If viruses could synthesize chemicals in the body I think that opens up a lot of interesting gameplay with mechanics that are already established in the game.
Transferring virus effects into reagents would also mean the adding of interesting negative chemicals that arent jsut sarin gas or some other neurotoxin. It would also allow, similar to botany, the ability to attach unique reagents/chemicals to a department/job. Using Monkeys with specific viruses to synthesize chemicals for extraction via dialysis would add, if nothing else, more things for the virologist to do.