NEW YORK (AP) — More than 100,000 people in the US have become allergic to red meat since 2010 because of a weird syndrome triggered by tick bites, according to a government report released Thursday. But health officials believe many more have the problem and don’t know it.

A second report estimated that as many as 450,000 Americans have developed the allergy. That would make it the 10th most common food allergy in the US, said Dr Scott Commins, a University of North Carolina researcher who co-authored both papers published by the Centers for Disease Control and Prevention.

Health officials said they are not aware of any confirmed deaths, but people with the allergy have described it as bewildering and terrifying.

“I never connected it with any food because it was hours after eating,” said one patient, Bernadine Heller-Greenman.

The reaction, called alpha-gal syndrome, occurs when an infected person eats beef, pork, venison or other meat from mammals — or ingests milk, gelatin or other mammal products.

It’s not caused by a germ but by a sugar, alpha-gal, that is in meat from mammals — and in tick spit. When the sugar enters the body through the skin, it triggers an immune response and can lead to a severe allergic reaction.

Scientists had seen reactions in patients taking a cancer drug that was made in mouse cells containing the alpha-gal sugar. But in 2011 researchers first reported that it could spread through tick bites, too.

They tied it to the lone star tick, which despite its Texas-themed name is most common in the eastern and southern US (About four per cent of all US cases have been in the eastern end of New York’s Long Island.)

One of the studies released Thursday examined 2017-2022 test results from the main US commercial lab looking for alpha-gal antibodies. They noted the number of people testing positive rose from about 13,000 in 2017 to 19,000 in 2022.

Experts say cases may be up for a variety of reasons, including lone star ticks’ expanding range, more people coming into contact with the ticks or more doctors learning about it and ordering tests for it.

But many doctors are not. The second study was a survey last year of 1,500 US primary care doctors and health professionals. The survey found nearly half had never heard of alpha-gal syndrome, and only per cent said they felt very confident they could diagnose it. Researchers used that information to estimate the number of people with the allergy — 450,000.

People with the syndrome can experience symptoms including hives, nausea, vomiting, diarrhoea, severe stomach pain, difficulty breathing, dizziness and swelling of the lips, throat, tongue or eye lids. Unlike some other food allergies, which occur soon after eating, these reactions hit hours later.