JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
August 2021
D-B15

SLIDE A:

SIGNALMENT: (JPC #3064906): Female weaner pig

 

HISTORY: This animal is from a group of weanling pigs all with loose stools and fair body condition.

 

HISTOPATHOLOGIC DESCRIPTION: Colon: There are multifocal elevated pedunculated plaques of mucosa, measuring up to 3 mm wide, composed of severely dilated and hyperplastic, tortuous crypts. Within affected areas, there is marked epithelial hyperplasia of the crypts characterized by elongated epithelial cells piling up to 7-8 cell layers thick that have crowded, often overlapping nuclei and frequent mitotic figures; there is an overall decrease in goblet cells; and there are multifocal dilated crypts, lined by attenuated epithelium, containing numerous intact and necrotic neutrophils, sloughed epithelial cells, and cellular and nuclear debris (crypt abscess). There is diffuse expansion of the lamina propria by lymphocytes, plasma cells, eosinophils, increased clear space (edema), ectatic blood vessels (congestion), and rare dilated lacteals. Multifocally there are small amounts of fibrin and debris adherent to the superficial mucosa.

 

MORPHOLOGIC DIAGNOSIS: Colon: Colitis, proliferative and lymphoplasmacytic, chronic, multifocal, moderate, with crypt ectasia, crypt abscesses, and goblet cell loss, breed unspecified, porcine.

 

SLIDE B:

SIGNALMENT: (JPC #2415686): A ferret

 

HISTORY: None

 

HISTOPATHOLOGIC DESCRIPTION: Colon: There are multifocal papillary projections of hyperplastic, adenomatous mucosa comprising 30% of this section that extend up to 2 mm into the lumen and are composed of deep, often tortuous crypts lined by hyperplastic, plump, elongated epithelium with basophilic cytoplasm and vesicular nuclei that pile up to 4-5 cells layers thick, with frequent mitotic figures at all levels of the crypts (crypt hyperplasia). In affected areas, there is a marked decrease in goblet cells and multifocally crypts are dilated, lined by attenuated epithelium, and contain numerous intact and necrotic neutrophils, sloughed epithelial cells, and cellular and nuclear debris (crypt abscess). Diffusely, the lamina propria and submucosa are mildly expanded by lymphocytes, plasma cells, neutrophils, macrophages, and few eosinophils.

 

SLIDE C: (Warthin Starry): Colon: There are many argyrophilic, curved, 1 x 4 um bacilli concentrated in the apical cytoplasm of hyperplastic mucosal epithelial cells.

 

MORPHOLOGIC DIAGNOSIS: Colon: Colitis, proliferative, chronic, multifocal, moderate, with goblet cell loss, crypt abscesses, and numerous argyrophilic intraenterocytic bacilli, consistent with Lawsonia intracellularis infection, ferret (Mustela putorius furo), mustelid.

 

SLIDE D:

SIGNALMENT: (JPC #1547835): An adult hamster

 

HISTORY: Presented with diarrhea.

 

HISTOPATHOLOGIC DESCRIPTION: Ileum: Approximately 75% of the section exhibits either loss of differential staining with retention of tissue architecture (coagulative necrosis) or complete loss of normal tissue architecture with replacement by necrotic debris (lytic necrosis) admixed with fibrin, hemorrhage, and edema.  The necrosis multifocally extends transmurally through the intestinal wall from mucosa to serosa, and only affects the mucosa in other areas. In areas bordering the coagulative and lytic necrosis, individual enterocytes exhibit cytoplasmic hypereosinophilia with nuclear pyknosis and karyolysis (single cell death). In the non-necrotic tissue, there are deep, often tortuous crypts; irregularly blunted, and fused villi; and marked mucosal hyperplasia with formation of papillary projections that extend up to 2 mm into the intestinal lumen. Hyperplastic mucosal epithelium is characterized by cytoplasmic basophilia, vesiculate nuclei, epithelium piling up to 5-6 cell layers thick, frequent mitotic figures in all layers, and decreased numbers of goblet cells. The lamina propria is diffusely mildly expanded by a lymphoplasmocytic infiltrate with rare histiocytes. Multifocally the crypt epithelium herniates through the lamina propria into the submucosa and abuts the external muscular tunics.

 

MORPHOLOGIC DIAGNOSIS: Ileum: Ileitis, proliferative and necrotizing, chronic, diffuse, severe, with crypt abscesses and crypt herniation, hamster (Mesocricetus auratus), rodent.

