Dysentery

Dysentery is a form of gastroenteritis characterised by the passage of diarrhoeal stools containing visible blood. Historically described as “the bloody flux”, it represents a significant global health problem, particularly in regions with inadequate sanitation and limited access to clean water. The illness can lead to substantial morbidity and mortality due to dehydration and systemic complications. Although many cases resolve without medical intervention, severe forms require prompt treatment to prevent life-threatening outcomes.

Overview and Causes

Dysentery arises primarily from infection of the large intestine, where inflammatory processes damage the mucosal lining. This condition is most commonly associated with two pathogens:

• Shigella bacteria, producing bacillary dysentery or shigellosis.
• Entamoeba histolytica, a protozoan responsible for amoebic dysentery (amoebiasis).

Other potential causes include chemical irritants, alternative bacterial species, protozoa and parasitic worms. Transmission generally occurs via the faecal–oral route, often through contaminated food or water in areas with poor sanitation. Person-to-person transmission may also occur in crowded conditions or where hygiene is inadequate.
The mechanism underlying dysentery involves intense inflammation, ulceration and tissue damage within the colon. Pathogens either invade intestinal tissue directly or release toxins that impair cellular function. This results in bloody stools, impaired nutrient absorption and fluid loss.

Signs and Symptoms

The presentation of dysentery varies depending on the causative organism, but several common features occur across cases:

• Frequent diarrhoeal stools containing blood, mucus or pus.
• Abdominal pain, cramping and rectal tenesmus (a persistent urge to defecate).
• Fever and general malaise.
• Dehydration indicated by dry mouth, reduced skin turgor and fatigue.

Symptoms generally appear within one to three days of exposure and often subside within a week. Severe forms may involve high fever, circulatory shock or delirium. In extreme cases, fluid loss can exceed one litre per hour. Temporary lactose intolerance may follow infection. Nausea and vomiting are uncommon but may be present.
Amoebic dysentery can occasionally progress beyond the intestines. If the protozoa enter the bloodstream, they may spread to the liver, lungs or brain, forming abscesses and causing more serious systemic disease.

Bacillary Dysentery

Bacillary dysentery is caused primarily by Shigella species. These bacteria are highly infectious, requiring only a small number of organisms to trigger disease. Infection may produce mild illness, but severe cases involve frequent bloody stools and pronounced abdominal discomfort.
Shigella infections are classified as invasive, as the bacteria penetrate and damage the mucosa. More than 160 million cases of shigellosis occur annually, predominantly in developing nations, and over a million deaths are attributed to this pathogen each year.
Other bacterial organisms can also produce bloody diarrhoea. Certain strains of Escherichia coli, including Shiga toxin-producing E. coli (notably E. coli O157:H7), cause similar illness. These strains produce toxins that disrupt intestinal cells, leading to haemorrhagic diarrhoea.

Amoebic Dysentery

Amoebic dysentery results from ingestion of cysts of Entamoeba histolytica. The parasite is widespread in tropical and subtropical regions, particularly where human faeces contaminate water sources or are used as fertiliser.
Once swallowed, the cysts travel unharmed through the acidic environment of the stomach, then release trophozoites in the intestines. These amoebae can burrow into the intestinal wall, causing ulcers and abscesses. Over time, they encyst again and are passed out of the body in faeces, continuing the transmission cycle.
Insufficiently treated amoebiasis may persist in the body for years, and dormant infection can later lead to severe complications, including liver abscesses and systemic involvement.

Pathogenesis and Mechanisms

Dysentery develops when pathogens colonise and damage the large intestine. Invasive species penetrate the mucosa directly, causing ulceration and bleeding. Toxigenic species secrete substances that damage or kill epithelial cells. The resulting inflammation leads to:

• Capillary leakage and swelling.
• Loss of water and electrolytes through diarrhoea.
• Release of immune mediators such as cytokines.
• Impaired nutrient absorption.
• Potential entry of pathogens into the bloodstream.

Chronic or severe blood loss can also produce anaemia.
Definitions may vary globally. Some clinicians limit dysentery to cases with visible blood, while others include severe diarrhoea with mucus or microscopic bleeding.

Diagnosis

Diagnosis usually begins with a medical history and physical examination. Dehydration is often evident through dry lips, reduced skin moisture or low blood pressure. Abdominal tenderness may also be detected.
Laboratory investigation plays a central role:

• Stool microscopy and culture identify the causative organism, though multiple samples may be required due to variability in pathogen shedding.
• Blood tests assess electrolyte imbalances or signs of systemic involvement.
• Distinction must be made between dysentery and other causes of blood in stools, such as haemorrhoidal bleeding or inflammatory bowel disease.

Prevention

Preventive measures focus on limiting faecal contamination:

• Proper handwashing.
• Ensuring safe food handling and drinking water.
• Avoiding uncooked foods in high-risk regions.
• Maintaining sanitation infrastructure, particularly in crowded or low-resource settings.

These strategies are essential when travelling to areas where dysentery is endemic.

Vaccination

There is currently no licensed vaccine against Shigella, although several candidates are under development. Vaccine research is particularly relevant for reducing childhood diarrhoeal disease in low-resource regions. Natural immunity appears to follow exposure, indicating feasibility for effective immunisation. Challenges include limited funding, technical constraints and insufficient commercial incentives. Most development efforts are conducted in the public sector or by biotechnology research organisations.

Treatment

Treatment aims to maintain hydration, manage symptoms and eliminate the underlying infection.

• Fluid replacement is vital. Oral rehydration solutions are commonly used to restore electrolytes and prevent dehydration.
• Antibiotics such as azithromycin may be indicated, especially for travellers’ diarrhoea or confirmed Shigella infection.
• Antidiarrhoeal medications like loperamide are generally not advisable alone, but may be combined cautiously with antibiotics in selected cases.
• Amoebic dysentery requires specific anti-protozoal therapy to prevent long-term complications or systemic spread.

Severe disease may necessitate hospital management for intravenous fluids or treatment of complications such as liver abscesses.

Global Burden and Epidemiology

Dysentery remains a major public health concern in many parts of the world. In regions lacking clean water and sanitation, nearly half of diarrhoeal disease cases are caused by Entamoeba histolytica. Millions of individuals are affected annually, and tens of thousands die from amoebiasis-related complications. Shigellosis is similarly widespread, producing substantial mortality in children and vulnerable populations.
Dysentery continues to represent a significant challenge for global health, particularly in lower-income countries. Although preventable through improved hygiene and sanitation, the disease persists where access to basic infrastructure is limited. Ongoing efforts in vaccine development, public health initiatives and education aim to reduce the impact of this long-recognised illness.