Lawsonia intracellularis D-B15



September 2018




SIGNALMENT: (JPC 3064906): Female weaner pig


HISTORY: D-B15A This animal is from a group of weanlings pigs all with loose stools and fair body condition.


HISTOPATHOLOGIC DESCRIPTION: Large intestine: Multifocally there are elevated pedunculated plaques of mucosa, up to 3mm, composed of severely dilated and hyperplastic, tortuous crypts, with diffuse expansion of the lamina propria by a lymphoplasmocytic and eosinophilic infiltrate, increased clear space, and ectatic blood vessels and lacteals (congestion and edema). Diffusely, there is marked epithelial hyperplasia of the crypts characterized by elongated epithelial cells up to 7-8 cell layers thick that have crowded, often overlapping basophilic nuclei and frequent mitotic figures. There is an overall decrease in goblet cells. Multifocally, crypts are dilated, lined by attenuated epithelium, and contain numerous nondegenerate and degenerate neutrophils, sloughed epithelial cells and cellular and nuclear debris (crypt abscesses). Multifocally there are small amounts of fibrin and debris adherent to the superficial mucosa as well as focal areas of hyperplastic crypt epithelium directly adjacent to the muscularis mucosa.


MORPHOLOGIC DIAGNOSIS: Large intestine: Enteritis, proliferative and lymphoplasmacytic, chronic, multifocal, moderate, with crypt ectasia and goblet cell loss, breed unspecified, porcine.



SIGNALMENT: (JPC #2415686): A ferret




HISTOPATHOLOGIC DESCRIPTION: Colon: Multifocally, the mucosa is markedly hyperplastic and forms papillary, adenomatoid projections that extend up to 2mm into the lumen and are composed of deep, often tortuous crypts lined by hyperplastic epithelium with plump, elongated cells with cytoplasmic basophilia,vesiculate nuclei that pile up to 4-5 cells layers thick, and frequent mitotic figures within all layers of the villi. There is a marked paucity of goblet cells. Multifocally, crypts are dilated, lined by attenuated epithelium, and contain numerous nondegenerate and degenerate neutrophils, sloughed epithelial cells and cellular and nuclear debris (crypt abscesses). The lamina propria and submucosa are moderately expanded by lymphocytes, plasma cells, neutrophils and macrophages with few eosinophils.



D-B15C (Warthin Starry): Colon: There are many argyrophilic, curved 1x5um bacilli concentrated in the apical cytoplasm of hyperplastic mucosal and glandular 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.



SIGNALMENT: (JPC #1547835) An adult hamster


HISTORY: D-B15D Presented with diarrhea.


HISTOPATHOLOGIC DESCRIPTION: Ileum: In approximately 75% of the tissue section there is a loss of differential staining with retention of tissue architecture (coagulative necrosis) and/or complete loss of normal tissue architecture with replacement by necrotic debris (lytic necrosis) admixed with fibrin, hemorrhage and edema; necrosis extends transmurally thru the intestine wall from mucosa to serosa in some areas, and only affects the mucosa in other areas. In areas bordering the coagulative and lytic necrosis, individual enterocytes show cytoplasmic hypereosinophilia, with nuclear pyknosis and karyolysis(necrosis). In the remaining tissue, there are deep, often tortuous crypts and irregularly hyperplastic, blunted, and fused villi. Multifocally in the non-necrotic ileum there is marked mucosal hyperplasia with formation of papillary projections that extend up to 2mm into the intestinal lumen. Hyperplastic mucosal epithelium is characterized by cytoplasmic basophilia, vesiculate nuclei that pile up to 5-6 cell layers thick, frequent mitotic figures in all layers and decreased numbers of goblet cells. The lamina propria is 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 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



·       L. 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



·       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

·       Restricted to intestinal epithelium; organ dissemination has not been documented

·       Clinical disease does not develop in gnotobiotic pigs challenged with L. intracellularis



·       Pigs develop three main clinical presentations:

  • Proliferative hemorrhagic enteropathy (PHE): Young adults 4-12 months of age

o   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

o   Chronic form with diarrhea, anorexia and poor growth

o   Intestinal crypt hyperplasia

  • Necrotic enteritis

o   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:

·       Most consistent finding is hypoproteinemia

·       Postweaning foals 2-8 months of age or adults

·       Lethargy, anorexia, fever, peripheral edema, weight loss, colic, and diarrhea

·       Other species show similar signs as above



·       Proliferative and/or necrotizing enteritis

·       Thickening and corrugation (cerebriform) of mucosal and serosal surfaces of intestine,

·       In PHE – often with 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

·       Rats – ascending colon

·       Guinea pigs – jejunum and ileum



·       Marked enterocyte proliferation in the intestinal crypts with intracytoplasmic bacteria in the apical area

·       Elongated, enlarged, and crowded immature crypt epithelial cells

·       Termed “adenomatosis”

·       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 may result in progressive stricture of the lumen

·       External muscle layers of the intestine are often hypertrophied

·       Inflammatory infiltrate is variable



·       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



·       Silver methods (Warthin-Starry, Steiner)

·       PCR

·       IHC

·       Tissue culture (bacteria cannot be grown on cell-free media)



·       Enteritis in pigs:

  • Swine dysentery (Brachyspira hyodysenteriae): Large bowel only; argyrophilic spirochetes in mucus layer
  • Trichuris suis: Mucohemorrhagic typhlocolitis
  • Salmonella Typhimurium: Fibrinous and erosive, mainly of cecum and colon but can be in terminal ileum
  • Clostridium perfringens type C: 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): Diarrhea in adult hamsters; hepatic necrosis; no proliferative lesions

·       Salmonellosis (Typhimurium and Enteritidis): Diarrhea; also necrotizing splenitis and hepatitis

·       Clostridium difficile: Acute colitis and death associated with certain antibiotics

·       E. coli: Enteritis with blunting and fusion of villi

·       Helicobacter sp.: proliferative gastric mucosa with lymphoplasmacytic infiltrates; may progress to gastric carcinoma

·       Giardiasis



  • Mice – experimental infection; hyperplastic inflammation in ileum and colon
  • Rabbits – microscopic lesions range from suppurative and erosive to proliferative lesions; histiocytes with PAS-positive intracellular material often prominent in lamina propria
  • 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
  • Case report of a proliferative enteropathy in chickens, affecting primarily the villous epithelium as opposed to crypt epithelium



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. Guedes RM, Machuca MA, et. al. Lawsonia intracellularis in pigs: Progression of Lesions and Involvement of Apoptosis. Vet Pathol. 2017. 54(4):620-628.

3. Ohta T, Kimura K, et. al. Proliferative enteropathy caused by Lawsonia intracellularis in chickens. J Comp Pathol. 2017. 156:158-161.

4. 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.

5. Vannucci FA, Gebhart CJ. Recent advances in understanding the pathogenesis of Lawsonia intracellularis infections. Vet Pathol. 2014. 51(2):465-477.

6. 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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