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Alpha-gal allergy: the meat of the matter

Photo: Lone star tick
Credit: U.S. Centers for Disease Control

Tick that causes red-meat allergy now found in Canada

There’s a new kind of life-threatening allergy in town, and it comes with its own set of rules.

Alpha-gal allergy, also known as meat allergy or Mammalian Meat Allergy (MMA), was first reported in the literature only 10 years ago. Although meat may have been the cause of some isolated cases of anaphylaxis attributed to an unknown cause (i.e., idiopathic) reported as far back as 1985 in Australia, and the mid-1990’s in the American Southwest, no one associated those reactions with consumption of red meat (e.g., beef, pork, and lamb) at the time.

Why not?

For one, allergies to meat were rare, so it wasn’t an obvious trigger. But primarily because anaphylaxis was occurring anywhere from three to eight hours after the ingestion of meat, and skin tests were also often negative. Quite simply, no one made the connection, because anaphylaxis had never been known to work that way; most allergic reactions to foods usually take place sooner, and no food allergy known at the time had such a long, consistent gap between exposure and reaction. It also turned out to be the first known food allergy triggered by a carbohydrate rather than a protein.

It took researchers years to understand that they were confronting a whole new kind of allergy, different from anything they’d seen before. Eventually, though, they began noticing that a large proportion of the people suffering from these symptoms had also reported tick bites within the previous few weeks. Finally, two and two began to add up.

Initially, cases were clustered in specific geographic regions in Australia and the American Southwest. The Australian paralysis tick and the American lone star tick were identified as the primary culprits.

The alpha-gal molecule is a carbohydrate found in all mammalian species except Old World monkeys, apes, and humans. Alpha-gal has been shown to be in the digestive tract of at least the one type of tick. When one of those ticks bites a human, the digestive contents from the tick are introduced to the skin. In susceptible people, this may trigger the human immune system to release a flood of IgE antibodies to fight off the foreign carbohydrate. This causes the affected person to react to the alpha-gal present in all red meat – a condition which may or may not be permanent.

Aside from the delayed reactions, some symptoms are similar to those of food-related reactions, including hives, swelling, gastrointestinal discomfort, and can progress to anaphylaxis. In 70% of cases the reaction is accompanied by respiratory distress and can be particularly serious for those with asthma. In some people, alpha-gal allergy has been known to become less severe, or even disappear completely, if they avoid further exposure to tick bites.

Because the ticks associated with alpha-gal allergy are not native to Canada, the syndrome is rare in this country. However, the lone star tick has been found in Canada, as noted in this Global news article from June 2017, although reports of the tick are very infrequent.

Diagnosing alpha-gal and tips on managing

  • Don’t self-diagnose. See your doctor and ask for a referral to an allergist.
  • Not all meat allergies are due to alpha-gal allergy. An allergist will carefully diagnose an individual experiencing an allergy to meat by considering its possible causes, including alpha-gal.
  • Once diagnosed, avoid mammalian meat, and always carry your epinephrine auto-injector (e.g. EpiPen®).
  • An allergist can help you determine which foods are safe to eat and which ones may cross-react with alpha-gal.
  • Speak to a dietician to assist with the dietary replacement of B12 and iron found in meat.

To speak further about alpha-gal allergy, please contact us at info@foodallergycanada.ca.

Medical content reviewed by: Dr. Julia Upton, MD, FRCP(C) Clinical Immunology and Allergy