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Alpha-Gal syndrome—when tick bites can make you allergic to a sugar in red meats
Most commonly when people are allergic to something, it is the protein that causes the allergy. Contrary to myth, sugars typically do not cause allergic reactions, rather they can contribute to different issues such as food intolerances and sensitivities.
There is an often-misdiagnosed, yet emerging syndrome called Alpha-Gal Syndrome (AGS) where people can become allergic to a specific sugar in red meats and other animal food products and the cause of this allergy comes from tick bites. A recent study by the Centers of Disease Control and Prevention (CDC) showed up to 450,000 people in the U.S. may be affected and that number is rising.
What makes AGS unique?
AGS is different from most food allergies because the person becomes allergic to a sugar, galactose-alpha-1,3-galactose not a protein which is the most common issue. This alpha-gal sugar is present in the meat of most mammals but not humans, birds, fish, or apes. Ok, so where do the ticks come into play? I’m so glad you asked. Lone star ticks transmit alpha-gal through their bite and some patients develop allergic antibodies to the sugar which cause an allergic reaction the next time the person eats the meat of mammals, such as beef, pork, and lamb. People can also be exposed through gelatin or a host of other mammal-based products.
Other unique features include the symptoms, timing of symptoms, and how patients present to the doctor. Allergic reactions can range from mild to severe and include symptoms of abdominal pain, diarrhea, nausea, hives, swelling, and even anaphylaxis. Some patients may only have isolated gastrointestinal symptoms. Unlike most food allergies, which cause reactions within minutes after eating, AGS usually doesn’t appear until two to eight hours after exposure. So, it is a more delayed reaction. You can develop alpha-gal syndrome even if you’ve never had food allergies before. All these factors make it an elusive diagnosis for many clinicians. Even if doctor has heard of AGS, they may not know how to diagnose it.
Which foods contain alpha-gal?
- Meat and products made from mammals
- Beef, pork, lamb, venison, rabbits
- The organs of these animals contain higher amounts of alpha-gal
- Medications or medical products containing mammal products (such as cetuximab)
- Gelatin—attention paid to medical products with special caution taken with parenteral administration of bovine or porcine gelatin containing medical products as that can cause anaphylaxis to AGS patients even if gelatin tests are negative.
- Lard
- Meat broth, stock
- Milk contains alpha-gal, but many patients can tolerate milk
Which foods do NOT contain alpha-gal?
- Seafood
- Poultry
- Eggs
How is alpha-gal syndrome diagnosed?
Like any allergy diagnosis, it starts with a detailed history. In a test-oriented society, the conversations that allergists have with patients are the most important piece of the diagnostic puzzle. History of possible tick exposure or bites is critical and the timing of the symptoms after the trigger exposure as described above.
Patients should be referred to an allergist for testing as the correct tests need to be conducted and those tests need proper interpretation based on the history. Blood tests can confirm the diagnosis by measuring alpha-gal IgE antibodies (galactose-alpha-1,3-galactose IgE) . There is a high false-positive rate to this test (like other food allergy tests), which means it may come back showing someone may have alpha-gal syndrome when they actually don’t have it. Further, traditional tests to beef, pork, and rabbits with commercial extracts are often negative and will not be diagnostic. Again, it is important to know the history as an allergist must distinguish between true allergy to beef or pork as opposed to the person having AGS. Additionally, more in-depth testing may be needed to evaluate for something called pork-cat syndrome (another topic for another day). Other considerations include testing for specific IgE to porcine or bovine gelatin. There are a few centers in the United States equipped to utilize basophil activation testing as well. These are all reasons it may be beneficial to have the testing done by an allergist who has experience with knowing what tests to order for alpha-gal syndrome and how to interpret the results within the context of the person and their history. It is important to understand the nuance behind AGS and also other potential disorders the person may have.
How is AGS treated?
As with any food allergy, the treatment for alpha-gal syndrome involves avoiding the foods that cause a reaction. Ensure that the patient always has injectable epinephrine with them. The effectiveness of immunotherapy for AGS is currently being investigated. Preventing tick bites is the most important thing we can do to avoid AGS. Take proper precautions when outside and always check for ticks.
Here are some simple tips you can provide:
- Stay on trails and avoid walking through long grasses or bushes
- Wear long-sleeves and pants and treat the clothing with permethrin spray
- Use EPA-registered insect repellent
- Check your gear everyone including your pets for ticks when returning. Make sure there are eyes on the spots you can’t see.
- If you see a tick, remove it immediately and wash the area thoroughly.
Effects of global warming
As the climate is warming and the tick populations increasing, we must be more aware of this condition. This can go from something that was less common to an emerging health problem. It is important to also realize the uniqueness of the history and presentation so that patients can be referred and properly evaluated and treated.
References:
https://www.cdc.gov/ticks/alpha-gal/index.html
https://alphagalinformation.org/diagnosis-and-testing/
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