Gastroenteritis

Introduction. 

Gastroenteritis is a general syndrome due to infections of the small and/or large intestine. Viral infections primarily affect the small intestine and include rotavirus, Calicivirus, Norwalk virus, Astrovirus, and adenovirus. Bacterial causes include Bacillus cereus, E. coli, Salmonella, Shigella, Yersinia, Clostridium, Vibrio, and Campylobacter. Several of these infections are unique enough to warrant their own name (e.g. cholera).

Bacterial gastroenteritis

1. Escherichia coli
   1. Enterotoxigenic E. coli
   2. Enteropathenogenic E. coli
   3. Enteroinvasive E. coli
   4. Enterohemorrhagic E. coli
   5. Enteroaggregative E. coli
   6. Diffusely aggregating E. coli
2. Salmonella spp.
3. Shigella spp.: Bacterial dysentery, Shiga toxins
4. Vibrio cholerae: Cholera toxin; causes epidemics; dehydration - rice-water stools
5. Vibrio parahaemolyticus: milder symptoms; 1 - 3 days watery diarrhea
6. Yersinia enterocolitica: diarrhea, fever, abdominal pain for 1 - 2 weeks
7. Campylobacter jejuni: most common cause of bacterial GE
8. Aeromonas hydrophila:
9. Bacillus cereus: ingestion of spores; heat-labile toxin

Summary of bacterial gastroenteritis

Cause: Campylobacter jejuni

• Microscopy: Comma-shaped Gram-negative
• Transmission: zoonotic; contaminated foods, milk, water
• Symptoms: Diarrhea (may be bloody), fever, malaise, abdominal pain; self-limited (1 week)
• Complications: Bacteremia (esp. C. fetus); Guillain-barre syndrome
• Pathogenesis: Adhesins for GI epithelium; invasion of epithelium via enterotoxins, cytotoxins, endotoxin
• Treatment: Supportive; erythromycin or tetracycline for severe cases or bacteremia

Cause: Vibrio parahaemolyticus 

• Microscopy: Gram-negative curved rod
• Transmission: Contaminated seawater, undercooked seafood (e.g. raw oysters)
• Symptoms: Explosive watery diarrhea; headache, cramps, nausea, vomiting, low fever
• Pathogenesis: Attachment to intestinal epithelium; hemolysin causes diarrhea via increased NaCl secretion
• Treatment: Self-limiting; antibiotics in severe cases

Cause: Yersinia enterocolitica

• Microscopy: Gram-negative rods
• Transmission: zoonotic; contamination of food/water
• Symptoms: Acute watery diarrhea, fever, abdominal pain (1-2 weeks)
• Complications: Chronic infection; transfusion-related bacteremia + shock
• Pathogenesis: Resist phagocytosis; cytotoxins
• Treatment: Self-limited infection

Cause: Shigella (4 species)

• Microscopy: Gram-negative rods
• Culture: Salmonella-Shigella agar
• Transmission: Fecal-oral person-to-person spread; 70% of cases are pediatric
• Symptoms: Abdominal cramps, diarrhea, fever, bloody stools
• Complications: Dysentery, HUS
• Pathogenesis: Enter M-cells, replicate in cytoplasm, induce apoptosis, damage intestinal lining = invasiveness. Shiga toxin inhibits protein synthesis and kills epithelial cells
• Treatment: Self-limited infection

Cause: Salmonella

• Microscopy: Gram-negative rods
• Transmission: contaminated food, water
  • zoonotic (S. typhimurium, S. cholerasuis)
  • Human reservoir (S. typhi, S. paratyphi) - Typhoid Mary
• Symptoms: fever, nausea, vomiting, diarrhea (may be bloody), cramps
• Complications: bacteremia
• Pathogenesis: Enter M-cells, replicate in phagosome, kill cells; cell-to-cell spread occurs; local inflammation also stimulates fluid secretion
• Treatment: self-limited

Cause: E. coli

• Microscopy: Gram-negative rods
• Transmission: Contaminated water or food (often zoonotic)
• Symptoms: mild diarrhea, nausea, vomiting, cramps, headache, bloody stools
• Complications: hemorrhagic colitis, HUS
• Pathogenesis: Enterotoxins, endotoxins, intracellular replication, fluid hypersecretion, microvilli damage, decreased absorption

Cause: Bacillus cereus

• Microscopy: Gram-positive endosporing rods
• Transmission: Contaminated food (meats, vegetables, sauces), rice (emetic form)
• Symptoms: diarrhea, nausea, cramps; vomiting (emetic form)
• Complications: rarely, fulminant liver failure (emetic toxin)
• Pathogenesis: Heat-labile enterotoxin stimulate adenylate cyclase; heat-stable enterotoxin

Viral Gastroenteritis: Summary

Cause: Rotavirus (Reovirus)

• Transmission: fecal-oral route
• Symptoms: watery diarrhea, fever, vomiting, nausea (onset ~ 48 hrs)
• Pathogenesis: Cytolytic damage to intestinal epithelium causes water and electrolyte loss. Diarrhea results, containing up to 10 billion virions per gram.
• Complications: Dehydration in infants and young children (> 500,000 deaths world-wide)
• Treatment: supportive
• Immunity: IgA lessening the severity of later infections
• Vaccine: Several available

Cause: Norovirus/Norwalk virus (Calicivirus)

• Transmission: fecal-oral (ID ~ 10)
• Symptoms: diarrhea, vomiting, cramping, nausea, abdominal pain; rapid onset (24 - 48 hrs)
• Pathogenesis: Infection of intestinal lining causes malabsorption of water and nutrients. Some cell damage occurs but resolves easily
• Complications: dehydration in infants
• Treatment: supportive
• Immunity: short-lived
• Vaccine: no
• Related viruses: Astrovirus, calicivirus

Cause: Adenovirus serotypes 40 - 42

• Transmission: fecal-oral
• Symptoms: diarrhea
• Pathogenesis: cytolytic infection of intestinal epithelium
• Complications: hospitalization (15% due to adenovirus)
• Treatment: supportive
• Vaccine: no

Links:

• http://www.wadsworth.org/databank/images/campylobacter.gif