I'm going to stop you at the most highly advanced biological agents the world has ever seen... not even close. The US is working on nano-scale (weaponizing prions etc). Let's face it, in a BIO versus NUKE war... the US wins hands down (if you call it a win, everyone loses)

First of all before the "24" jokes go flying, prions are very real, they are the non-biological component of mad cow disease and are highly infectious.