Lessons from diarrheal diseases: demography to molecular pharmacology

From diarrheal diseases come profound lessons about health and population growth, microbial pathogenesis, and the molecular pharmacology of signal transduction. Epidemics such as cholera, hemorrhagic colitis, salmonellosis, and cryptosporidiosis remind us of how interdependent we are, sharing enteric microbial flora on a global scale. Diarrhea morbidity and mortality teach us that disease and poverty do not control but are associated with population overgrowth. Great advances are being made in understanding new bacterial, viral, and parasitic causes and treatment of diarrhea, especially persistent diarrhea. In addition, microbial toxins provide unique pharmacologic tools to probe cell signaling pathways. The mechanism of action of cholera toxin, once thought so clear, now appears to involve additional pathways such as platelet-activating factor and prostaglandin synthesis. Escherichia coli ST has opened a whole family of activators of guanylate cyclase, including new mammalian products that regulate sodium transport. Clostridium difficile toxin A provides a novel tool to dissect mediators involved in inflammatory diarrhea. These lessons have both basic implications for science and practical applications for medicine and society.