What is Alpha Gal, the Red Meat Allergy Tied to Tick Bites?

It’s bad enough that ticks are transmitting Lyme disease and Rocky Mountain spotted fever.

Now there is growing evidence that cases of a potentially life-threatening meat allergy linked to the bite of the lone star tick are on the rise.

Called alpha-gal syndrome, it causes an allergic reaction to the consumption of red meat products including beef, lamb and pork, says Trenton Honda, an environmental epidemiologist and clinical professor at Northeastern’s Bouvé College of Health Sciences.

AGS is associated with the bite of the lone star tick, but unlike allergic reactions to bee stings, symptoms don’t usually emerge until two to six hours later, Honda says.

“You can imagine that would complicate the ability to identify the offending agent,” says Honda, who is also a physician assistant.

Reactions can range from life-threatening anaphylaxis to hives, nausea and symptoms resembling irritable bowel syndrome, he says.

He says he talks about alpha-gal with his students at Northeastern, but adds that many health care providers are unfamiliar with AGS and don’t know how to test for it.

“It’s an emerging condition. There’s no surveillance so we don’t know how many people are actually suffering,” Honda says.

The Centers for Disease Control and Prevention says that more than 110,000 suspected cases were identified between 2010 and 2022.

But the CDC added that more research and data is needed to understand the full extent of AGS in the population.

People who are allergic develop antibodies to a carbohydrate molecule called galactose-alpha-1,3-galactose, aka alpha-gal, found in the blood of non-primate mammals including cows, deer, goats, pigs and sheep, Honda says.

Lone star tick range expanding

AGS is associated with the bite of lone star ticks, but the CDC says other ticks also may be implicated, he says.

“Alpha-gal is expressed in the saliva and gastrointestinal tracts of lone star and other ticks, and humans — who as primates do not express this molecule in their tissues — develop allergies triggered by alpha-gal when they are exposed to the molecule in subsequent tick bites or through ingestion of meat that contains alpha-gal,” Honda says. 

Lone star ticks are traditionally associated with Southern states and Texas, but their range is expanding northward to New England and even Canada.

Larry Dapsis, entomologist for the Cape Cod Cooperative Extension, says in Massachusetts there are established lone star tick colonies on Sandy Neck Beach Park in Barnstable as well as on Martha’s Vineyard, Nantucket and the Elizabeth Islands.

Veterinarians in other areas of Massachusetts have reported pulling lone star ticks off dogs and other pets, Dapsis says.

“Ecologists think it’s another sign of climate change. Plants and animals are moving to different places where we didn’t use to see them before,” he says.

AGS can cause serious illness, Dapsis says.

“I met one person who said his dad came to a family barbecue and had a burger. Four or five hours later he went into anaphylactic shock. He was in a hospital in a New York minute. Couldn’t breathe.”

The CDC posts a long list of possible allergic reactions, including hives or itchy rash; nausea or vomiting; heartburn; diarrhea; cough; shortness of breath; difficulty breathing and a drop in blood pressure.

Those afflicted with AGS may also experience swelling of the lips, throat, tongue or eyelids or dizziness and faintness after consuming mammalian products.

Watch out for hidden triggers

Some AGS sufferers find relief by avoiding red meat, but individuals with severe cases may also be triggered by products containing gelatin and dairy, Honda says.

Even some medical products, such as heart valves from pigs or cows as well as monoclonal antibodies and heparin, may contain mammalian byproducts that cause allergic reactions in sensitive individuals, Honda says.

He says AGS was first identified after people began having reactions to a new monoclonal antibody cancer treatment in 2004. 

The culprit was identified as alpha-gal, which is present in all mammals except humans and some other primates. 

AGS has now been found all over the world, although the full extent of the condition is not known due to lack of surveillance and mandated reporting, Honda says.