Pneumonic+plague

Pneumonic plague was the more virulent and more lethal strain of the Black Death; it spreads via airborne droplets, which meant that unlike bubonic plague, where one was relatively safe so long as one studiously avoided contact with anything an infected victim might have touched (and even second and third degree contact), one could contract pneumonic plague merely by standing in proximity to a victim. This led to widespread flight from population centres and quarantines, which in turn led to the collapse of some social structures, such as, in some cases, organized clergy, when the leading religious men also fled the towns.