It's helpful to know the strange facts about viruses. They are not truly alive for they cannot multiply without hijacking the reproductive machinery of a cell. They are not living in the sense required by evolutionary theory to work. For that reason, they could not have been precursors to cells. Some single cells ARE living creatures in their own right, like bacteria or amoeba. Others function together in multi-cellular organisms such as plants and animals. But viruses can only function and reproduce if they can force their way into a living cell to use the cell's system to replicate itself.
It is scientifically maintained that viruses arise from degeneracy in living cells. That would mean God did not create viruses because all the life forms that He created were good. Degeneracy only began once humanity decided to do things the way a degenerate spirit form led them into believing was truth. It wasn't. Instead of the 'higher life' it promised humanity, going his way resulted in degeneracy, then death. Satan has corruptive, degenerating powers, and viruses only arise with degeneration in cells, then depend on the cell's ability to replicate to spread themselves. Viruses are not technically alive, in their own right. They are corruptions and sin has corrupted all of God's good creation.
All I would add is that God had everything in place at the start, to be utterly balanced and harmonious, with no disease, until a nasty piece of work came along to put a spanner in the works, and corruption entered in, affecting all creation. God has allowed that - to a degree, and for a purpose - but will restore everything to perfect balance and harmony, with no disease.