JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
October 2021
D-P29 (NP)

Signalment (JPC #2316934):  Young adult male cynomolgus monkey (Macaca fasicularis)

HISTORY:  This lesion was an incidental finding at the terminal necropsy of a subacute toxicity study. Gross finding was a single, 0.5 cm diameter, dark green raised area within the wall of the cecum at necropsy.

HISTOPATHOLOGIC DESCRIPTION:  Large intestine:  Multifocally expanding the submucosa and the tunica muscularis are granulomas that are up to 4 mm in diameter and centered on multiple cross sections of adult Strongyle nematodes admixed with a central core of eosinophilic cellular and karyorhectic debris (lytic necrosis), brown granular hemosiderin, canary yellow angular hematoidin, abundant hemosiderin-laden macrophages, and fewer eosinophils, rimmed by epithelioid macrophages, multinucleated giant cell macrophages, fewer lymphocytes, plasma cells, and eosinophils, further rimmed by a variably thick band of fibrous connective tissue. Inflammatory cells infiltrate multifocally into the tunica muscularis, muscularis mucosa, and lamina propria.  Adult nematodes are 350um in diameter, with a prominent, 2-4 um, smooth, eosinophilic cuticle, platymyarian-meromyarian musculature, vacuolated lateral cords, an intestine lined with few multinucleated cells with a dense microvillar layer, and a reproductive tract. The lamina propria is infiltrated by low numbers of eosinophils and lymphocytes. The intestinal lumen contains cellular debris, plant material, bacilli, colonies of coccobacilli, and occasional free, spherical, 60-75um, ciliated protozoal trophozoites (likely Balantidium coli).

MORPHOLOGIC DIAGNOSIS:  Large intestine, submucosa and tunica muscularis: Granulomas, eosinophilic, chronic, multifocal, moderate, with adult Strongyle nematodes, etiology consistent with Oesophagostomum spp., Macaca fasicularis, non-human primate.

ETIOLOGIC DIAGNOSIS: Colonic oesophagostomiasis

CAUSE:  Oesophagostomum spp

GENERAL DISCUSSION:

• In non-human primates:
  • Common nematode parasite in Old World monkeys and great apes, in the family Strongylidae
  • 4^th stage larvae form pyogranulomatous nodules in the submucosa of the colon; occasionally found in ectopic locations such as the peritoneum, mesentery, and kidney
  • Potentially zoonotic
  • Mild disease except in heavy infectious or if the nodules rupture on the serosal aspect causing peritonitis
  • In nonhuman primates species most frequently mentioned include apiostomum, O. bifurcum, O. aculeatum, O. stephanostumum, and O. blanchardi
• In sheep, cattle, and swine:
  • In sheep, columbianum is important in warm temperate to tropical regions and low burdens can be pathogenic, causing anorexia, mucoid diarrhea, and ill-thrift
  • Nodules similar to those seen in NHPs seen in the large intestine are encysted 4^th stage larvae; adults found within the mucus layer in colon
  • Deeper nodules may project on serosal surface, termed pimply gut
  • In cattle, radiatum causes similar disease with loss of appetite, reduced productive efficiency, anemia, hypoproteinemia, and diarrhea
  • Hemorrhage seen at sites of larval emergence can lead to anemia
  • In swine, disease is usually subclinical

LIFE CYCLE:

• Direct life cycle: Life cycle of Oesophagostomum begins with the passing of eggs in the animal feces >eggs develop into stage one larvae > molts twice (approximately one week to become infectious stage three larvae) > host ingests stage three larvae > migrate to intestine, unsheath, and penetrate the intestinal wall to form firm, encapsulated nodules > these rupture in 5-8 days> worms released in intestinal lumen and mature > copulate> eggs from the female are then deposited in the feces

TYPICAL CLINICAL FINDINGS:

• Weight loss and diarrhea
• Submandibular edema ("bottle jaw") in ruminants
• "Thin sow syndrome" - a chronic infection with periodic acute flare-ups
• Rarely causes peritonitis via perforation or rarely migrate to the skin and cause cutaneous nodules
• High mortality with heavy infections (calves, lambs)

TYPICAL GROSS FINDINGS:

• Granulomas within the mesentery, small intestine, or colon
• Elevated firm nodules on the serosal surface of the large intestine, cecum, and mesentery; may also be in ectopic sites such as kidney and diaphragm
  • Lesions with hemorrhage may be brown or black and older lesions may mineralize

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Granuloma or granuloma-like structure with eosinophils, central necrotic debris, and nematode within intestine wall or in serosa
• Parasites approximately 300 μm in diameter with a thick cuticle
• Platymyarian musculature
• Low lateral chords
• Pseudocoelom
• Triradiate esophagus
• Large intestine lined by a few multinucleated cells with a prominent brush border
• Reproductive tract

ADDITIONAL DIAGNOSTIC TESTS:

• Occasional fecal float will be positive – eggs look like other Strongylidae

DIFFERENTIAL DIAGNOSIS:

• Mesenteric lymphadenitis
• Mycobacterium bovis

COMPARATIVE PATHOLOGY:

• Reported in cattle, sheep, goats, wild pigs, and primates; humans are accidental hosts
• Sheep and goats in North America: Oesophagostomum columbianum
• Cattle all over the world: Oesophagostomum radiatum
• Pigs: Oesophagostomum dentatum

REFERENCES:

1. Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology;1999:8,24.
2. Strait K, Else JG, Eberhard ML. Parasitic disease of nonhuman primates. In: Abee CR, Mansfield K, Tardif S, Morris T, eds. Nonhuman Primates in Biomedical Research. Vol 2. Diseases. 2nd ed. San Diego, CA: Elsevier, Inc. 2012: 232-233.
3. 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 Ltd; 2016:115-116, 215.

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