They barely explained the capabilities because it was out of scope for the manga. On the practicality side, however, this type of "munition" would be utilized the same as any other urban or metropolitan sphere bioweapon, insidious, difficult to purge, a constant hazard like leftover landmines, salted earth but not irradiated.
Biological agents basically are a terror weapon used against the enemy rear areas - already because deploying them anywhere near the frontlines would be a really great way to inevitably infect your own troops and nobody wants that. Makes you wonder about the delivery method though, these things seem a mite large to smuggle into the target area like you can with pathogens and I rather doubt they'd survive ingress by missile...
There was probably a kill switch originally but I got the distinct impression several things went badly, maybe due to espionage.
More likely projections on the actual effectiveness and survivability in the wild of any built-in killswitch features there might have been were wildly over-optimistic, possibly combined with reckless removal of such safety and/or excessive deployment by the makers as a final fuck-you gesture should the war have gone down the drain for them - the kind of regime that might develop and actually deploy this kind of rather baroque terror weapon strikes me as the kind also predisposed to picking fights with overwhelmingly powerful coalitions due to badly impaired leadership judgement, and sufficiently petty and unhinged to try and DELETE FUCKING EVERYTHING once it becomes indisputably apparent they're going to get their shit pushed in hard.
Compare the attempted national self-immolations by the Nazis (and their increasingly gratuitous efforts to level London with a succession of V-weapons) and the hardliners in the Imperial Japanese regime in '45, and both distinctly pettily taking out their frustrations on unfortunate prisoners still in their clutches... not hard to imagine fictional radical regimes starting to undiscriminately throw whatever weird unpleasantness their R&D boffins might have managed to cook up at the enemy once defeat becomes inevitable.
