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By Jared Weber, North Carolina Health News
On an average midsummer afternoon of 2017, Susan Davis noticed that a large tick had latched onto her waist. She had been walking her dog, Onyx, in the woods surrounding her Chapel Hill home earlier that day.
Davis, an audio journalism consultant, plucked the tick off quickly. Though a “very itchy red mark” remained where she had been bitten, she wasn’t worried. Growing up in the Midwest, she’d had plenty of experience with ticks.
A few weeks later, at a friend’s dinner party, Davis ate a meal she said she’s had countless times: a burger, salad and corn on the cob. That night, though, at about 1 a.m., she woke up in extreme discomfort.
“I was itching like crazy on my trunk, swelling around my face and covered in hives,” Davis said. “It was driving me sort of mad.”
A few Benadryl stifled the reaction and Davis went back to sleep.
The next day, she recounted the incident to one of her friends who works as a physician. The friend noted that it was a textbook allergic reaction. However, she was initially baffled as to specifically what kind.
“She asked me a million questions … and there was really [nothing] to indicate that it made sense,” Davis said. “And then, finally, she said to me: ‘Did you get any (insect) bites?’”
Remembering her recent tick bite, Davis showed her friend what remained of the rash.
“I bet you have that meat-allergy,” her friend said.
What is alpha-gal allergy?
In the past decade or so, Davis’s meat allergy has become somewhat of a conundrum for food allergy researchers.
Here’s what we know: those who develop the meat allergy suffer an allergic reaction after ingesting a complex sugar found in red meat called galactose-alpha-1,3-galactose or alpha-gal.
The sugar is found most commonly in mammals, but not in apes of African and Asian origin. This has led researchers to commonly refer to the condition as “mammalian-meat allergy.” Mammals are known for their red meat. Poultry, fish and other non-mammalian animals don’t apply here.
Since humans are primates of African descent, their bodies naturally contain no trace of alpha-gal.
The sugar can also be traced, in some occasions, to the saliva of lone-star ticks. The reddish-brown insects — and frequent disease vectors — are abundant in the Southeast U.S., where the majority of mammalian-meat allergy diagnoses have been made.
Charles Apperson, an entomologist and vector biologist at NC State University, said that humans do not tend to immediately feel lone-star tick bites on their bodies.
“A lot of times, you don’t know that you’ve been bitten by (lone-star ticks) until they’re fully attached,” Apperson said. “Then, you feel some sort of discomfort.”
But when the tick is able to fully sink its teeth into a human, sensitization — the initial allergen exposure that sets in motion the development of the full-on allergy — occurs.
“What we think happens is that the tick feeds on a lower mammal, such as a dog or a deer, and has alpha gal in its salivary glands,” said Scott Commins, a UNC-Chapel Hill allergist. “Then, it bites a human, and the remnant alpha-gal … seems to trigger an allergic-class immune response in some people.”
Researching mammalian-meat allergy and how it may develop in one’s immune system is Commins’ career work. Commins, who has worked at UNC-Chapel Hill since 2015, was part of the University of Virginia research team that first hypothesized the connection between alpha-gal and allergic reactions. This occurred while testing Cetuximab — a cancer treatment drug that also contains the sugar.
Commins estimates that many people have already been sensitized to the allergy, but he’s unsure what causes some people to have allergic reactions, and others to not.
The differences in reactions could be caused by human genetics, or it could be some other cause that’s yet unclear, Commins said. “Perhaps that difference is whether or not [the tick] had a recent blood meal.”
The responsibility lays with the ticks
A recent study at a Tennessee allergy clinic found that the state’s primary cause of anaphylaxis, a severe allergic reaction, is now mammalian-meat allergy.
Though no statewide studies have emerged yet, given North Carolina’s abundance of lone-star ticks, Apperson said that it’s no surprise the state has seen its fair share of cases.
In fact, Apperson said he recently completed a study with the Department of Epidemiology at the UNC Gillings School of Global Public Health, in which they asked foresters to collect ticks off their bodies and send them in for “identification and enumeration.”
In two years, scientists received close to 500 ticks; 93-94 percent of the vectors were lone-star ticks.
“That’s what people are encountering when they work in the woods or work outdoors,” Apperson said. “They’re lone-star ticks, and they’re attacking people.”
Carl Williams, public health veterinarian for the state Department of Health and Human Services, said that the state does not have any statistics on cases of mammalian-meat allergy. It’s not a communicable disease — meaning it can’t be passed from individual-to-individual — and thus is not reportable by state law.
But Commins estimates that, in certain areas of the state, 1-2 percent of the population might have already developed this allergy.
“In some of the rural counties, just so much of the population gets bites,” he said. “Sensitization can be in the 15-20 percent range” of those people.
Despite eliciting strong allergic reactions early on, the meat-allergy does not appear to be a chronic diagnosis. Those affected must avoid additional tick bites, though, if they wish to recover quickly.
Commins said that case length tends to vary on a patient-to-patient basis.
“We’ve seen it resolve as fast as around 18 months, and then, other times, we’ve seen it go away after more on the 3-4 years side,” he said.
A little over one year after realizing her condition, Davis has now become fully accustomed to avoiding red meat.
She misses Asian and Middle Eastern cuisine, as they both make extensive use of red meat. Davis travels a lot for her job, and not all places present as many white-meat or vegetarian options as the United States.
It’s not all been bad, though, she said. Davis said she lost some weight after initially being forced to monitor her diet.
“I think I’m healthier since I stopped eating meat,” Davis said.