JPC SYSTEMIC PATHOLOGY
Signalment (NADC WCS 2-03): Pig, age and gender unspecified
HISTOPATHOLOGIC DESCRIPTION: Ureter and adjacent fibroadipose tissue: The periureteral connective tissue is expanded by multifocal to coalescing, up to 1 cm diameter granulomas that 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 degenerate eosinophils, fewer lymphocytes, plasma cells, neutrophils, and hemosiderin-laden macrophages. The inflammation and necrosis is 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, 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 micron 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
- Large strongyle, found primarily in porcine perirenal adipose tissue
- 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 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
- 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 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
- Retroperitoneal lesions: Milder lesions may resemble perirenal edema 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
- Dioctophyma renale (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
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