Viruses and diarrhoea - where are we now?

Viruses are important causes of diarrhoea, with the major mortality occurring in the poor tropical overcrowded parts of the world. A successful vaccine, to rotavirus at least, may be developed, but how widely it would be used is uncertain. Even if successful, it would not remove all virus-associated diarrhoea and vomiting any more than a successful influenza vaccine would remove all viral respiratory disease. Perhaps the one aspect that needs most attention is the host. It is evident that not all infections lead to disease and that this is not simply related to the amount of virus in the faeces. This could be an indicator of the amount of damage--more virus coming from more infected cells--but there appear to be similar amounts of virus in "normal" stools as in diarrhoeal ones. Why is it then that some host, some babies, and not others have diarrhoea and vomiting? Is there an important, and as yet unrecognized, difference? If there is and it can be identified, then finding how to induce it or increase it in young babies could be as effective as a vaccine.