Traveler's diarrhea pathophysiology

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Pathophysiology

• The transmission and pathogenesis of traveler's diarrhea is dependent on the infectious agent.
• The following table summarizes the natural reservoir, transmission, and pathogenesis of common infectious agents associated with traveler's diarrhea:

Infectious Agent	Characteristics	Reservoir	Common Mode of Transmission	Pathogenesis
E. coli (ETEC)	Gram-negative rod|| Humans and animals|| Fecal-oral route Contaminated ground beed, unpasteurized mild, cheese, vegetables, or water|| Enterotoxin-mediated: secretion of heat-labile toxin (LT) and heat-stable toxin (ST)
Campylobacter jejuni	Gram-negative rod|| Humans and animals|| Fecal-oral route*Contaminated meat, unpasteurized mild, cheese, vegetables, or water*Exposure to infected animals|| Enterotoxin-mediated: secretion of cholera-like enterotoxin
Shigella spp.	Gram-negative rod|| Humans only|| Fecal-oral route*Contaminated meat and pork, unpasteurized mild, cheese, vegetables, or water|| Low inoculum sufficient for infection (resistant to gastric acid)*Enterotoxin-mediated: secretion of Shiga toxin Invasion of macrophages and induction of cellular apoptosis Intracellular spread by actin polymerization processes (rocket propulsion)
Salmonella spp.	Gram-negative rod|| S. typhi: Humans only Other Salmonella spp.: Humans and animals|| Fecal-oral route Contaminated raw egg shells, poultry, unpasteurized mild, cheese, vegetables, or water|| High inoculum sufficient for infection (inactivated by gastric acid) Vi capsule endotoxin prevents opsonization and lysis Spread through the reticuloendothelial system
Norovirus	Positive-sense, single-stranded RNA virus|| Humans and animals|| Fecal-oral route Contaminated food, vegetables, and water Fomites Aerosol exposure|| Virus uses P2 subdomain for binding and HBGA for attachment on host cell
Rotavirus	Double-stranded RNA virus|| Humans and animals|| Fecal-oral route Fomites|| Poorly understood pathogenesis Viral replication in villous epithelium of host small intestine
Giardia lamblia	Anerobic, flagellated protozoan parasite|| Humans and animals|| Ingestion of cysts in water or uncooked foods Fecal-oral route|| Attaches to the epithelium by a ventral adhesive disc, and reproduces via binary fission Usually luminal infection, no hematogenous spread
Entamoeba histolytica	Anaerobic parasitic protozoan with pseudopods|| Humans*Rare (but present) in animals|| Ingestion of cysts in water*Fecal-oral route|| Excystation in the small intestine and migration to the large intestine Luminal and extraluminal infection, hematogenous spread common
Cryptosporidium	Spore-forming parasite||*Humans and animals|| Ingestion of oocytes in water*Fecal-oral route|| Minimally invasive, surface-level mucosal inflammation Usually luminal infection, potential to infect biliary tree