Pathogenesis of diarrhea in infants and young children
On the one hand, infants’ digestive system is immature and not well-functioning, with low acidity of gastric juice, low resistance to infection and poor tolerance to food. Diarrhea can occur if they are cold, hot, eat unclean or undigested food and have fever and cold. On the other hand, the rapid growth and development of infants and young children require relatively more nutrients, and the burden on the gastrointestinal tract is heavier, which is also an important cause of diarrhea in infants and young children.
Incidence of diarrhea in infants and young children
Diarrheal disease is a common disease in children, according to relevant information, the annual incidence of diarrheal disease in children under 5 years of age in China is 201%, with an average annual incidence of 2.01 times per child per year, and its mortality rate is 0.51%. Therefore, the prevention and treatment of pediatric diarrheal disease is very important.
Etiology of diarrheal disease in infants and children
There are multiple etiologies and factors, including intrinsic, infectious and non-infectious.
1, intrinsic factors
(1) immature development of the digestive system: infants and young children, gastric acid and digestive enzyme secretion is insufficient, the activity of digestive enzymes is low, the nervous system of the gastrointestinal tract regulation function is poor, not easy to adapt to the quality and quantity of food, and rapid growth and development, the need for nutrients is relatively more, the gastrointestinal tract burden, digestive function is often in a state of tension, prone to digestive disorders.
(2) Poor defense function of the body: the immune function is relatively immature in infancy, immunoglobulin and gastrointestinal slgA in blood are low, gastrointestinal barrier function is weak, gastric acid secretion is low, gastrointestinal emptying is fast, and defense function against infection factors is poor. In addition, newborns, after birth, have not yet established a perfect intestinal normal flora, weak antagonistic ability to pathogenic microorganisms that invade the intestine, artificial feeders lack a large amount of immune substances contained in breast milk in food, and more opportunities for contamination of food and eating utensils, the incidence of intestinal infection is significantly higher than that of breastfed children.
(3) body fluid distribution characteristics: infants have more intercellular fluid, and water metabolism is vigorous, poor regulation of kidney function, prone to disorders of body fluids.
2.Infection factors
(1) Intestinal infection: mainly caused by bacteria and viruses.
(1) bacteria: In addition to the statutory infectious diseases. ① E. coli: according to its pathogenic mechanism classified as pathogenic E. coli, toxin-producing E. coli, invasive E. coli, hemorrhagic E. coli, adherent E. coli; ② Campylobacter jejuni; ③ Yersinia pestis; ④ other: Salmonella typhimurium, Proteus mirabilis, Pseudomonas aeruginosa, Klebsiella, Staphylococcus aureus, Clostridium difficile.
(2) viruses: ① rotavirus, the main cause of diarrhea in infants and children; ② norovirus; ③ enteric adenovirus; ④ others: astrovirus, cup virus, coronavirus, etc.
(3) fungi and protozoa: fungal infections are mainly Candida albicans. Some protozoan infections such as blue Giardia flagellata, colonic pouch worms, Cryptosporidium, amoeba protozoa, etc.
(2) extra-intestinal infections: children with upper respiratory tract infections, pneumonia, pyelonephritis, otitis media, skin infections and other acute infectious diseases can be accompanied by diarrhea, which is due to fever and the influence of pathogenic toxins, so that digestive disorders, enzyme secretion is reduced and intestinal motility increased.
3, non-infectious factors
The main factors are dietary factors, climatic factors and allergic factors. Improper feeding is one of the main causes of diarrhea. Excessive and premature feeding of large amounts of starchy and fatty foods, sudden changes in food varieties and weaning can all lead to diarrhea. The sudden change of climate, which increases intestinal peristalsis and decreases the secretion of digestive enzymes and gastric acid, can induce diarrhea. Some malabsorption syndromes such as lactose intolerance, glycogenic diarrhea, congenital chloride diarrhea, hereditary fructose intolerance, cystic fibrosis of the pancreas, and primary intestinal malabsorption can cause diarrhea. For those with milk protein allergy, watery diarrhea occurs 48 hours after eating raw milk.
4, pediatric prolonged and chronic diarrhea
The etiology is complex and is thought to include infections, allergies, congenital enzyme defects, immune deficiencies, drug factors, congenital malformations, etc., of which post-infection diarrhea is the most common. The results of intestinal mucosal biopsies in children with chronic diarrhea indicate that persistent damage to the structure and function of the small intestinal mucosa or impairment of normal repair mechanisms are important causes of persistent diarrhea in children.
(1) Acute infectious diarrhea is mostly transient in nature. However, acute diarrhea can turn into chronic diarrhea if the host fails to produce a normal immune response, is repeatedly exposed to infectious agents, or if the intestinal mucosa is severely damaged by infection. Most of the diarrhea is prolonged due to persistent mucosal damage, and a few are due to persistent action of the infectious agent. The thinning of the duodenal and jejunal mucosa, atrophy of the intestinal villi, increased cytoplasmic overflow and shedding of enterocytes, degeneration of microvilli and accelerated renewal of epithelial cells may be related to the adhesion of microorganisms on the surface of the intestinal mucosa. Due to insufficient time for mucosal regeneration, these new epithelial cells resemble crypt cells and are therefore hypofunctional. Decreased activity of disaccharidases, especially lactase, and brush border peptidase, combined with a decrease in effective absorption area, cause poor digestion and absorption of various nutrients. In addition, damage to the intestinal mucosa increases the permeability to pathogenic factors and macromolecular substances, sensitizing the mucosa to foreign antigens.
(2) In malnourished children, all bacteria in the upper part of the small intestine increase significantly during diarrhea, and anaerobic bacteria and yeast overgrow in the duodenum. The concentration of free bile acids is greatly increased due to the deconjugation of bile acids by a large number of bacteria. High concentrations of free bile acids have a damaging effect on small intestinal cells and also hinder the formation of fatty particles. Severely malnourished children have defective cellular immune function, secretory antibodies, reduced phagocytosis and complement levels, thus increasing susceptibility to pathogens and food protein antigens. In conclusion, persistent diarrhea predisposes to malnutrition, and malnutrition predisposes to prolonged diarrhea, which is a vicious circle of mutual causation.