Bacillary Dysentery (Shigella)

Overview

Plain-Language Overview

Bacillary Dysentery (Shigella) is an infection that affects the large intestine, causing inflammation and damage to the bowel lining. It is caused by bacteria called Shigella, which spread through contaminated food, water, or close contact with an infected person. The main symptoms include bloody diarrhea, abdominal pain, and fever. This condition can lead to dehydration due to frequent loose stools. It primarily affects the digestive system and can cause significant discomfort and illness, especially in young children and the elderly. Prompt diagnosis and treatment are important to manage symptoms and prevent complications.

Clinical Definition

Bacillary Dysentery (Shigella) is an acute infectious colitis caused by invasive Shigella species, primarily S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. The pathogenesis involves bacterial invasion of the colonic mucosa, leading to mucosal ulceration, intense inflammatory response, and bloody, mucoid diarrhea. The infection is transmitted via the fecal-oral route and is highly contagious. Clinically, it presents with fever, abdominal cramps, tenesmus, and dysentery characterized by frequent passage of small-volume stools containing blood and mucus. The disease is significant due to its potential for causing severe dehydration, systemic toxicity, and complications such as hemolytic uremic syndrome in certain strains. Diagnosis and management are critical to reduce morbidity and prevent outbreaks.

Inciting Event

Ingestion of contaminated food or water containing Shigella bacteria
Direct fecal-oral contact with an infected person
Outbreaks in crowded settings such as daycare centers or refugee camps

Latency Period

1 to 7 days from exposure to symptom onset, typically 1-3 days

Diagnostic Delay

Initial misattribution to viral gastroenteritis due to overlapping symptoms
Lack of stool culture or delayed stool testing for Shigella species
Mild or atypical presentations leading to under-recognition
Empiric treatment without microbiologic confirmation

Clinical Presentation

Signs & Symptoms

Frequent bloody diarrhea with mucus is the hallmark symptom of bacillary dysentery.
Abdominal cramps and pain are common due to colonic inflammation.
Fever and malaise often accompany the gastrointestinal symptoms.
Tenesmus or painful straining during defecation is characteristic.
Nausea and vomiting may occur but are less prominent.

History of Present Illness

Acute onset of high fever and abdominal cramps followed by diarrhea
Progression to bloody, mucoid stools with tenesmus and urgency
Associated symptoms include nausea, vomiting, and malaise
Symptoms typically last 5-7 days but can persist longer

Past Medical History

Previous episodes of gastrointestinal infections may increase suspicion
History of immunosuppression or malnutrition can worsen disease severity
Recent travel to endemic areas or contact with infected individuals

Family History

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Physical Exam Findings

Abdominal tenderness localized to the lower quadrants is common in bacillary dysentery.
Signs of dehydration such as dry mucous membranes and decreased skin turgor may be present.
Fever is often observed during the acute phase of infection.
Tenesmus with visible straining during rectal examination may be noted.
Blood and mucus in stool can sometimes be seen on digital rectal exam.

Diagnostic Workup

Diagnostic Criteria

Diagnosis of bacillary dysentery is established by identifying Shigella species in stool culture or by PCR-based assays detecting bacterial DNA. The presence of bloody, mucoid stools with numerous leukocytes on stool microscopy supports the diagnosis. Clinical features such as dysentery symptoms combined with positive stool cultures confirm the infection. Additional tests may include stool antigen detection or serotyping to identify specific Shigella strains.

Pathophysiology

Key Mechanisms

Invasion of colonic mucosa by Shigella species causing mucosal ulceration and inflammation
Production of Shiga toxin leading to epithelial cell damage and bloody diarrhea
Neutrophil recruitment causing intense inflammatory response and tissue destruction
Disruption of water and electrolyte absorption resulting in diarrhea and dehydration

Involvement	Details
Organs	Colon is the main organ affected, where Shigella invades epithelial cells causing inflammation, ulceration, and dysentery symptoms.
Tissues	Colonic mucosa is the primary site of Shigella invasion and ulceration, leading to characteristic bloody diarrhea.
Cells	Neutrophils are recruited to the colonic mucosa and mediate tissue damage and pus formation in bacillary dysentery.
	Macrophages phagocytose Shigella but the bacteria can escape the phagosome to invade epithelial cells.
	Colonic epithelial cells are invaded and destroyed by Shigella, leading to mucosal ulceration and bloody diarrhea.
Chemical Mediators	Interleukin-1 (IL-1) is released by infected macrophages, promoting inflammation and fever in bacillary dysentery.
	Tumor necrosis factor-alpha (TNF-α) amplifies the inflammatory response causing mucosal injury and systemic symptoms.
	Prostaglandins contribute to increased intestinal secretion and motility, worsening diarrhea.

