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PATHOPHYSIOLOGY

There are numerous causes of Diarrhoea, but in almost all cases, this disorder is a manifestation of one of the four basic mechanisms described below. It is also common for more than one of the four mechanisms to be involved in the pathogenesis of a given case.


Osmotic Diarrhoea

Absorption of water in the intestine depends on adequate absorption of solutes. If excessive amount of solutes retained in the intestinal lumen, water will not be able to absorbed and Diarrhoea will be the result.
 

Secretory Diarrhoea

Large volumes of water are normally secreted into the small intestinal lumen, but a large majority of this water is efficienty absorbed before reaching the large intestine. Diarrhoea occurs when secretion of water into the intestinal lumen exceeds absorption.

Inflammatory and Infectious Diarrhoea
The epithelium of the digestive tube is protected from insult by a number of mechanisms constituting the gastrointestinal barrier, but like many barriers, it can be breached. Disruption of the epithelium of the intestine due to microbial or viral pathogens is a very common cause of Diarrhoea in all species. Destruction of the epithelium results not only in exudation of serum and blood into the lumen but often is associated with widespread destruction of absorptive epithelium. In such cases, absorption of water occurs very inefficiently and Diarrhoea results.

Diarrhoea Associated with Deranged Motility

In order for nutrients and water to be efficiently absorbed, the intestinal contents must be adequately exposed to the mucosal epithelium and retained long enough to allow absorption. Disorders in motility that accelerate transit time could decrease absorption, resulting in Diarrhoea even if the absorptive process was proceeding properly.

CLINICAL TYPES OF DIARRHOEA

It is the most practical to base treatment of Diarrhoea on the clinical type of the illness, which can easily be determined when a child is first examined. Laboratory studies are not needed. Several clinical types of Diarrhoea can be recognized, each reflecting the basic underlying pathology & altered physiology:


1. Acute Diarrhoea
 

· Acute watery Diarrhoea (including cholera) which lasts     several hours or days: The main danger is dehydration;    weight loss also occurs if feeding is not continued;
· Acute bloody Diarrhoea (also called dysentery): The    main    dangers are intestinal damage, sepsis and    malnutrition; other complications, including dehydration,    may also occur,    but less common then    secretory    Diarrhoea.

2. Persistant Diarrhoea

· Persistant Diarrhoea with acute onset (which lasts 14 days or    longer): The main danger is malnutrition and serious non-   intestinal infection; dehydration may also occur, even death is    high in malnourished children.

· Diarrhoea due to Immunocompromised host (HIV/AIDS    patients)


3. Diarrhoea due to other causes

· Diarrhoea with severe malnutrition (marasmus or kwashiorkor):  The main dangers are: severe systemic infection,      dehydration, heart failure and vitamin and mineral    deficiency.


4. Diarrhoea associated with malnutrition

CLINICAL FEATURES

 

Pathogen Common Epidemiological Settings or Modes of Transmission

Clinical Features
Fever Abdominal Pain Bloody Stool Vomiting, Nausea or Both Fecal Evidence of Inflammation Heme-positive Stool
Salmonella Outbreaks due to foodborne transmission, community-acquired Common Common Occurs Occurs Common Variables
Campylobacter Community-acquired, consumption of undercooked poultry Common Common Occurs Occurs Common Variables
Shigella Community-acquired, person-to-person Common Common Occurs Occurs Common Variables
Shigella toxin- producing E.Coli Outbreaks due to foodborne transmission, especially through ingestion of undercooked items Atypical Common Common Occurs Often not found Common
C.difficille Nosocomial spread, antibiotic use Occurs Occurs Occurs Not Common (NC) Common Occurs
Vibrio Ingestion of sea food Variable Variables Variables Variables Variables Variables
Yersinia Community-acqired, foodborne transmission Common Common Occurs Occurs Occurs Occurs
E.histolytica Travel to tropical regions, recent immigration from such countries Occurs Occurs Variables Variables Variables Common
Cryptosporidium Outbreaks due to water borne transmission, travel, immunocompromised hosts Variable Variables NC Occurs None to mild NC
Cyclosporal Outbreaks due to foodborne transmission, travel Variable Variables NC Occurs NC NC
Giardia Day care, outbreaks due to waterborne transmission, IgA deficiency NC Common NC Occurs NC NC
Rotavirus Summer outbreaks of vomiting or Diarrhoea in families, nursing homes, schools or on cruise ships or after ingestion of undercooked items Variable Common NC Common NC NC

Table - 2 : Epidemiological Settings and Clinical Features of
Infection with Selected Diarrhoeal Pathogens
1816-1826 : First Cholera pandemic:                        The pandemic began in                         Bengal, and then spread                         across India by 1820.

1829-1851 : Second Cholera                        pandemic reached                        Europe, London and                        Paris in 1832

1961-1970s : Seventh Cholera                          pandemic began in                          Indonesia, called El Tor                          after the strain, and                          reached Bangladesh in                          1963
 
1816-1826 : First Cholera pandemic:                        The pandemic began in                         Bengal, and then spread                         across India by 1820.

1829-1851 : Second Cholera                        pandemic reached                        Europe, London and                        Paris in 1832

1961-1970s : Seventh Cholera                          pandemic began in                          Indonesia, called El Tor                          after the strain, and                          reached Bangladesh in                          1963
 
1816-1826 : First Cholera pandemic:                        The pandemic began in                         Bengal, and then spread                         across India by 1820.

1829-1851 : Second Cholera                        pandemic reached                        Europe, London and                        Paris in 1832

1961-1970s : Seventh Cholera                          pandemic began in                          Indonesia, called El Tor                          after the strain, and                          reached Bangladesh in                          1963
 
1816-1826 : First Cholera pandemic:                        The pandemic began in                         Bengal, and then spread                         across India by 1820.

1829-1851 : Second Cholera                        pandemic reached                        Europe, London and                        Paris in 1832

1961-1970s : Seventh Cholera                          pandemic began in                          Indonesia, called El Tor                          after the strain, and                          reached Bangladesh in                          1963