How viruses multiply

Viruses work differently. We won't go into it in any detail, but they depend on the body's own cells to reproduce. That's one of the reasons why the symptoms of a virus infection take longer to show up than from a bacterial infection.
     Of the six nasty little pathogens we are looking at, three of them, listeria, Hepatitis A, and Norwalk-type, are viruses. All viruses can be killed off by cooking food to at least 160°F or by boiling the water used for cooking. (The water is a likely way that viruses spread.)