Mystery Allergy Strikes Adults

Long-held views upended

Last year, the Virginia team published a study in the Journal of Allergy and Clinical Immunology detailing the cases of 24 adults, including Quinn, who had developed a sudden meat allergy. Eighty percent reported being bitten by ticks weeks or months before the allergy appeared. Many had experienced anaphylaxis as much as six hours after eating red meat, a highly unusual occurrence because food allergies typically cause violent reactions in less than 30 minutes. Similar findings were reported in the Medical Journal of Australia by a team of Sydney allergists.

So how does a tick bite trigger a sudden allergy to meat? Scott Commins, an assistant professor of medicine and lead author of the U.Va. study, said that in susceptible people such as Quinn, a tick bite that causes a significant skin reaction seems to trigger the production of an antibody that binds to a sugar present on meat known as alpha-gal.

When a person who has the antibody eats meat, that triggers the release of histamine, which causes the allergic symptoms: hives, itching and, in the worst case, anaphylaxis.

But many questions remain and are the subject of ongoing research, said Platts-Mills, who has the problem himself. (An avid hiker, he suffered numerous bites from ticks that had nested in his hiking boots.) His lab has collected data on more than 300 patients from the United States and abroad and has become a referral center for suspected cases.

"We're sure ticks can do this," he said. "We're not sure they're the only cause." Nor do researchers know why anaphylaxis is so delayed or why only some people develop a problem after tick bites. They do know that the allergic reaction is dose-related. Eating a small amount of meat probably won't cause a serious problem; a large steak will. Attacks can be unpredictable and don't occur every time a susceptible person eats red meat.

Commins said researchers have also observed that people with certain blood types appear to be more at risk. Those with the rarest types—B and AB—do not appear vulnerable, because elements in their blood are chemically similar to alpha-gal.

Climate also appears to play a role: Blood samples from Boston and northern Sweden almost never reveal alpha-gal antibodies, which are common in samples from patients in Virginia, North Carolina and other Southern states, as well as in southern Sweden and parts of Australia—all areas that do not experience hard freezes that kill ticks.

In Quinn's case, testing revealed that she had type A blood and exceptionally high levels of the antibody to alpha-gal. Because there is no treatment for the allergy, she cannot do much except to avoid beef, lamb and pork—or anything cooked with them.

Remember that episode in Tulsa? Quinn later discovered that the steak fries she had eaten at dinner had been prepared in oil previously used to fry beef.

She said she now asks about how a food is prepared when she eats out, and is trying to adjust to life without her favorite food.

"This changes your life tremendously," she said. "I'd love a good steak."

Sandra G. Boodman writes about medicine and health for the Washington Post and Kaiser Health News.