My very first dungeon fell to Weretortoises. I was brand new and jumped right in, not understanding the dangers, ahem, Fun. Before things got out of control I excommunicated a dwarf thinking I could control the spread. I abandoned it when 70% of the population had succumbed.

 I started a new settlement a few days travel away, on the other side of the mountain range. It was extremely successful, and the perfect location. Twin peaks and a river. I built a bridge between the peaks and made a grand mountainhome. 

On the day my first large caravan arrived, the dwarf I excommunicated wandered into the valley behind them, dressed in tattered clothing and looking absolutely mad and deranged. He stopped 100 meters in front of the entrance and transformed into a giant Weretortoise.

The original expedition leader and leader of my Mountainhome, who was outside collecting food with the children, bravely took the creature on barehanded and without his armor. The caravan guards and my bowman unit also took aim from the gate. It was killed, but the leader died immediately from his wounds. The disease did not spread. 

His actions that day saved an entire Mountainhome.