JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
August 2021
D-B13

 

SIGNALMENT (JPC #1782684): 2-day-old piglet

 

HISTORY:  This animal had diarrhea.  There was 100% morbidity and 90% mortality in affected litters.

 

HISTOPATHOLOGIC DESCRIPTION:  Small intestine (multiple sections): Multifocally and frequently, there are aggregates of basophilic, 1x2 um bacilli carpeting approximately 80% of the mucosal epithelial apical brush border along villi and crypts.  Multifocally, intestinal villi are mildly blunted and enterocytes are occasionally sloughed/lost, swollen and vacuolated (degenerate), or shrunken with a scant amount of hypereosinophilic cytoplasm and a pyknotic nucleus (single cell death), and there are occasional neutrophils transmigrating the mucosal epithelium.  The lamina propria is multifocally infiltrated by low to moderate numbers of neutrophils, fewer lymphocytes, mild to moderate hemorrhage, fibrin, and edema.  Small caliber blood vessels are expanded up to two times normal (congestion).  Occasionally, multifocal crypt lumina contain necrotic cellular debris and few neutrophils (crypt abscesses).  The Peyer’s patches (GALT) within the submucosa of the ileum contain active germinal centers, up to 2mm diameter, which contain numerous tingible body macrophages (reactive lymphoid hyperplasia).  

 

MORPHOLOGIC DIAGNOSIS:  Small intestine, mucosa: Abundant apical surface-associated bacilli, multifocal to coalescing, with mild neutrophilic enteritis, few crypt abscesses, and mild GALT hyperplasia, porcine.

 

ETIOLOGIC DIAGNOSIS: Enteric colibacillosis

 

CAUSE:  Enterotoxigenic Escherichia coli

 

CONDITION: Enterotoxigenic colibacillosis

 

SYNONYMS:  ETEC, white scours, neonatal diarrhea, post-weaning diarrhea, young pig diarrhea, coliform gastroenteritis, baby pig diarrhea, coliform scours

 

GENERAL DISCUSSION:

• Gram-negative, facultative anaerobe, non-spore-forming bacillus; non-virulent strains are considered normal flora
• Major cause of neonatal diarrhea in calves, pigs, and lambs; and weanling pigs
• Risk factors include genetic susceptibility, failure of passive transfer, first gestation, poor nutritional plane, environmental contamination, low ambient temperature, or stress
• Diagnosis is based on clinical signs, minimal gross lesions, and basophilic bacilli lining the surface of relatively histologically normal small intestines
• 4 main types of antigens on which coli serotypes are based:
  • O antigen (somatic; lipopolysaccharide)
  • K antigen (capsular): may enhance ability of bacteria to colonize intestines
  • H antigen (flagellar)
  • F antigen (fimbral): important in enteric colonization; some adhesins are associated with certain serotypes and are relatively host specific

 

PATHOGENESIS:

• Enterotoxigenic coli (ETEC): Ingestion of virulent bacteria > adherence to small intestinal enterocytes (does not invade enterocyte) > colonization of mucus on enterocyte > toxin production causes non-structural alteration of cell membrane and fluid transport system > net secretion of fluid and electrolytes from the systemic circulation into the lumen of the gut > secretory diarrhea > dehydration > metabolic acidosis > shock > death
• Virulence factors:
  • Fimbriae / pili (colonization factor antigens): promote colonization of gut; coded by plasmids; antigenically distinct; over 20 types have been identified
    • Fimbriae commonly found in pigs: F4 (K88), F5 (K99), F6 (987P), F18, F41
    • Genetic resistance is related to age-related susceptibility (the presence or absence of the appropriate receptors in the small intestine; i.e. F18 causes post-weaning diarrhea, but not neonatal) and inherited resistance (i.e. some pigs lack epithelial cell receptors for F4)
  • Enterotoxin: Heat-labile toxin (LT; cAMP) or heat-stable toxin (STa, STb, EAST1; cGMP) open chloride channels that irreversibly move chloride, water, and sodium into the lumen (secretory diarrhea) causing death in less than 24 hours from dehydration and electrolyte imbalance if untreated
    • ETEC that causes neonatal diarrhea usually only product STa while in post-weaning diarrhea usually produces one or more enterotoxins

 

TYPICAL CLINICAL FINDINGS:

• Neonatal (0-4 days old) and post-weaning (2-4 weeks after) piglets with gray to yellow watery alkaline diarrhea; may lose up to 40% of total body weight due to dehydration, resulting in flaccid abdominal musculature, enophthalmos, and bluish-gray skin
• Morbidity is extremely variable (average 30-40%; up to 80%); mortality can reach 70% (neonatal) or 25% (post-weaning) in affected litters

