What was one of the most deadly illness the pioneers have faced ? how was it spread?

The most deadly illness the pioneers have faced was Oregon Trail, it was spread by for hunting food, picking berries, and most of all this terrible game kids used to play that made them realize the Oregon Trail was real. It also lead up to bad fever, cholera, and dysentery.

This is the main reason of the deadly illness pioneers  had.

Hope this helps you :)

The Oregon Trail was one of the most deadly illnesses the pioneers have faced. It was spread out of control.