Part 2 of norovirus and shellfish

The oyster is a shellfish that can be absorbed by the virus, such as found in the seawater, the bad ones, filtered and accumulate in the bodies of their own.
So, it is said that if oyster grow in a place where the sea has been polluted, and the water is clean.
Oysters, have been told to hosts like norovirus, in places where environmental pollution have proceeded, these bivalves such as oysters existence is actually very important.

Oyster is swallowed along with the large amount of sea water plankton, then, since the discharge of seawater, but should I also be discharged virus in that case, the structure of the shell, squid does not seem so.
I think I have seen a live clams and clam everyone, and have seen the moment you put a lot of water.
I will be hoarding the virus in the body because it already, that minute, when that is, water that has been cleaned.
Why, shellfish or it become the source of infection has been described and for the flow of the river earlier, the sewage, of course, a good place for shellfish grow is where there are a lot of plankton which is food.
If so, that downstream near the river that are suitable, these places are often has become a place of shellfish farming.
Based on a lot of things seem also, why norovirus, or have entered the shell, if you know why, oysters instead of bad, bad man.
So, is a non-oyster shell, Why is not there that you have accumulated in the virus as oyster?