Treatments

Pharmacological Treatments

Ciprofloxacin
- Mechanism:
  - Inhibits bacterial DNA gyrase and topoisomerase IV, preventing DNA replication in Shigella.
- Side effects:
  - Tendon rupture
  - Gastrointestinal upset
  - Photosensitivity
- Clinical role:
  - First-line
Azithromycin
- Mechanism:
  - Binds to the 50S ribosomal subunit, inhibiting bacterial protein synthesis in Shigella.
- Side effects:
  - Gastrointestinal upset
  - QT prolongation
  - Hepatotoxicity
- Clinical role:
  - First-line
Trimethoprim-sulfamethoxazole
- Mechanism:
  - Inhibits sequential steps in bacterial folate synthesis, impairing DNA synthesis in Shigella.
- Side effects:
  - Rash
  - Bone marrow suppression
  - Hyperkalemia
- Clinical role:
  - Second-line

Non-pharmacological Treatments

Maintain adequate hydration with oral rehydration solutions to prevent dehydration from diarrhea.
Implement strict hand hygiene and sanitation measures to reduce transmission of Shigella.
Avoid anti-motility agents as they may worsen the disease by prolonging bacterial toxin exposure.

Prevention

Pharmacological Prevention

No widely available vaccine currently exists for Shigella; antibiotic prophylaxis is not routinely recommended.
Antibiotic treatment of close contacts is sometimes used in outbreak settings to prevent spread.

Non-pharmacological Prevention

Hand hygiene with soap and water is critical to prevent fecal-oral transmission.
Safe drinking water and proper sanitation reduce infection risk.
Food safety measures including thorough cooking and avoiding contaminated food.
Isolation of infected individuals during outbreaks to limit spread.
Public health education on hygiene and sanitation practices.

Outcome & Complications

Complications

Hemolytic uremic syndrome (HUS) is a serious complication especially with Shigella dysenteriae type 1.
Severe dehydration from profuse diarrhea can lead to hypovolemic shock.
Sepsis may develop in immunocompromised or severely ill patients.
Rectal prolapse can occur in young children with severe dysentery.
Reactive arthritis may develop as a post-infectious complication.

Short-term Sequelae	Long-term Sequelae
Persistent diarrhea lasting beyond the acute phase may occur. Electrolyte imbalances such as hypokalemia due to fluid loss. Perianal irritation and ulceration from frequent stools. Secondary bacterial infections of the perianal skin.	Post-infectious irritable bowel syndrome (IBS) can develop after resolution. Chronic colitis with mucosal scarring is rare but possible. Growth retardation in children due to repeated or severe infections. Reactive arthritis may persist for months after infection.

Differential Diagnoses

Bacillary Dysentery (Shigella) versus Enterohemorrhagic Escherichia coli (EHEC) infection

Bacillary Dysentery (Shigella)	Enterohemorrhagic Escherichia coli (EHEC) infection
Infection with Shigella species invading colonic mucosa	Infection with Escherichia coli O157:H7 producing Shiga toxin
Bloody diarrhea with high fever and abdominal cramps	Often causes bloody diarrhea without high fever
Positive stool culture for Shigella species	Positive stool culture for E. coli O157:H7 or detection of Shiga toxin by PCR

Bacillary Dysentery (Shigella) versus Campylobacter jejuni infection

Bacillary Dysentery (Shigella)	Campylobacter jejuni infection
Infection with Shigella, a non-motile gram-negative rod	Infection with Campylobacter jejuni, a curved gram-negative rod
Often associated with fecal-oral transmission from contaminated water or food	Often associated with undercooked poultry or unpasteurized milk
Bloody diarrhea with prominent tenesmus and high fever	Diarrhea may be watery or bloody, often preceded by fever and malaise

Bacillary Dysentery (Shigella) versus Clostridioides difficile colitis

Bacillary Dysentery (Shigella)	Clostridioides difficile colitis
No recent antibiotic use; fecal-oral transmission common	Recent antibiotic use or hospitalization
Bloody diarrhea with mucus and severe abdominal cramps	Profuse watery diarrhea, often without blood
Positive stool culture or PCR for Shigella species	Positive stool toxin assay for C. difficile toxins A and B

Bacillary Dysentery (Shigella) versus Amebic dysentery (Entamoeba histolytica infection)

Bacillary Dysentery (Shigella)	Amebic dysentery (Entamoeba histolytica infection)
Infection with gram-negative bacterial Shigella species	Infection with protozoan parasite Entamoeba histolytica
Acute onset with mucosal ulceration and bloody diarrhea	Chronic or subacute course with flask-shaped ulcers and possible liver abscess
Positive stool culture or PCR for Shigella species	Detection of cysts or trophozoites in stool microscopy or antigen testing

Bacillary Dysentery (Shigella) versus Salmonella enterocolitis

Bacillary Dysentery (Shigella)	Salmonella enterocolitis
Infection with non-motile Shigella species	Infection with motile Salmonella species
Fecal-oral transmission from contaminated water or food	Often linked to contaminated poultry, eggs, or reptiles
Bloody diarrhea with high fever and tenesmus	Diarrhea often watery, may be bloody; fever usually moderate