

• Dioctophyma renale (U-P09) (aphasmid nematode, giant kidney worm) resides in the renal pelvis and can be up to 100 cm long; definitive hosts are wild fish-eating carnivores, especially mink; also found in dogs, cats, and humans
• Eustrongylides ignotus (aphasmid nematode) causes verminous peritonitis in water wading birds with raised tunnels on abdominal organs (intestines, ventriculus, proventriculus); may have a fibrinous peritonitis with formation of granulomas

 

REFERENCES:

1. Bowman DD. In: Bowman DD, ed. Georgis’ Parasitology for Veterinarians. 10th ed. St. Louis, MO: Saunders Elsevier; 2014:177-178.
2. Brewer MT, Greve JH. Internal parasites: helminths. 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; 2019:1037.
3. Cantile C, Youssef S. Nervous system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, Vol 1, 6th ed. Philadelphia, PA: Elsevier; 2016:391.
4. Cianciolo RE, Mohr FC. Urinary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, Vol 2, 6th ed. St. Louis, MO: Elsevier;2016:442.
5. Cole, RA. Eustrongylidosis. In: Friend M, Franson JC, Cigavonich EA. eds. Field Manual of Wildlife Diseases, General Field Procedures and Diseases of Birds. Madison, WI: U.S. Geological Survey;1999:223-225.
6. Constable PD, Hinchcliff KW, Done SH, Grünberg W. Veterinary Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses. 11th ed. London, England, UK: WB Saunders Company LTD; 2017:1134-1135.
7. Cullen JM, Stalker MJ. Liver and biliary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016:319.
8. Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, D.C.: Armed Forces Institute of Pathology; 1999:8,13,21,24.
9. Gustavo R, Gardiner CH, Oliveira A, et al. Parasitic encephalitis caused by Stephanurus dentatus in a pig in Brazil. J Vet Diagn Invest. 2021;33(5):949-951.
10. Sula, MM and Lane, LV. The urinary system. In: Zachary JF, McGavin MD, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:749. 
11. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, Vol 2, 6th ed. St. Louis, MO: Elsevier; 2016:255.

Click the slide to view.

---