A single bite from a tick can cause a permanent allergy to pork, beef and other kinds of red meat.
This condition is increasing in the United States, with a jump in positive test cases from 2017 to 2021, according to the U.S. Centers for Disease Control and Prevention (CDC). According to the CDC, as many as 450,000 people in the U.S. have been estimated to have been infected with alpha-gal syndrome, which can cause an assortment of symptoms when they eat red meat.
The connection between a tick bite and a meat allergy might seem baffling at first. How is it possible that a bite from such a small creature can ruin a lifetime of barbecues? Scientists suspect that it has to do with special sugar molecules found in lone star tick saliva, which humans don’t carry — but most other mammals do.
Where Are Lone Star Ticks Found?
The range of the lone star tick stretches from roughly the eastern half of Texas, up to Nebraska, then across southern Maine and back down to Florida, encompassing a huge portion of the lower 48 states. It’s also found in parts of Mexico, and occasionally reported in Canada.
Fittingly, the insect's name comes from a star-like white pattern on the back of adult females; typically, young females and males are predominantly maroon-colored.
These ticks are generalists, latching onto anything that passes by as they wait on the top of blades of grass or leaves. They are often found on deer and turkey, but in their younger stages they might even feed on rodents or smaller birds.
Like other insects, lone star ticks have three stages of development — larvae, nymphs and adults — and the organisms will readily feed on humans during all three of these phases, if if given the chance.
Read More: What You Need to Know About Lyme Disease
What Is Alpha-gal Syndrome?
People who have alpha-gal syndrome may experience a wide variety of issues when they eat red meat: Hives, a rash, nausea, vomiting, diarrhea, trouble breathing, dizziness, swelling, and stomach pain, among other afflictions.
Sometimes these symptoms appear right away; sometimes they only emerge after a delay of several hours. Not everyone feels all of them, though. Some patients only experience very mild symptoms, and not every bite will necessarily cause AGS. But others get it bad.
“Some people [with alpha-gal syndrome] are very sensitive even to the smell of meat,” says Yoonseong Park, an entomologist at Kansas State University who studies AGS and lone star ticks.
The syndrome also doesn’t affect people equally in different parts of North America. Park says that more AGS patients are found in certain states, like Missouri and Kentucky, than in other parts of the tick’s range. It’s unclear why so far, but research he is conducting shows that some ticks carry more of the molecules that cause the disease than others.
Park is currently collecting lone star ticks from around their range to find out how regions, climate or other factors may impact the rate of AGS transmission.
How Does Lone Star Tick Disease Work?
Lone star ticks can pick up a sugar molecule called alpha-gal when they feed on hosts that have it in their bodies naturally. Ticks inject a large number of alpha-gal molecules into their hosts when they feed, in order to turn off parts of the hosts’ immune system. These molecules will remain in their saliva, which the insects can pass into the bodies of new hosts while feeding. Alpha-gal is found in most mammals, but not humans, fish, reptiles, or birds.
For those affected by AGS, the presence of alpha-gal in human blood can trigger an individual's immune system to flood their bodies with immunoglobulin E (IgE) antibodies, including anti-gal, which is tailored specifically to alpha-gal molecules. Researchers believe that something else in the saliva makes our blood more sensitive to alpha-gal, though they aren’t yet certain what that might be.
“We believe that some components in the tick saliva, co-injected with the alpha-gal, turn on the immune systemic pathway sensitizing allergic reaction,” Park says.
At this point, the antibodies will reactivate every time people who are sensitive to this allergy consume meat that contains alpha-gal. Still, it doesn’t mean these individuals have to become vegetarian — usually, AGS patients can still consume chicken, fish and reptile meat. To avoid triggering symptoms, they just have to avoid pork, venison, beef, lamb, rabbit and other kinds of red meat.
How Can A Tick Bite Cause a Meat Allergy?
It isn’t certain why alpha-gal entering our bodies through tick bites triggers this response, especially when consuming red meat loaded with alpha-gal had little previous effect. But it likely has something to do with the presence of something else in tick saliva. Park is currently examining what happens when lone star ticks feed. His research on this isn’t yet published, but his team has also found that they release higher quantities of certain molecules when feeding on different hosts.
“Somehow, mysteriously, we find that when they feed on human blood, the alpha-gal level really goes up like crazy — 10 times higher than when feeding on other blood.”
The problem isn’t only limited to lone star ticks. While lone star ticks contain the highest quantities of alpha-gal in their saliva among species in North America, Park says that some black-legged ticks also contain smaller amounts of it.
Still, ticks in other parts of the world also can cause AGS, such as the Australian paralysis tick, the castor bean tick in Europe, and the Asian longhorned tick. The latter is now causing concern in the United States, where it has become an invasive species, spreading through nearly a dozen states.