Shigella and Shigellosis
Shigella Overview
- Classification:
- Gram-negative rods
- Nonmotile and non-endospore-forming
- Do not produce urease or hydrogen sulfide
- Hosts:
- Primarily human parasites
- Can infect primates
- Disease Impact:
- All species cause similar diseases with varying intensity
- Closely resemble pathogenic E. coli
Signs and Symptoms of Shigellosis
- Symptoms include:
- Frequent, watery stools
- Fever
- Intense abdominal pain
- Nausea and vomiting
- Stools may contain:
- Obvious blood
- Occult blood (not visible to the naked eye)
- Mucus from the GI tract
- Dysentery:
- Diarrhea containing blood
Pathophysiology of Shigellosis
- Invasion:
- Shigella invades villus cells of the large intestine instead of the small intestine
- Less invasive compared to Salmonella (does not perforate the intestine or invade the bloodstream)
- Enters intestinal mucosa via special cells in Peyer's patches
- Inflammation and Damage:
- Initiates an inflammatory response causing extensive tissue destruction
- Releases endotoxins causing fever
- Produces enterotoxin damaging mucosa and villi, resulting in:
- Local erosion and bleeding
- Heavy mucus secretion
- Shiga Toxin:
- Produced by Shigella dysenteriae; a heat-labile exotoxin
- Responsible for severe intestinal damage and systemic effects (e.g., nerve cell injury)
Transmission and Epidemiology
- Transmission Routes:
- Usual oral route
- Direct person-to-person contact (small infectious dose: 10 to 200 bacteria)
- Associated Conditions:
- Poor sanitation, malnutrition, crowding
- Common in daycare centers, prisons, mental institutions, nursing homes, military camps
- Chronic Carrier:
- Some individuals may carry the bacteria for several months
- Recent Trends:
- CDC reported an increase in drug-resistant Shigella strains in 2023
Prevention and Treatment
- Prevention:
- Good hygiene practices
- Avoiding contact with infected individuals
- Treatment:
- No antibiotics in uncomplicated cases
- For immunocompromised patients, ciprofloxacin is recommended