 

ETIOLOGIC DIAGNOSIS: Lawsonial enterocolitis

 

CAUSE: Lawsonia intracellularis

 

CONDITION: Proliferative enteritis, porcine proliferative enteropathy (pigs), proliferative bowel disease (ferret), proliferative ileitis (hamster)

 

SYNONYMS: Porcine intestinal adenomatosis, proliferative ileitis, regional ileitis, garden hose disease (pig), acute proliferative hemorrhagic enteropathy, necrotic enteritis

 

GENERAL DISCUSSION:

• intracellularis is an obligate intracellular, curved, Gram-negative bacterium
• Previously known as “intestinal adenomatosis complex”, then believed to be a Campylobacter organism
• Colonizes enterocytes in the jejunum, ileum (always found in terminal portion for pigs), cecum, and colon, inducing crypt epithelial cell proliferation
• Emerging disease in horses; prevalent and important disease in swine; common in hamsters and ferrets; reported in many other species (rabbits, guinea pigs, chickens, etc.)
• Host specificity appears to exist to some extent (e.g. hamsters challenged with an equine isolate do not develop disease)
• 3 forms of disease in pigs:
  • 1) porcine proliferative enteropathy
  • 2) necrotic enteritis
  • 3) proliferative hemorrhagic enteropathy

• Remaining species primarily demonstrate proliferative lesions 

PATHOGENESIS:

• Hypothesized to be fecal-oral transmission leading to the invasion of enterocytes and replication in the apical cytoplasm of enterocytes
• Induces enterocyte proliferation by unknown mechanism
• Cell division is required for bacterial replication -> bacteria are passed onto daughter cells by extrusion from cytoplasm on villi or between crypt openings
• Infection is restricted to intestinal epithelium; organ dissemination has not been documented
• Clinical disease does not develop in gnotobiotic pigs challenged with intracellularis

 

TYPICAL CLINICAL FINDINGS:

• Pigs develop three main clinical presentations:
  • Proliferative hemorrhagic enteropathy (PHE): Young adults 4-12 months of age
    • Acute to subacute syndrome; exsanguination and death; massive intestinal hemorrhage; overt areas of hemorrhage or ulceration rarely seen grossly, but pronounced mucosal diapedesis is seen
  • Porcine proliferative enteropathy (PPE): Postweaned, 6-20 weeks of age
    • Chronic form with diarrhea, anorexia, and poor growth
    • Intestinal crypt hyperplasia
  • Necrotic enteritis
    • Possibly a separate syndrome or along a spectrum with PPE; coagulative necrosis with diphtheritic membrane formation; may be partly due to pathogenic anaerobic flora

• Ferrets: Young animals
  • Diarrhea, weight loss, dehydration, rectal prolapse, green-tinged feces, ataxia
• Hamsters: Young animals postweaning
  • Lethargy, anorexia, weight loss, watery diarrhea
  • Rectal prolapse or intussusceptions occur frequently
• Horses: Postweaning foals 2-8 months of age or adults
  • Most consistent finding is hypoproteinemia
  • Lethargy, anorexia, fever, peripheral edema, weight loss, colic, and diarrhea
• Other species show similar signs as above

 

TYPICAL GROSS FINDINGS:

• Proliferative and/or necrotizing enteritis
• Thickening and corrugation (cerebriform) of mucosal and serosal surfaces of intestine,
• Pigs with PHE: often have blood or fibrin clots in the intestinal lumen
• Most prominent in ileum, but also occurs in mid-jejunum, cecum, and proximal colon
• Variations between species as to which areas are most affected
  • Swine – Distal ileum always affected; other areas in addition
  • Horses – ileal-cecal junction
  • Rabbits – jejunum
  • Hamsters – ileum
  • New and Old World monkeys – distal ileum
  • Rats – ascending colon
  • Ferrets – Colon
  • Guinea pigs – jejunum and ileum
  • Ratite birds – distal ileum; distal rectum

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Marked enterocyte proliferation (“adenomatosis”) in the intestinal crypts with intracytoplasmic bacteria in the apical area
  • Elongated, enlarged, and crowded immature crypt epithelial cells
• Crypt abscesses with invasion of underlying structures
• Reduced number of goblet cells
• Coagulative necrosis
• Bouts of proliferation and necrosis in the distal ileum is followed by granulation tissue which may result in progressive stricture of the lumen
• External muscle layers of the intestine are often hypertrophied
• Inflammatory infiltrate is variable

