Weird Science: Tick Bites Can Cause Red Meat Allergy

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A bite from the bloodsucking arachnid shown above can turn a person into an unwitting vegetarian, and cases are on the rise.

Ticks, everyone’s favorite hematophagous ectoparasites (bloodsucking external parasites), have long been known to inflict all sorts of scourge upon humans. They carry around all kinds of pathogens in the form of bacteria, viruses, and protozoa. In fact, a single tick can carry more than one disease-causing agent, which can make diagnosis and treatment tricky after a bite.

The tiny vampires can give us Lyme disease, Colorado tick fever, Rocky Mountain spotted fever, tick-borne meningoencephalitis, and other diseases.tick

A few years ago, scientists discovered another curse the little troublemakers can inflict upon humans – they can induce an allergy to red meat.

The culprit is a species of tick known as the “Lone Star tick”, named for Texas – even though it doesn’t limit its residence to that state. In fact, it is very widespread in the US, as this CDC map shows.

Here’s how the tick induces the allergy:

The bugs harbor a sugar that humans don’t have, called alpha-gal. The sugar is also is found in red meat — beef, pork, venison, rabbit — and even some dairy products. It’s usually fine when people encounter it through food that gets digested.

But a tick bite triggers an immune system response, and in that high-alert state, the body perceives the sugar the tick transmitted to the victim’s bloodstream and skin as a foreign substance, and makes antibodies to it. That sets the stage for an allergic reaction the next time the person eats red meat and encounters the sugar. (source)

Cases are on the rise, and reactions in some people are so severe that they end up in the hospital. Possible symptoms include hives, swelling, anaphylaxis, vomiting, diarrhea, trouble breathing, and a drop in blood pressure. And the reaction isn’t always immediate – people with the allergy can go into a delayed anaphylactic shock four to six hours after eating red meat.

Dr. Scott Commins of the University of Virginia in Charlottesville said “I see two to three new cases every week.” Dr. Commins and a colleague, Dr. Thomas Platts-Mills, published the first paper linking the tick to the illness in 2011.

One of the first cases they saw was a bow hunter who had eaten meat all his life but landed in the emergency department several times with allergic reactions after eating meat. Cases in people who spent a lot of time outside kept popping up.

“It seemed something geographical. We thought at first it might be a squirrel parasite,” Commins said. “It took us a while to sort of put everything together” and finger the tick.”

Dr. Erin McGintee, an allergy specialist on eastern Long Island, an area with many ticks, has seen nearly 200 cases over the last three years. She told the AP that at least 30 involved children, and the youngest was 4 or 5. She is keeping a database to study the illness with other researchers.

“It is bizarre,” she said. “It goes against almost anything I’ve ever learned as an allergist,” because the symptoms can occur as long as eight hours after eating meat, rather than immediately, and the culprit is a sugar — a type of carbohydrate — whereas most food allergies are caused by proteins, she said.

Allergic reactions are treated with antihistamines to relieve itching. More severe cases are treated with epinephrine – and some sufferers carry shots just in case they are exposed again. Even though poultry hasn’t been linked with reactions, products like turkey sausage that contain meat byproducts can trigger the allergy.

As of now, doctors don’t know if the allergy is permanent. Some people show signs of declining antibodies over time, but many are hesitant to risk meat consumption again for fear of another reaction.

The meat allergy “does not seem to be lifelong, but the caveat is, additional tick bites bring it back,” Commins said.

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