VIZIONS aims to understand the nature, public health importance and origins of the large number of undiagnosed infectious disease cases that occur in Vietnam, as in most other countries in the world. VIZIONS is testing the hypothesis that a significant number of these infections are zoonotic and that some will be caused by currently unrecognized and possibly newly emerging agents. VIZIONS is generating new insights into the diversity of human pathogens (especially viruses) and into the biological and behavioural processes involved in the emergence of novel pathogens.