Why so many people are becoming allergic to meat

Tick bites are fueling the rise of allergies to the meat of mammals and everything else that comes from them.

I am 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 reach her, McGraw emails. She wants to feed me when I get there:

"Would you like to try emu?" she asks. "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.
    Wearing a wool sweater raises hives on her skin; inhaling the fumes of bacon sizzling on a stove will knock her to the ground. Everywhere she goes, she carries an array of tablets that can beat back an allergy attack, and an auto-injecting EpiPen that can jolt her system out of anaphylactic shock.
    McGraw is allergic to the meat of mammals and everything else that comes from them: dairy products, wool and fiber, gelatin from their hooves, char from their bones.
    This syndrome affects some thousands of people in the USA and an uncertain but likely larger number worldwide, and after a decade of research, scientists have begun to understand what causes it. It is created by the bite of a tick, picked up on a hike or brushed against in a garden, or hitchhiking on the fur of a pet that was roaming outside.
    Tami McGraw cannot eat any products from mammals without feeling her throat close and her blood pressure drop.
    The illness, which generally goes by the name "alpha-gal allergy" after the component of meat that triggers it, is a trial that McGraw and her family are still learning to cope with. In much the same way, medicine is grappling with it too.
    Allergies occur when our immune systems perceive something that ought to be familiar as foreign. For scientists, alpha-gal is forcing a remapping of basic tenets of immunology: how allergies occur, how they are triggered, whom they put in danger and when.
    For those affected, alpha-gal is transforming the landscapes they live in, turning the reliable comforts of home -- the plants in their gardens, the food on their plates -- into an uncertain terrain of risk.

    The allergy puzzle

    In 1987, Dr Sheryl van Nunen was confronted with a puzzle. She was the head of the allergy department at a regional hospital in the suburbs of Sydney, Australia, and had a reputation among her colleagues for sorting out mysterious episodes of anaphylaxis. This time, a man had been sent to see her who kept waking up, in the middle of the night, in the grip of some profound reaction.
    Van Nunen checked the man for the obvious irritants and, when those tests came up negative, took a thorough look at his medical history and did a skin test for everything he had eaten and touched in the hours before bedtime. The only potential allergen that returned a positive result was meat.
    Then a few more such patients came her way. There were six additional ones across the 1990s; by 2003, she had seen at least 70, all with the same problem, all apparently affected by meat they had eaten a few hours before. Groping for an explanation, she lengthened the list of questions she asked, quizzing the patients about whether they or their families had ever reacted to anything else: detergents, fabrics, plants in their gardens, insects on the plants.
    "And invariably, these people would say to me: 'I haven't been bitten by a bee or a wasp, but I've had lots of tick bites," Van Nunen recalls.
    A tick at the University of Massachusetts' TickReport laboratory.