The mechanisms underlying the symptom of diarrhoea are based on
microbial pathogenic factors and complex host responses. The microbial
factors best understood at present are the enterotoxins and mucosal
(epithelial) invasion. Several other mechanisms, such as enteroadhesiveness,
enteroaggregation and cytotoxins, have been identified but the
sequence of events resulting in diarrhoea are not yet understood. One
problem in understanding pathogenesis has been the paucity of animal
models for acute infectious diarrhoea. Much manipulation, such as
administration of opiates or removable intestinal ties, are necessary
before an animal develops diarrhoea. Some enteric pathogens produce
non diarrhoeal illnesses in animal hosts. Salmonella typhimurium an
important agent, associated with watery diarrhoea and occasionally
dysentery, produces only an enteric fever (typhoid) like illness in mice.