Microbes Liable for Diarrhea and Dysentery and How Grow and Effect

Microbes Liable for Diarrhea and Dysentery and How Grow and Effect

Diarrhea is usually defined as the passage of three or more loose or watery stool in a 24-hour period, or stool frequency or liquidity that is considered abnormal by the mother. Exclusive breast-fed infants, normally pass several soft, semi-liquid stools each day. A loose stool being one that would take the shape of a container. In infants, stools volume in excess of 15 gm/kg/24 hour and from 3 years, stool output greater than 200grn/24 hour is considered diarrhea.

If the period of normal (formed) stools does not exceed two days, the illness should be considered a single diarrhea episode. If the period of normal stools is longer than two days, any subsequent diarrhea should be considered to be a new episode.
The diarrhea may be classified as acute watery diarrhea, dysentery and persistent diarrhea.

Acute Watery Diarrhea:

Diarrhea that begins acutely lasts less than 14 days without visible blood. Vomiting and lever may be present. The common etiologicalagents are enterotoxigenic Escherichia coli (ETEC), and Vibrio cholera 01. The others are rotavirus, salmonella, shigella, compylobacter jejuni.


This is diarrhea with visible blood in stool. The most important cause is Shigella, especially S.flexneri and S.dysenteriae type I. Others are Campylobacter jejuni, enteroinvasive E. coli, Salmonella, and Entamoeba histolylica.

Persistent diarrhea:

This is diarrhea that begins acutely but lasts for 14 days or more.


The infectious agents are usually spread by the fecal-oral route through contaminated food or water or direct contact. Vibrio cholera 01 and Shigella dysenteriae type 1, cause major epidemics. In temperate climates, bacterial diarrheas occur more frequently during the warm season, viral diarrheas, particularly disease caused by rota virus, peak during the winter. In tropical areas, rota virus diarrhea occurs throughout the year, increasing in frequency during the drier, cool months, whereas bacterial diarrhea peak during the warmer, rainy season. The following are the risk factors-

  1. Age under 2 years
  2. Failing to breast feed exclusively for the first 4-6 months of age,
  3. Artificial feeding with feeding bottles,
  4. Eating of stored cooked food for several hours at room temperature,
  5. Drinking water that is contaminated with fecal bacteria,
  6. Under nutrition,
  7. Measles
  8. Failing to wash hands after defecation, after handling feces or before handling food, and failing to dispose of feces (including infant feces) hygienically.


The most common etiological agents are rotavirus, enterotoxogenic E.coil (ETEC), shigella, compylobacter jejuni, cryptosporidium. Mixed infections involving two or more enteropathogens occur in 5-20% of cases.

The pathogenesis of most episodes of diarrhea can be explained by secretory, osmotic, motility abnormalities or a combination of these mechanisms. The secretory diarrhea is usually due to toxin by the organism such as toxigenic E. coli and V. cholera 01, or of viruses, such as rota virus. The toxin breakdown ATP into cyclic AMP (cAMP), which causes excess secretion of chloride and prevent absorption of sodium by the villi, resulting in net secretion of water and electrolytes (K+, bicarbonate) and purges out. Recovery occurs when the intoxicated cells replaced by healthy ones after 2-4 days.

The osmotic diarrhea can occur when the osmolality of the intestinal content become high. This may be due to ingestion of hypertonic solution or production of unabsorbable solute or maldigestion.


Shigella is responsible for 60% of all episodes of dysentery, and may cause watery diarrhea. There are four serogroups: S. sonnei, S. boydie, S flexneri and S. dysenteriae. S. flexneri is the most common serogroup in developing countries, but S. dysenteriae type 1, which occurs in regional epidemics. Ingestion of as few as 10 S. dysenteriae serotype 1 organisms can cause dysentery in some susceptible individuals. This is in contrast to organisms such as Vibrio cholera, which require ingestion of 10 to the power 8 to 10 to the power 10 organisms to cause illness.

Patients with dysentery have fever, but sometimes the temperature is abnormally low, especially in the most serious cases. Cramping abdominal pain and pain in the rectum during defecation, or attempted defecation (tenesmus) are also common. There may be fatal complication out of the dysentery due to shigella and include intestinal perforation, toxic megacolon, rectal prolapsed, convulsion, septicemia, hemolytic uremic syndrome (HUS), and prolonged hyponatremia. The major complication of dysentery is weight loss and rapid worsening of nutritional status.


Infection is established by ingestion of parasite cysts; can be killed by heating to 55°C but resistant to chlorine commonly used in water purification and gastric acidity. Upon ingestion, excysts in the small intestine to form eight trophozoites and may invade the mucosal lining. Tissue invasion occurs in 2-8% of infected individuals and most are cyst passers.

There is a colicky abdominal pain and frequent bowel movements associated with tenesmus. Stools are blood-stained and contain a fair amount of mucus. Sometimes associated with sudden onset of fever,chills, and severe diarrhea, which may result in dehydration and electrolyte disturbances.

In a few patients, ameboma, toxic megacolon, extraintestinal extension, or local perforation and peritonitis may occur. Hepatic amebiasis is a very serious manifestation of disseminated infection. Liver abscess occurs in less than 1% of infected individuals. There is fever, abdominal pain, distention, and an enlarged, tender liver. Most have a single cavity in the right hepatic lobe.

Amebic liver abscess may be associated with rupture into the peritoneum or thorax, or through skin when diagnosis is delayed.
Fresh stool samples should be examined within 20 minutes of passage and screened for motile trophozoites containing erythrocytes, for which treatment is indicated. At least three stool samples should be examined.


Lamblia infects humans through ingestion of as few as 10 cysts. Upon reaching the upper small intestine, each cyst liberates four trophozoites, colonize the lumen of the duodenum and proximal jejunum, attached to the brush border. Giardiasis is an important cause of chronic diarrhea in children. Human milk contains cytotoxic free fatty acids and secretory IgA antibodies that may provide protection to nursing infants.

The majority of individuals are asymptomatic. Symptoms develop 1-3 weeks after exposure. The most common presentation is diarrhea, weight loss, crampy abdominal pain, and failure to thrive or a sprue like illness. The onset may be abrupt or gradual; the disease may be self-limited or produce severe protracted diarrhea and malabsorption and may affect growth and development.

G. lamblia trophozoites or cysts may be found in fecal samples and Entero test is a simple method for detecting G. lamblia in duodenal fluid of children.

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