Introduction
Acute diarrhea could be defined as excess stool water (greater than 10 mg/kg/day in infants) with loss of electrolyte , during less than 14 days.
Diarrheal diseases are a leading cause of childhood morbidity and mortality
in the developing world , although most of the episodes in infants are
self-limited. According to World Health Organization (data from 1988) approximatly
four (4) million children less than 5 years of age in Asia, Africa, and
Latin America die anually from diarrhea; and 80% of these deaths occur
in the first 2 years of life.
Mechanisms of Diarrhea
The small bowel absorbs the greatest volume of water an the colon concentrates intestinal contents against a high osmotic gradient. The absorption of fluid in the small intestine is higher than in colon; so disorders that interfere with absorption in the small intestine tend to produce voluminous diarrhea,whereas disorders compromising colonic absorption produce lower volume diarrhea.
The basis of all diarrhea is disturbed intestinal solute transport ; water movement across intestinal membranes is passive and is determined by both active and passive fluxes of solutes, particularly sodium,chloride, and glucose. The pathogenesis of most episodes of diarrhea can be explained by secretory,osmotic , or motility abnormalities:
Secretory: Decreased absorption and increased secretion,caused
by accumulation of cAMP or cGMP.This accumulation is often caused by a
secretagogue, such as cholera toxin,E.coli toxin. The stool tends to be watery and of large volume,with a normal osmolality.
Osmotic: Occurs by ingestion of unabsorbable solute ,
digestive enzyme deficiency or transport defects. This form of diarrhea
is usually of lesser volume than a secretory diarrhea and stop with fasting.
Stool osmolality is greater than 50 mOsm.
Motility abnormalities:
· Rapid transit - associated with
irritable bowel syndrome.
· Delayed transit - associated with
bacterial overgrowth.
Etiology of Acute Diarrhea
The diarrhea could be:
(1) Infectious
(2) Non-infectious
(1) Infectious diarrhea
There is a wide variety of enteropathogens that causes diarrhea,including bacteria,viruses, and parasites. The acute infectious diarrhea could be inflamatory or noninflamatory:
· Noninflamatory- caused by enterotoxin
production by some bacteria , destruction of villus (surface) cells by
viruses, and adherence and/or translocation by bacteria.
· Inflamatory - there is direct intestine
invasion or citotoxins production by bacteria.
The main mechanism of transmission for diarrheal pathogens is fecal-oral,with food and water being the vehicles for most episodes.Enteropathogens like Shigella, Giardia lamblia or enteric viruses, that are infectious in a small inoculum,may be transmitted by person-to-person contact.
® Factors that increase susceptibility to infection with enteropathogens:
The relative importance and epidemiologic characteristics of diarrheal pathogens vary by geographic location. (see table 1 )
| United States (%) | Developing countries (%) | |
| Viral | ||
| Rotavirus | 8-50 | 4-45 |
| Enteric adenovirus | 5-15 | 5-15 |
| Norwalk agent | 5-15 | 1-2 |
| Pestivirus | < 10 | * |
| Astrovirus | 1-5 | * |
| Calicivirus | 1-2 | * |
| Coronavirus | < 1 | |
| Bacterial | ||
| Campylobacter jejuni | 1-7 | 1-7 |
| Salmonella | 2-4 | 0-15 |
| Enterotoxigenic E.coli | 1-4 | 7-50 |
| Enterohemorrhagic
E.coli |
1-3 | * |
| Shigella | 1-3 | 3-16 |
| Yersinia | 1-3 | * |
| Clostridium difficile | 1-2 | * |
| Aeromonas | < 1 | * |
| Pleisomonas | < 1 | * |
| Vibrio cholera and
other species |
1-6 | |
| Parasitic | ||
| Giardia | High | 4-20 |
| Cryptosporidium parvum | High | 4-8 |
| Entamoeba histiolytica | < 1 | 2-15 |
| Dientamoeba fragilis | < 1 | * |
| Balantidium stercoralis | < 1 | * |
| Strongyloides stercoralis | < 1 | * |
| Food Poisoning | ||
| Staphylococcus aureus | 1 | * |
| Clostridium perfringens | 1 | * |
| Bacillus cereus | < 1 | * |
· Viral Enteropathogens
Enteroviruses destroy villus cells enterocytes, leading to diarrhea; that is usually associated with fever,vomiting and respiratory manifestations.The main viral agents are Rotavirus, Enteric Adenovirus and Norwalk agent. In Brazil, Rotavirus is the major causative agent of infectious diarrhea in infants ; affecting prefencially sucklings (6 to 24 months).The mechanism of transmission is fecal-oral.
· Bacterial Enteropathogens
Toxin-producing bacteria (Enterotoxigenic E.coli [ ETEC] , S.Aureus, Bacillus cereus , C.perfringens) disrupt the normal absorption and secretory process in the small intestine , causing a watery, nonbloody diarrhea associated with bloating , nausea , or vomiting ( noninflamatory diarrhea).
The presence of fever and bloody diarrhea (dysentery) indicates colonic tissue damage caused by invasion ( Shigellosis, Salmonellosis, Campylobacter) or a toxin ( C.difficile , E.coli 0157:H7) --- Inflamatory diarrhea. Because these organisms involve predominantly the colon, the diarrhea is small in volume. Fecal leucocytes are present in infectious with invasive organisms.
· Parasitic Enteropathogens
The major parasitic enteropathogens are Giardia lamblia , Cryptosporidium parvum and Entamoeba histiolytica. In Brazil, Ascaris lumbricoides and Strongyloides stercoralis have a high prevalence.
In developing countries ,where the incidence of parasitic infections is significant (mainly in emaciated children), the patients must have their stools examined for ova and parasites. Examination of more than one stool specimen may be necessary to stablish a diagnosis.
In developed countries , as United States of America , the examination of patients stool specimen must be required if there is a history of recent travel to an endemic area , negative stools cultures for other enteropathogens , persistent diarrhea, or if the patient is immunocompromised.
(2) Noninfectious diarrhea
There are many noninfectious causes of diarrhea; including:
- Feeding difficulty
- Anatomic defects --- malrotation, intestinal duplications, Hirsprung disease, short bowel syndrome, microvillus atrophy.
- Malabsorption -------- Disaccharidase deficiencies, pancreatic insufficiency , cholestasis , celiac disease.
- Endocrinopathies ------ thyrotoxicosis , Addison disease.
- Food poisoning --------- heavy metals , mushrooms.
- Neoplasms -------------- neuroblastomas , ganglioneuromas , Zollinger-Ellison syndrome , vasoactive intestinal peptide syndrome.
- Miscellaneous ----------- milk allergy , Crohn disease , ulcerative colitis , laxative abuse , motility disorders.
Bibliography
1. Nelson, Waldo e. ; Behrman,Richard E. ; Kliegman,Robert M.;Arvin,Ann M.; Textbook of Pediatrics; 15th edition; 1996;W.B.Saunders Company.
2.Bhattacharya SK et al. Risk factors for development of dehydration in young children with acute watery diarrhoea : a case control study. Acta Paediatr 84:160-4,1995.
3.Mehta DI, Lebenthal E. New developments in acute diarrhea. Current Problems in Pediatrics 24: 95-107,1994.
4.Sabrá,a. et al; Tubo digestivo em Pediatria; 1996; Editora Cultura Médica.
5.Rotinas de pediatria I - IPPMG; 2 edição;1995;Editora Cultura médica.
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