FtA: Fungus!

Rasher shook his head and spat on the ground - the whole town would have to go.  Peering through his binoculars, he looked down into the town square.  At first, it looked like a town meeting, with a single figure standing at the center, and a crowd facing him.  It was only if you looked closely that you could see the telltale signs - they were all puffy and fat, far from normal in this part of the world.  The swaying was what gave them away, though.  Silently, they swayed, as if blown by some breeze, back and forth, back and forth. 

Bloaters, definitely.

Suddenly the swaying stopped, and as one, they all turned and looked directly at Rasher.  He felt a tug on his leg and looked down to find that tendrils had climbed halfway to his waist.  He screamed, ordering his men to open fire, and was shocked when they turned their flaming arrows upon him. 

"I'm not infected yet!  I can cut off my..."

His squad cut him down without hesitation.  Grenger, his second in command, bent and picked up the binoculars.  "Come on, men, there's work to be done."

Some time after the fall of civilization, a species of fungus, Ophiocordyceps unilateralis, evolved beyond creating zombie ants, and started attacking higher species with more complex brain patterns. As it evolved, so to did its use of those that it infected. 

Driven by a need for propogation, the fungus infects its hosts, and eats away at the soft tissue, giving the victim a distended appearance, and giving rise to the name of the infection, the Bloat.  Rather than driving them to high places, however, they drive them to populated areas, where their bodies expel the spores from the body's orifices.  Most of the time this happens violently, with the pressure even ripping the bodies open in some cases, and infecting all who are near.  Sometimes, though, there is a gradual release, and a host can walk around for days, infecting everyone he breaths on or touches.  The Bloat lives mainly underground, and is a fierce enemy of the Ant Kingdom, who will sacrifice themselves to force the infected away from their colony, and use slaves to burn infected areas of the underground. 

Every once in awhile, though, someone ventures into the wrong cave and brings the Bloat back to town.  Surrounding villages will act swiftly and without mercy to contain an outbreak of the Bloat, and will burn whole swaths of land to prevent it from spreading.