Thousands of people are developing life-threatening reactions to animal products – and a single tiny creature is to blame.

It was early morning in early summer, and I was tracing my way through the woods of central North Carolina, steering cautiously around S-curves and braking hard when what looked like a small rise turned into a narrow bridge. I was on my way to meet Tami McGraw, who lives with her husband and the youngest of their kids in a sprawling development of old trees and wide lawns just south of Chapel Hill. Before I reached her, McGraw emailed. She wanted to feed me when I got there.

“Would you like to try emu?” she asked. “Or perhaps some duck?”

These are not normal breakfast offerings. But for years, nothing about McGraw’s life has been normal. She cannot eat beef or pork, or drink milk or eat cheese or snack on a gelatine-containing dessert without feeling her throat close and her blood pressure drop.