The Human Virome Program will analyze samples from thousands of volunteers in an effort to understand how viruses affect health.
A mumps virus enters the body, then enters a cell. There it makes copies of itself. How does the immune system respond? It's up to you to figure it out. A play-by-play explanation will follow ...
In both of those cases, virus samples showed that once it was in the body, it mutated in ways that would allow it to stick to cells in the mucous membrane lining the upper respiratory tract.