 

ULTRASTRUCTURAL FINDINGS:

• Microvilli of affected cells are not well developed
• Bacteria located in the apical membrane of infected enterocytes and commonly associated with free ribosomes and scattered mitochondria
• Trilaminar outer bacterial envelope with electron-lucent zone between envelope and cytoplasmic membrane; single unipolar flagellum

 

ADDITIONAL DIAGNOSTIC TESTS (Campillo, JVDI, 2021):

• Silver methods (Warthin-Starry, Steiner)
• PCR
• IHC
• In situ hybridization (ISH)
• Tissue culture (bacteria cannot be grown on cell-free media)
• ELISA
• Indirect fluorescent antibody test (IFAT)

 

DIFFERENTIAL DIAGNOSIS:

• Enteritis in pigs:
  • Swine dysentery (Brachyspira hyodysenteriae, D-B16): Large bowel only; argyrophilic spirochetes in mucus layer
  • Trichuris suis: Mucohemorrhagic typhlocolitis
  • Salmonella Typhimurium (D-B01): Fibrinous and erosive, mainly of cecum and colon but can be in terminal ileum
  • Clostridium perfringens type C (D-B02): Hemorrhagic enteritis in piglets (jejunum and ileum)

• Ferrets with hemorrhagic or green tinged diarrhea:
  • Epizootic catarrhal enteritis (Coronavirus): Catarrhal mucoid green diarrhea (affects the small intestine)
• Hamsters:
• Clostridium piliforme (Tyzzer’s disease, D-B06): Diarrhea in adult hamsters; hepatic necrosis; no proliferative lesions
  • Salmonellosis (Typhimurium and Enteritidis, D-B01): Diarrhea; also necrotizing splenitis and hepatitis
  • Clostridium difficile: Acute colitis and death associated with certain antibiotics
  • coli: Enteritis with blunting and fusion of villi
  • Helicobacter (D-B18): proliferative gastric mucosa with lymphoplasmacytic infiltrates; may progress to gastric carcinoma
  • Giardiasis

 

COMPARATIVE PATHOLOGY:

• Mice – experimental infection; hyperplastic inflammation in ileum and colon
• Rabbits – microscopic lesions range from suppurative and erosive to proliferative; histiocytes with PAS-positive intracellular material often prominent in lamina propria
• Chickens – Report of a proliferative enteropathy in 2 chickens, affecting primarily the villous epithelium as opposed to crypt epithelium (Ohta, J Comp Pathol. 2017)
• Proliferative enteropathies caused by Lawsonia intracellularis have been described in non-human primates, blue and red fox, emu, ostrich, white-tailed and red deer, puppies (<3 months), wolves, rats, and guinea pigs

 

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, Iowa: John Wiley & Sons, Inc.; 2016:58,139-140,183-185,226,279-280.
2. Campillo M, Smith SH, Gally DL, Opriessnig T. Review of methods for the detection of Lawsonia intracellularis infection in pigs. J Vet Diagn Invest. 2021;33(4):621-631.
3. Delaney MA, Treuting PM, Rothenbuger JL. Lagomorpha. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA:Elsevier. 2018:491,494.
4. Delaney MA, Treuting PM, Rothenbuger JL. Rodentia. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA:Elsevier. 2018:509-510.
5. Guedes RM, Machuca MA, et. al. Lawsonia intracellularis in pigs: Progression of Lesions and Involvement of Apoptosis. Vet Pathol. 54(4):620-628.
6. Matz-Rensing K, Lowenstine LJ. New World and Old World monkeys. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA:Elsevier. 2018:360.
7. Ohta T, Kimura K, et. al. Proliferative enteropathy caused by Lawsonia intracellularis in chickens. J Comp Pathol. 2017. 156:158-161.
8. Smith DA. Palaeognathae: Apterygiformes, casuariiformes, rheiformes, struthioniformes; tinamiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA:Elsevier. 2018:644.
9. 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; 2016:177-180.
10. Vannucci FA, Gebhart CJ. Recent advances in understanding the pathogenesis of Lawsonia intracellularis Vet Pathol. 2014. 51(2):465-477.
11. Williams BH, Huntington KAB, Miller M. Mustelids. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA:Elsevier. 2018:298.
12. Zachary JF. Mechanisms of Microbial Infections. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:164-165.

 

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