What causes dysentery?

I don't think this disease needs any introduction; it's one of the most common diseases around the world, and I am sure most of us must have suffered from or encountered such cases.

But we always misinterpret the terms dysentery and diarrhea. These two are very similar, yet different. 

Diarrhea is a health condition where a person suffers from watery or loose stool. Dysentery is an infection or inflammation of the gut, most commonly the colon, which can lead to bloody or loose stool with blood/mucus.

What causes this dysentery. 

Dysentery is mainly caused by bacteria or protozoa (Entamoeba histolytica). And it is spread through feces in an oral way, which means mainly contaminated food. That's why it's very important to heat the food or wash your hands before eating.

Bacterial Dysentery:

So from bacteria, we got bacillary dysentery or bacterial dysentery. Some of the most common bacteria that cause this are

• Shigella, which can cause  to shigellosis.
• Salmonella, which can lead to salmonellosis.
• Campylobacter, which leads to campylobacteriosis.
• Escherichia coli causes an E. coli infection.

All this bacteria accumulates on intestine and cause most of the symptoms.

Lets discuss it more briefly: 

Shigellosis:

As the name suggests, this disease is due to a bacteria called Shigella. It typically spreads through contaminated food or water and can cause diarrhea, fever, and stomach cramps. It's important to practice good hygiene and food safety to prevent its spread.

When the bacteria are ingested, they primarily affect the intestine, more precisely the epithelial layer of the intestine. This bacteria also produces various toxins, including Shiga toxin and enterotoxins, which contribute to the symptoms of the infection. Shiga toxin, in particular, inhibits protein synthesis in host cells, leading to cell death and tissue damage. Enterotoxins stimulate fluid secretion in the intestines, resulting in watery diarrhea.

The invasion of epithelial cells and the release of toxins trigger a robust inflammatory response in the intestinal tissue. Immune cells, such as neutrophils and macrophages, are recruited to the site of infection, leading to tissue inflammation and damage. This inflammatory response further exacerbates the symptoms of Shigellosis, including fever, abdominal pain, and diarrhea.

Mechanism of action of Shigella bacteria 

Salmonellosis:

Salmonellosis also typically occurs when a person ingests food or water contaminated with Salmonella bacteria. Once ingested, the bacteria pass through the stomach and into the small intestine, where they adhere to the intestinal lining and invade the epithelial cells. Salmonella bacteria can also penetrate the intestinal mucosa and multiply within the intestinal cells, leading to inflammation and damage to the intestinal lining.

The infection triggers an immune response, attracting immune cells to the site of infection. In some cases, Salmonella can breach the intestinal barrier and enter the bloodstream, leading to systemic infection (typhoid fever in the case of Salmonella Typhi).

Salmonella bacteria produce various virulence factors, including toxins and proteins, which contribute to their ability to colonize and cause disease in the host. These factors enable Salmonella to evade host immune defenses, survive within host cells, and cause tissue damage.

Salmonellosis symptoms include  diarrhea (often bloody), abdominal cramps, fever, nausea, vomiting, headache, and muscle pain. Symptoms typically appear within 6 to 72 hours after exposure and can last for several days to a week.

Mechanism of action of Salmonella bacteria

Campylobacteriosis:

Campylobacteriosis typically occurs when a person consumes food or water contaminated with Campylobacter bacteria. Common sources of contamination include raw or undercooked poultry, unpasteurized milk, and untreated water.

Upon ingestion, Campylobacter bacteria reach the small intestine where they adhere to the epithelial cells lining the intestinal mucosa.This also produce toxin called cytolethal distending toxin (CDT),which can disrupts the normal funtion of intestinal cells.

The combination of bacterial attachment, toxin production, and inflammatory response disrupts the normal absorption of water and nutrients and leads to symptoms such as diarrhea, which is often watery or bloody, abdominal cramps, fever, and sometimes nausea and vomiting.

Transmission of Campylobacter 

E. coli infection:

E. coli bacteria are usually found in the intestines of humans and animals. While most strains are harmless, certain pathogenic strains, such as enterohemorrhagic E. coli (EHEC), can cause illness. These pathogenic strains can be transmitted through the consumption of contaminated food or water, contact with infected animals or their feces, or person-to-person contact. 

Strains of E. coli can cause Diarrhea 

Escherichia coli (E. coli) strains that cause dysentery typically produce toxins such as Shiga toxin or Shiga-like toxins. These toxins damage the lining of the intestines, leading to inflammation, ulceration, and bleeding. This results in the characteristic symptoms of dysentery, including severe abdominal pain, bloody diarrhea, and fever. E. coli dysentery is usually transmitted through contaminated food or water, and the bacteria colonize the intestines, where they release toxins and induce the inflammatory response.

So, Lets wrap up the Bacterial Dysentery.

Parasitic/ Protozoan Dysentery:

Amoebiasis:

Entamoeba histolytica is the protozoan parasite that causes amoebiasis, an intestinal infection in humans. 

When ingested, usually through contaminated food or water, the parasite can colonize the intestines, leading to symptoms such as diarrhea, abdominal pain, and fever. In severe cases, it can cause dysentery or bloody diarrhea. If the parasite spreads beyond the intestines, it can cause extraintestinal infections, such as liver abscesses. 

Life cycle of Entamoeba Histolytica 

It mainly causes ulcers in the intestine, where typically trophozoites of the protozoa reside. As a result of an ulcer, bloody diarrhea occurs. If we see the damaged region under a microscope, it looks like a flask, so it's called a flask-shaped ulcer. It primarily damages the mucosa and submucosa layers of the intestine, but it can't damage the muscularis layer as it is thicker. Which results in flask-shaped ulcers. 

Flask shaped ulcer formation in Amoebiasis 

So,these are some most common reasons for Dysentery.

It is a significant public health concern, particularly in areas with poor sanitation and hygien.Prevention strategies focus on improving sanitation, practicing good hygiene, and avoiding consumption of contaminated food and water.

In developing countries and regions with limited resources, dysentery remains a significant public health concern, particularly among children under five years old. In more developed regions with better sanitation infrastructure and access to healthcare, the incidence of dysentery may be lower but still occurs, especially in outbreaks or in populations with compromised immune systems.

Overall, while dysentery is preventable and treatable, it continues to affect millions of people globally each year, highlighting the importance of public health interventions aimed at improving sanitation, hygiene practices, and access to clean water sources.

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You can also watch this blog explanation on youtube

 What causes Dysentery?

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