such a war will be started way before any country knows, the recent melamine scandal will be a nice clue. since we consume products that are already tainted before its found out. the long lag time to "discover" the extend of the damage would mean almost the whole population would be already affected by future poison/s added into our food supply.
worse is that rank & file doctors will be almost clueless what is going on.
mass production of tainted food may be the dawn of a new weapon of war.
*edit: our enemy may not even need to fire a bullet, just us signing surrender documents.