TIGERTON, July 2 -- The night before he unwittingly became the reason his six-year-old sister is alive, Nicklas Kale spent an afternoon in the backyard fashioning a sword out of wood. He had been watching Braveheart. He did not know he would use it the next day.

On June 29, while Cecilia "Cece" Kale was playing in a tree on the family's property in this Shawano County village roughly 60 miles west of Green Bay, a bat latched onto her left thigh. Her 16-year-old brother Camden spotted it and knocked it free with a pole. Nicklas, 11, ran over and killed the bat with the sword he had built the day before.

Their father saved the carcass. The family brought it in for testing. The result came back positive for rabies.

Cecilia received post-e...