As far as we know, virus can grow and re produce only in living tissue. This mean it is impossible to cultivate them away from living tissue, and makes it difficult to study their growth habits. That is why they are classified by their ability to infect living cells and by the reaction they produce in the body of animals or humans
Does the virus produce a poison or toxin ? It is now believe that they do produce toxins, but the toxin and the virus cannot be separated. We still do not know how these toxins produce disease if they do