How does a tick bite cause a red meat allergy?
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What is the main topic discussed in this episode?
Hey, it's Flora, and you're listening to Science Friday. For two decades, a perplexing illness has been spreading.
What is alpha‑gal syndrome and how did researchers first link it to Lone Star tick bites?
After a Lone Star tick bite, people find themselves having a severe allergic reaction to red meat. Gone are the days of burgers and steaks. Some people are sensitive even to the smell of barbecue or cow-derived gelatin. This tick-borne allergy is called alpha-gal syndrome. The CDC estimates up to 450,000 people in the U.S. may be affected, and that's up from just a few dozen documented cases in 2009. Dr. Scott Cummins started researching alpha-gal syndrome Almost 20 years ago, before anyone really knew what it was, he was part of the team that tied this allergy to ticks. He's an allergist and immunologist at the University of North Carolina's Medical School. Scott, welcome to Science Friday. Thanks for being here.
Thanks for having me.
I think people think of alpha-gal syndrome as a red meat allergy.
What are the typical symptoms of a red meat allergy caused by alpha‑gal?
That's the shorthand. But what are the symptoms?
Well, they're often the classic symptoms that bring people into an allergist's office. So itching, swelling, hives, and then frequently there's accompanying gastrointestinal distress.
So
terrible abdominal cramping and pain, often nausea, vomiting, diarrhea. You can even have progression from there where people will feel short of breath or have difficulty maintaining their blood pressure, the things that we think about as anaphylaxis.
What are people exactly becoming allergic to?
Well, they're allergic to a sugar. So alpha-gal is a carbohydrate, and the allergic antibody recognizes alpha-gal, which is present in the meat and tissues of all non-human mammals.
Okay, so this is a sugar that we must encounter all the time throughout our lives.
What exactly does the immune system react to — which molecule causes the allergy?
So what is in the Lone Star tick that is making people sensitive to the sugar?
Well, the ticks, it turns out, seem to have the sugar. And so when they bite a human, Their tick saliva and factors in the tick spit seem to cause the human immune system to create this allergic response. And in some ways, alpha-gal is just sort of an innocent bystander. And if it weren't in hot dogs, hamburgers, et cetera, we probably would never even know about this allergy. But the distribution of alpha-gal in the foods that we eat and the medications that we take create that issue.
I mean, can we get into the nerdy details here, though? Why is my body suddenly recognizing this sugar as bad when it comes from a tick, but not when it comes from a hot dog I've had the day before?
Yeah, that's a great question. And there's probably a nuanced answer, only some of which we really know about. But one portion of that is the route of administration. So oral, like you're eating your hot dog or hamburger, that seems to be associated with tolerance. So very unlikely to develop an allergic response just by consuming the food, particularly when it's been consumed for decades.
How does a tick bite trigger an allergic response to a sugar found in mammal meat?
The skin, however, is a fantastic way to make an allergic response. So it probably really matters that the tick bite is happening to our skin. And we don't really know the exact... factor and how it's hooked to alpha-gal, but probably the tick saliva contains what we might call alarmins. So it turns the human immune system on and activates it and basically is like a danger signal to our immune system. And then alpha-gal just becomes an innocent bystander that we make an allergic response to.
Is an alarmin a technical term?
It can be, but it's also a simple term.
You published a study recently that analyzed blood samples from people across 10 states. And you had this sort of amazing finding that one in four people had alpha-gal antibodies in their blood. What does this mean? Because not all those people have the syndrome, right?
Correct. Not at all. The numbers seem incredibly high, right? 20, 30% of blood donors in some states, but that's just what we call sensitization, meaning you have a positive blood test. overwhelmingly those people would eat red meat just fine. We have a major issue in the field of allergy and immunology with our blood tests and our skin tests for that matter too.
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Chapters
8 chapters
1
What is the main topic discussed in this episode?
0:03–0:11
2
What is alpha‑gal syndrome and how did researchers first link it to Lone Star tick bites?
0:11–1:08
3
What are the typical symptoms of a red meat allergy caused by alpha‑gal?
1:08–2:15
4
What exactly does the immune system react to — which molecule causes the allergy?
2:15–3:38
5
How does a tick bite trigger an allergic response to a sugar found in mammal meat?
3:38–5:49
6
Why do blood tests show many people with alpha‑gal antibodies but not all have symptoms?
5:49–8:41
7
Which ticks, life stages, and host factors increase the risk of developing alpha‑gal syndrome?
8:41–13:08
8
What treatments or prevention options exist now and what therapies are being explored?
13:08–17:45
Speakers
2 identifiedMore from Science Friday
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