How does a fleas-on-rats disease get weaponized? Aerosol? Infect suicide-bomber types and have them infect others?
Yes. If you aerosolize plague, you inhale it and develop pneumonic plague, and that has a much higher death rate than bubonic plague, which develops from entering the bloodstream.
Aerosol is right. There is bubonic plague (transmitted by rats) and pneumonic plague (transmitted through the air). Pneumonic plague is almost 100% fatal without treatment. An infected person has pneumonia and infects others with droplets spread by coughing. An epidemic can be created with an aerosol bomb exploded at the right altitude. If the organism is bioengineered to be resistant to antibiotics, you have a potent weapon.
There are two problems: (1) as with any bioweapon, you risk killing some of your own side; and (2) constructing a bomb that explodes at the right altitude, creates aerosol droplets of the right size, and doesn't kill the organism is a problem.