Alpha-gal Syndrome: The Meat Allergy Caused by a Tick

By: Jesslyn Shields  | 

tick meat allergy
A bite from the lone star tick (Amblyomma americanum) can trigger an allergic reaction to the consumption of red meat. Yikes. Lisa Zins/Flickr (CC BY 2.0)

Food allergies are a bummer, but for meat lovers, alpha-gal syndrome (AGS) — or mammalian meat allergy (MMA) — is kind of a tragedy.

Alpha-gal (galactose-α-1,3-galactose) is a sugar molecule found in most mammals, but not in humans — and not in fish, birds or reptiles. Scientists in the U.S. first began seeing allergic reactions to red meat in the 1990s, which they traced specifically to alpha-gal by 2006. By 2012, cases had been confirmed in 39 states. Cases were also popping up in Australia.

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Alpha-gal syndrome causes a mild to severe allergy to the meat of mammals such as cows, pigs, sheep, rabbits, deer and others, as well as mammal products, like gelatin and dairy. Its symptoms include a lot of the usual allergy symptoms — hives; runny nose; nausea and vomiting; swelling of the eyelids, lips, throat and tongue; shortness of breath and possibly anaphylaxis, a severe, body-wide allergic reaction. But people don't just come down with AGS for no reason. It may surprise no one that it's just the most recent indignity brought on by the insect that seems to ruin everything it touches: the tick.

It took scientists a few years to discover how exactly people were becoming allergic to meat, but by 2009, they narrowed the cause down to the bite of the lone star tick (Amblyomma americanum), discovered by a scientist who noticed the map of the cases of alpha-gal allergy overlapped almost perfectly with the distribution map of the tick, which lives in much of the eastern U.S. and Mexico. Lone star ticks look very much like any other North American tick, except the females have a white spot — sometimes shaped a bit like a star — on their backs. In Australia, alpha-gal sensitivity has been linked to the hard-bodied paralysis tick (Ixodes holocyclus).

In order to develop a sensitivity to alpha-gal, a tick must attach to you only long enough to leave a bite mark and inject alpha-gal into the skin. After that, the immune system takes over, releasing immunoglobulin E (IgE) antibodies that trigger the release of histamines to fight off the alpha-gal sugar, which you ingested with that steak you ate for dinner, and which your immune system has deemed dangerous. One unusual thing about an alpha-gal allergy is that the allergic reaction might not kick in for three to four hours after eating red meat, so it can be one of the more difficult allergies to trace to the source.

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