 

TYPICAL GROSS FINDINGS: 

• Stomach and small intestine is flaccid, dilated, and fluid filled; stomach may contain curdled milk; venous infarcts on the greater curvature of the stomach

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Bacteria adherent to the mucosal epithelial cells of the jejunum and ileum; found on brush borders of villi and/or crypts of Lieberkühn
• Typically no damage to enterocytes
• Sometimes vascular congestion, mildly increased neutrophils/macrophages in the lamina propria, and villous atrophy

 

ULTRASTRUCTURAL FINDINGS:

• Bacterial fimbriae attached directly to the enterocyte or mucus coating

 

DIFFERENTIAL DIAGNOSIS:

• Enteropathogenic coli (EPEC): 1-4 days old and 2-3 weeks post-weaning; watery yellowish diarrhea, dehydration
• Rotavirus (type A, B, C): 1 day to 7 weeks (most common 2-3 weeks old); watery to pasty diarrhea (may be subclinical); enterocyte sloughing with replacement by cuboidal to squamoid cells and villus blunting/fusion.
• Clostridium perfringens type C: 1-14 days old; hemorrhagic or watery diarrhea and sudden death; segmental necrohemorrhagic enteritits in proximal 2/3 of small intestine.
• perfringens type A: 3-28 days; mild creamy diarrhea
• difficile: 5-21 days; creamy diarrhea and dehydration; necrotizing colitis and mesocolonic edema
• Cryptospirodium spp: 3 days to weaning; mild to moderate yellowish diarrhea
• Coccidiosis (Cystoisospora suis): 5-21 days; watery yellowish diarrhea; fibrinonecrotic pseudomembrane without blood; intracytoplasmic apicomplexan organisms
• Coronavirus (TGE, PED, PDCoV)
  • Transmissible gastroenteritits virus (TGE): All ages (most severe <3 weeks old); severe diarrhea, vomiting, high mortality (100%); severe diffuse atrophic jejunitits and ileitis
  • Porcine epidemic diarrhea virus (PED): All ages (severe in piglets <1 week); watery diarrhea, vomiting; diffuse atrophic jejunitits and ileitis
  • Porcine deltacoronavirus (PDCoV): All ages (worst in suckling pigs); watery diarrhea, vomiting; diffuse atrophic jejunitits/ileitis (less severe than TGE/PED)
• Strongyloides sp: 10 days+; diarrhea and ill-thrift; villous atrophy, granulomatous enteritis
  

COMPARATIVE PATHOLOGY:

Pathogenic E. coli Subtypes:

• ETEC (enterotoxigenic): secretional diarrhea in piglets, calves, lambs; lesser extent in dogs, horses
• EPEC (enteropathogenic): rabbits, pigs, dogs, cats
  • Attaches to enterocytes; does not invade them; associated with villus atrophy
  • Uncommon in domestic animals
• EHEC (enterohemorrhagic): rabbits, dogs, calves, pigs; ruminants are reservoirs
• EDEC: pigs 6-14 weeks (edema disease)
  • Type of ETEC (usually F18); endotoxin à systemic vascular endothelial injury
  • Edema in gastric mucosa, eyelids, spiral colon; encephalomalacia
• EIEC (enteroinvasive): lab animals, occasionally cattle/pigs
  • Internalized by enterocyte, disseminated through body
  • Poorly documented in domestic animals
  • A cause of septicemic colibacillosis
• ExPEC:
  • UPEC: dogs, cats, pigs
  • APEC: turkeys, chickens, commercial ducks
    • Local colibacillosis: omphalitis, cellulitis, salpingitis, orchitis, venereal colibacillosis, swollen head syndrome,
    • Colisepticemia: pericarditits, myocarditis, respiratory collapse, etc
    • Coligranulomas (Hjarre’s disease): liver, ceca, duodenum, mesentery

 

References:

1. Constable PD, Hinchcliff KW, Done SH, Grunberg W. Diseases of the Alimentary Tract: Nonruminant. In: Constable PD, Hinchcliff KW, Done SH, Grunberg W. Veterinary Medicine, A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses. 11th ed. St. Louis, MO: Elsevier; 2017:311-319.
2. Fairbrother JM, Nadeau E. In: Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine. 11th ed. Ames, IA: Wiley-Blackwell; 2019:807-823.
3. Nolan LK, Vaillancourt JP, Barbieri NL, Logue CM.   In: Swayne DE, ed. Diseases of Poultry. 14th ed.  Hoboken, NJ: John Wiley and Sons, Inc; 2020:770-808.
4. Gelberg HB. Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:333,376-377.
5. Koenig A. Gram-negative bacterial infections. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 4th ed. St Louis, MO: W.B. Saunders Company; 2012:351-352.                                                                                                                                                  
6. 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. Philadelphia, PA: Elsevier Saunders; 2016:112, 158-167.
7. Zachary JF. Mechanisms of microbial infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:158-159.

