(brb writing a novel about a secret agent trying to stop a terrorist vegan organization from putting this in the water supply of new york city.)
That don't produce alpha-gal, the glycan that generates this allergy.
If humans produced alpha-gal, negative selection would typically remove it as a possible ligand, and this would rarely happen.
You've got bizarre disease states, immunobiology (a vast field in its own right - B cells, immunoglobulins, antigens, amplification, negative selection, etc.), evolution, and even ecology.
Just in this one problem.
Wasn't as straight forward as you might think to diagnose.
https://www.cbsnews.com/news/kris-kristofferson-misdiagnosed...
It turned out after quite some time that she had lyme disease, and once that was treated, she basically hit her growth spurt with back interest. It was honestly surprisingly how much of a change it made. She grew much taller, and now has a very active career as a musician and social activist, barely ever sitting still for very long.