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Dysentery: Causes, Transmission, Diagnosis & Treatment

Dysentery is an intestinal infection characterized by frequent small-volume stools with blood and mucus, accompanied by abdominal cramps, tenesmus (urgency with incomplete evacuation), and fever. It signifies invasive colonic inflammation.

Major Etiologies

PathogenTypeKey FeaturesTransmission
Shigella spp. (S. flexneri, sonnei, dysenteriae, boydii)BacteriumMost common bacterial cause globally. Low inoculum (10-100 org). Invasive → colonic ulceration. S. dysenteriae type 1 → Shiga toxin → HUS.Fecal-oral: person-to-person, contaminated food/water, fomites. High secondary attack rate.
Entamoeba histolyticaProtozoanAmoebic dysentery. Trophozoites invade mucosa → flask-shaped ulcers. Can cause liver abscess. Cysts survive weeks in environment.Fecal-oral: cysts in contaminated water/food. Asymptomatic carriers shed cysts.
EIEC (Enteroinvasive E. coli)BacteriumBiochemically similar to Shigella. Same invasive mechanism. Less common.Food/water; person-to-person.
Salmonella (non-typhoidal)BacteriumUsually gastroenteritis; can cause dysentery (blood/mucus). Typhoidal (Typhi/Paratyphi) = systemic.Food (poultry, eggs, produce); animal contact.
Campylobacter jejuniBacteriumCommon foodborne. Dysentery-like illness. Precedes GBS (1:1000).Poultry, unpasteurized milk, water.
C. difficileBacteriumAntibiotic-associated. Toxins A/B → pseudomembranous colitis. Can present as dysentery.Spores in healthcare environment; community acquisition rising.

Diagnosis

  • Clinical: Blood/mucus + tenesmus + fever = dysentery.
  • Stool Studies:
    • WBCs / Lactoferrin / Calprotectin (inflammatory marker).
    • Culture (Shigella, Salmonella, Campylobacter, EIEC).
    • PCR Panel (GI pathogen panel — rapid, comprehensive).
    • O&P / Antigen / PCR for E. histolytica (distinguish from E. dispar).
    • C. diff NAAT/toxin.
  • Blood: CBC (leukocytosis, left shift), BMP, CRP.
  • Endoscopy: If unclear, severe, or biopsy needed (CMV, IBD, ischemic).

Treatment

Shigellosis

  • Antibiotics shorten duration, reduce shedding: Ciprofloxacin 500mg BID ×3d, Azithromycin 500mg daily ×3d, Ceftriaxone 2g IV daily (severe). Resistance common — test susceptibility.
  • No antimotility agents (loperamide) — may worsen.

Amoebiasis

  • Metronidazole 750mg TID ×7-10d (tissue trophozoites) → followed by Paromomycin 500mg TID ×7d (luminal cysts) or Iodoquinol.
  • Liver abscess: Metronidazole + aspiration if >5cm/impending rupture.

Other Bacterial

  • Campylobacter: Azithromycin 500mg daily ×3d (if severe/high risk).
  • Salmonella (non-typhoidal): Usually supportive; abx if severe/immunocompromised/extra-intestinal (Cipro/Azithro/Ceftriaxone).
  • C. diff: Fidaxomicin 200mg BID ×10d (1st line), Vancomycin 125mg QID ×10d.

Supportive

  • ORS (critical — dysentery loses significant fluid/electrolytes).
  • Zinc 20mg/day ×10-14d (children) — reduces duration/severity.
  • Avoid antimotility agents in febrile/bloody diarrhea.

Prevention

  • WASH: Safe water, sanitation, handwashing with soap.
  • Food Safety: Cook thoroughly, separate raw/cooked, peel fruit.
  • Vaccines: None licensed for Shigella/E. histolytica (in development). Typhoid vaccine for travelers.
  • Outbreak Control: Isolation, contact tracing, prophylaxis for household contacts (Shigella).

Complications

  • Dehydration/electrolyte imbalance (most common).
  • HUS (Shiga toxin: Shigella dysenteriae 1, STEC).
  • Toxic megacolon (C. diff, Shigella).
  • Intestinal perforation.
  • Reactive arthritis (Shigella, Salmonella, Campylobacter, Yersinia).
  • Post-infectious IBS.

Dysentery is a reportable disease in most jurisdictions. Prompt diagnosis, appropriate antimicrobials, and rehydration prevent mortality and spread.

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