Diarrhea In Children: Types Of Enteric Infections

Basic to understand - Structure of villus , Crypt of Lieberkühn, Secretory cells · Infectious, non-infectious and Osmotic diarrhea. In all of them the delicate balance between absorption and secretion gets disrupted.

Villous Cells Diagram 

• There are 2 important mechanisms to operate the absorption of Na and chloride ·  1st is known as Na- Glucose cotransport. 2 mechanism is at tip of villus cells is called Electroneutral Na-CI transport with 2 parts · They are Na+ / H+ antiport and CI - / HCO antiport. H+ 3 and HCO3 eliminated in stool. Na and CI is absorbed in intestines 

Secretory Cells in the Crypt 

• These are cells which help channel to transport Na, CI, and K into enterocytes. They have only minimal activity in resting stage. But when ↑se in cAMP in these cells it will - lead to insertion of channel into luminal membrane (CI >Na and K+), this lead to active secretion of CI- & other. into lumen.  Whenever there is active infection either is an organism present, or producing toxin or penetrating the cell. The net result can happen- At the level of absorption which leads to loss of water and stool or at the level of secretion leads to watery diarrhea.

• WHO defines diarrhea as, passage of 3 or more loose stools in 24 hours · Dysentery is presence of blood or mucus in loose stools · Nelson quotes: Dysentery is often associated with fever / tenesmus / abdominal pain but are not essential for diagnosis · Prolonged diarrhea : Any of infectious diarrhea which last for 7-13 days · Persistent diarrhea : any diarrhea which begins acutely and lasts for 14 days or longer · Chronic diarrhea : Any diarrhea in which the stool output > 10g/kg/day children >200/day for older children for more than 4 weeks or longer.

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Pathophysiology of Diarrhea 

• Broadly 2 type of diarrhea . Osmotic : due to deficiency of digestive enzyme or damage to villus structure. Secretory - normal nutrients unabsorbed, fermented food due to bacteria in gut, lead to production of osmotically active substance, pull water into lumen. Diarrhea · Therefore, in osmotic diarrhea if we restrict food and block this pathophysiology diarrhea stops. Volume of stool is comparatively less · Secretory diarrhea : In this type a toxin is produced which is responsible for active secretion of Na and chloride into lumen irrespective of fasting status diarrhea continues.

Etiology 

• Overall viral infections > bacterial in children, Mc : Rotavirus · 2nd mc of viral causes Norovirus / Norwalk virus as vaccination is high for Rota · 3rd MC is Sopovirus (family of calicivirus) Norovirus is from calicivirus family · 4th MC: Adenovirus · In Indian setup – SOPOVIRUS is relatively rare. Bacterial causes · Worldwide , ETEC > EPEC MCC · NTS- Non Typhoid salmonella is rarely seen in developing countries · EPEC is most commonly seen in 5-10 year of age · Other causes :  Shigella, NTS, Campylobacter and Vibrio cholera. Causes of dysentery · World / west MC -E.coli – EHEC / VTEC , E.coli (0157:H7) . Prevalence is decreasing · India / Asia : Shigella Dysenteric type I · Prevalence is increasing.

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Persistent Diarrhea

• Chronic Diarrhea : Mostly due to malabsorption (e.g. Celiac disease, SBS). Protozoal Causes / Parasites causing diarrhea , Giardia lamblia , Entamoeba Histolytica ,Cryptosporidium parvum, Bellantidium Coli, Isospora Belli- Occasional.

Risk Factors 

• Poor Hygiene and low Socio economic status · Pathogens transmitted by Feco – oral route ,poor drinking water, Malnutrition, lack of breast feeding. Underlying immune deficiency: PID or HIV · Vit A and zinc deficiency · Hypo / Achlorhydria : Host immunity and acid in stomach are equal important to neutralize the food which enter into the stomach, which also leads to ↑se risk of diarrhea · Pernicious anemia and H-pylori infection and excess use of PPI can lead to Hypochlorhydria and future it leads to more GI infections · Prolonged antibiotic therapy can cause ADD. Norovirus Geno group II, genotype 4 (GII 4) is the most common type of Norovirus causing diarrhea worldwide Most common types of adenovirus associated with childhood diarrhea : types 40 and 41 · Waxing and waning symptoms in childhood diarrhea : 2 pathogens.

Swimming pool exposure :  Cryptosporidium parvum (CI resistant ), Clostridium jejune · Nosocomial diarrhea – Clostridium defile · Raw or undercooked pork – Yersinia · Patterns of incubation periods - Those producing preformed toxins (staph aureus, Bacillus cereus emetic type) have a short IP of 1-6 hrs, compared to those which produce toxins in site (C perfringens, bacillus Cereus enterotoxin)- IP of 8-16 hr · Viral pathogens that attach to enterocytes and cause secretion or invasion have IP of 1-5 days while longer IP seen for protozoa or parasites due to relatively longer life cycles.

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Types of Enteric infections- Based on Pathogenic Mechanisms

Rotavirus Pathogenesis 

• Non – inflammatory type · This virus don't enter into the cell, instead NSP 4 toxin is produced which leads to activation of IP3- DAG pathway which leads to release of calcium. · Spread of infection or inflammation of adjacent cells leading to loss of water and salt.

Enterotoxin – NSP-4 · Intercellular calcium wave formation increase in release of cytokines and vasoactive substance: diarrhea · NSP-4 also causes activation of local enteric Nervous system : Direct secretion of water and Na · Pathogenesis in other toxin : mediated and inflammatory diarrhea · Toxin causes ↑ in CAMP or CGMP by activating Adenylate cyclase or Guanylate cyclase, Increase in insertion of CFTR CIChannel into luminal membrane, active CI release · Increase in CAMP also increase permeability of gut and increase leakage of Na+ / H2O · By complex mechanism there is also leakage of HCO3 in the gut. Therefore, alkaline PH of stool still present · In case of inflammatory diarrhea there is inhibition of Na /glu Co transport (SGLT-1) and inhibition of Nacl electroneutral transport caused by toxins released by inflammatory cells.

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Shigella Pathogenesis

Earliest cells affected M-cell (part of GALT / MALT in gut ) · Adjacent cells get affected which leads to apoptosis of macrophages →↑ in IL-8 levels · ↑IL-8 causes neutrophil attraction and transmigration which causes increase of inflammation and epithelial destructor · Net secretion of pus cells and mucus which leads to dysentery in Shigella.

Dyselectrolytemia in Children Diarrhea 

• Stools in inflammatory diarrhea are o Rich in K+ : → Hypokalemia in patient - Paralytic ileus - ECG changes. Usually alkaline : tendency to develop metabolic acidosis · Serum Na+: Isonatremic dehydration (50-65%), Hyponatremic dehydration  · Hyponatremic dehydration. S. Na145-150 develops when over ingestion of Hypertonic sodium Containing fluids · Here Na is more in ECF. Therefore, water flow from ICF to ECF leads to :  Cellular shrinkage and dehydration, Minimal no S/o dehydration, late signs, mortality is high here , doughy feel of abdomen.

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Hope you found this blog helpful for your Nutrition and Nutritional Disorders for NEET SS preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.