Traveler's diarrhea pathophysiology

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Overview

The transmission and pathogenesis of traveler's diarrhea is dependent on the infectious agent. The majority of organisms associated with traveler's diarrhea are transmitted by the fecal-oral route and by contaminated food (meat, unpasteurized milk, cheese, vegetables, and fruits). The pathogenesis and mechanism of infection depends on the infectious agent. In E. coli traveler's diarrhea (most common), the organism secretes 2 endotoxins, heat-labile toxin (LT) and heat-stable toxin (ST), to induce clinical manifestations.

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
Bacteria
E. coli (ETEC)	Gram-negative rod	Humans and animals	Fecal-oral route Contaminated ground beef, unpasteurized milk, 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 milk, 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 milk, 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 milk, 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
Viruses
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
Protozoa
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 protozoa 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 spp.	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