 

E. coli subtypes	Virulence Factors	Examples
Enteropathogenic (EPEC) / Attaching and Effacing (AEEC) ·         Osmotic diarrhea ·         Acute inflammatory response ·         Structural cellular alterations (attaching and effacing); does NOT invade enterocytes ·         Gross: granular and rough mucosa; hemorrhage and fibrin ·         Ultrastructure: pedestal formation beneath attachment	·         Locus for enterocyte effacement: pathogenicity island that controls attaching-effacing trait ·         Fimbriae: P and S ·         EPEC adherence factor ·         Esp A/B/D- bacterial proteins exported via type III secretion system into the host cell; Esp-b & -D create pore in host membrane to introduce Tir (translocated-intimin-receptor protein) ·         Tir “focuses” actinà forming “pedestal” ·         Intimin (bacterial outer membrane protein) binding to Tir (in host membrane) = Intimate Attachment	·         Generally uncommon in domestic animals ·         Diarrhea in rabbits, calves, pigs, lambs, dogs and humans ·         Most often seen in calves with other enteropathogens such as Cryptosporidium parvum, ETEC, coronavirus, BVD, coccidian
Enterohemorrhagic (EHEC, VTEC: verotoxin-producing, STEC: Shiga toxin-producing) ·         Acute inflammatory response ·         Structural cellular alterations; invades enterocytes ·         Targets colon ·         Gross: granular and rough mucosa; hemorrhage and fibrin ·         Ultrastructure: pedestal formation beneath attachment	·         Shiga toxin or Shiga-like toxins ·         Bind the host cell receptor globotriaosylceramide (Gb3)à inhibition of protein synthesis with subsequent necrosis ·         Primarily affects intestinal epithelium and vascular endothelium, due to the presence of Gb3 receptors in these tissues ·         Mucosal loss à lamina propria exposure à endotoxin (LPS) uptake	·         Lab animals, cattle, pigs, humans ·         Fibrinohemorrhagic enterocolitis in calves (under 4-weeks old) ·         Hemolytic uremic syndrome (humans) ·         Greyhound: cutaneous/renal glomerular vasculopathy – associated with 0157:H7
Enterotoxigenic (ETEC) ·         Secretory diarrhea ·         Non-inflammatory or mild neutrophilic inflammation ·         Non-structural cellular alterations;  does NOT invade enterocytes ·         No gross lesions	·         Fimbriae ·         Heat-labile toxins: LTIà similar to cholera toxin; LTIIà cAMP pathwayà irreversible secretion of electrolytes (Cl- esp)/H2O in gutà secretory diarrhea ·         Heat-stable toxins: STaà inhibition of Na/Cl co-transport and H2O absorption via ↑ in cGMP; STb (primarily associated with ETEC in pigs)à promotes secretion by stimulating prostaglandin E2 and 5-hydroxytrypamine	·         <4 days old or post weaning ·         Secretory diarrhea in neonatal pigs, calves, lambs, and humans ·         Common in pigs
Enteroinvasive (EIEC) ·         Enterocyte internalization à sepsis	·         Invade intestinal enterocytes and disseminate throughout body	·         Poorly documented in domestic animals ·         Only confirmed experimentally in neonatal swine ·         Results in septicemia with fibrinous arthritis, ophthalmitis, serositis, meningitis, white-spotted kidneys (cortical abscesses)
Edema disease, enterotoxemic colibacillosis (EDEC)	·         Adhesion involved in diffuse adherence (AIDA) with F18 ·         Enteric colonization with Shiga-toxin ( or verotoxin 2e; Stx2e) producing E. coli and classic enterotoxemia à targets vascular endothelium	·         Pigs: few weeks after weaning ·         Endothelial injury of arterioles and arteries -> edema; neurologic signs due to brain edema, edema also in eyelids, gastric sub mucosa, gallbladder, and mesentery of spiral colon
Septicemic colibacillosis ·         Generalized septicemia: enters via navel, upper respiratory tract, tonsil, intestine ·         Enteritis not always present	·         Colicin V (plasmid): encodes aerobactin: siderophore that helps survive in low iron environments, outer membrane protein to combat bactericidial components of serum, capsule to impede phagocytosis	·         Calves; less common in others species ·         Neonates most commonly affected ·         Multisystemic disease in poultry

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