What to know about the life-threatening meat allergy caused by tick bites

A largely unknown illness caused by tick bites can cause a life-threatening meat allergy. Here is what you need to know. Ticks are known for transmitting infections that can cause serious illnesses, including Lyme disease and tick-borne encephalitis. However, they are also responsible for a lesser-known condition: alpha-gal syndrome, a life-threatening meat allergy. First linked to a particular species of ticks about 15 years ago, the syndrome is being diagnosed more frequently as awareness grows and more people report allergic symptoms after eating meat and, in some cases, dairy. The allergy does not impact consumption of seafood or poultry, chicken, turkey and eggs. What causes it? Unlike other tick-borne illnesses, alpha-gal syndrome is not caused by a bacteria or a virus. It occurs when the human immune system triggers an allergic response to a type of sugar known as alpha-gal, which is short for galactose-α. This sugar is found in the meat of most mammals, such as cows, pigs and sheep, and in the saliva of certain ticks, but not in humans or other primates. When consumed, it is normally harmless. However, when ticks carrying it bite through the skin, they can introduce it directly into the bloodstream, prompting the development of antibodies in humans — immune system proteins that fight off foreign invaders — which learn to identify and attack alpha-gal sugar molecules. Afterwards, when humans consume mammalian meat, the alpha-gal antibodies can trigger an allergic reaction. “It turns out that the skin is a fantastic way to make an allergic response," said Dr Scott Commins, an alpha-gal syndrome researcher at the University of North Carolina. "If this all happened orally, and we were eating alpha-gal like we do with steaks or barbecue, then we wouldn't become allergic.” What are the symptoms? One characteristic feature of alpha-gal syndrome is that symptoms may not appear until up to six hours after consuming red meat. It can take weeks or months for the condition to develop, with the severity often worsening over time. “The patient may have had meat in the evening and then woken up at night with severe symptoms. This makes it difficult, for both the patient and doctor, to link the allergic reaction to something that was ingested hours before,” said Marianne van Hage, professor of clinical immunology at Karolinska Institutet in Sweden. Symptoms can include a rash, widespread itching, gastrointestinal problems such as bloating and abdominal discomfort, and anaphylaxis or swelling, difficulty breathing and shock. Are more people being diagnosed with alpha-gal syndrome? Although reports of the illness are rising, experts attribute part of that increase to greater awareness among health professionals and the public. “I think part of it is more people have learned about it and are on the watch for this syndrome,” said Maria Diuk-Wasser, a Columbia University researcher who studies tick-borne diseases. Rising numbers also reflect the expanding habitat range of the Lone Star tick, the primary vector, which is currently confined to North America. Other species, such as Ixodes ricinus — the sheep or deer tick in Europe — can also be associated with alpha-gal syndrome, though less frequently. How is it diagnosed? Alpha-gal syndrome is diagnosed through a blood test that looks for the antibody IgE. “The blood test in and of itself is great, but you can’t rely on that just for diagnosis. You need the actual symptoms too," Commins said. “In the allergy world, we have a lot of trouble with false positives on blood tests. In some patients, the allergy can fade after several years. Commins has observed this in about 15% to 20% of his patients. Even so, avoiding further tick bites remains essential to preventing a recurrence.