Until about ten years ago, only a fraction of the microbial causes of human diarrhoeal diseases were known as no pathogenic bacteria and viruses could be isolated from the large majority of patients. So far, about 25 pathogenic bacteria, viruses, and parasites have been identified as causes of diarrhoea.
The well known microbial agents of universal importance that invade the intestine and cause acute diarrhoea through a variety of mechanisms are Shigellae, Salmonellae, V. cholerae, and certain strains of E. coli (ETEC, EIEC, and EPEC). The two other unicellular micro- organisms (protozoa) of world-wide distribution causing both acute and chronic diarrhoea, especially among children, are Giardia lamblia and Entamoeba histolytica.
Other conditions associated with diarrhoea include infections occurring in organs other than the intestine (e.g. measles, malaria, and pneumonia), as well as malnutrition and food intolerance.
In recent years, five groups of enteric viruses involved in childhood diarrhoea have been recognized through electron microscopy and successful stool cultures. These are rotaviruses, enteric adenoviruses, asroviruses, coronaviruses, and Norwalk viruses. In addition, a number of other infectious agents of limited or unknown importance in diarrhoeal diseases have been identified in diarrhoeal stools. Among these are Campilobacter jeujeni and Yersinia enterocolitica.
In 1982, Dr. I. de Zoysa and associates of the Ross Institute in London published a wall chart entitled A Guide to the Most Common Enteric Pathogens which provides practical information regarding each of the potential causative agents of diarrhoeal diseases.
Little information is available about the world-wide distribution of some of the newly identified diarrhoeal agents, particularly among children in developing countries, primarily because of the complexity of the diagnostic techniques. Fortunately, diagnosis of rotavirus infection can now be made by means of a simple and rapid procedure recently developed in Sweden based on assaying the antibodies in stools (enzyme-linked immuno-absorbent assay -- ELISA).
Practically all of the more common childhood diarrhoeal diseases caused by pathogenic bacteria and viruses are transmitted via the faecal-oral route. The pathogens discharged in the faeces of an infected person may enter the body of another susceptible person through the mouth. This may occur among children ingesting food or water contaminated with human excreta.
Direct transmission among persons in close contact is also possible. Such transmission could occur via unclean hands, or through contaminated objects such as bed linen, kitchen utensils, and tableware. Flies and cockroaches play a role as vectors of the infectious agents of faecal origin.
During diarrhoeal episodes, the body rapidly loses fluids together with some electrolytes that are discharged with the stools. The essential electrolytes lost are sodium (Na+), potassium (K+), chloride (Cl-), and bicarbonate (HCO3-). At the same time, the intestine may lose its capacity to absorb fluids and electrolytes taken by mouth. In mild cases, where intestinal absorption is not impaired, any fluid given orally might prevent dehydration. About 10 percent of diarrhoea episodes result in dehydration due to the excessive loss of fluids and electrolytes. Infants and young children are much more susceptible to dehydration and its consequences than adults.
It has been demonstrated that ORT involving the oral administration of glucose-electrolyte solutions can effectively restore the intestinal fluid losses, thereby counteracting dehydration in the large majority of cases. This is based on the fact that glucose enhances the intestinal absorption of water and sodium in diarrhoea patients.
Obviously then, ORT constitutes a short-term measure that can and must be adopted on a global scale to enable prompt treatment of childhood diarrhoea.
The four major strategies for controlling the transmission of the common diarrhoeal diseases are: (a) personal and domestic cleanliness; (b) hygienic food preparation and storage; (c) clean and plentiful water supply; and (d) sanitary excreta and refuse disposal.
An essential long-term objective of national diarrhoeal disease control programmes should therefore be based primarily on achieving an improvement in community water supplies and in sanitation facilities and practices. Much can be accomplished through training and health education.