I heard on the radio a few days ago1 a discussion on viruses and diseases (go figure why :)).
The guest was very precise in how the virus enters a cell, how its RNA merges with the cell's one and how it turns the cell into a "virus factory" (roughly speaking).
The question which was not accurately answered was "and so what? how does this makes someone actually sick?"
One of the points vaguely confirmed by the virologist (following a question from the journalist) was that the immune response of the body (notably the raised temperature) was what we perceived as the disease.
Since their time was short, there were no more deliberations on that interesting point.
My question: what happens that turns the "virus replication" activity into disease? I understand that the raised temperature is a direct effect of the immune system fighting these foreign bodies (the virus) but there are other effects such as headache, cough, etc.
Are all of these a consequence of the immune system fighting back? Or is the virus changing the way the cells function, and therefore they fail at their intended activity?
1 French radio France Culture, the guest was Olivier Schwartz, director of the Dept of Virus and Immunology of the Institut Pasteur, link to the podcast (in French, obviously)