What could make a person who has loved burgers and barbecue for decades suddenly give up red meat?
Look no further than the tiny Lone Star tick.
A bite from one of these ticks can cause an allergic reaction to a substance called alpha-gal (galactose-α-1,3-galactose), a sugar molecule found in just about all mammals except humans, says UNC Health allergist Scott Commins, MD, PhD.
When a Lone Star tick bites a nonhuman mammal, such as a deer or dog, it may then have alpha-gal retained in its saliva when it bites a person, kicking off the reaction.
“It’s not just a food allergy; it’s a syndrome,” Dr. Commins says. “These folks can react to medications, vaccines, heart valves (transplanted from pigs or cows) and other products where red meat is not the primary ingredient but can be included as a flavor enhancer. It can become a much bigger issue than giving up beef or barbecue.”
Some people also become allergic to dairy products, he says. Those who are extremely sensitive must beware of certain medicine capsules and candy containing gelatin, face creams containing collagen and lip balm containing lanolin, all of which contain alpha-gal sugar.
Outdoor-Loving Adults Are at Greatest Risk
Most people who have been diagnosed with alpha-gal syndrome are between ages 45 and 65. “It’s more common in adults than in children,” Dr. Commins says.
It affects both men and women, particularly those most likely to be bitten by ticks.
“Hunters, gardeners, hikers, farmers, game wardens and park rangers seem to be most at risk,” he says.
One important way alpha-gal syndrome is different from other food allergies: Someone with alpha-gal syndrome will experience symptoms four to six hours after consuming red meat or anything containing the alpha-gal sugar. In comparison, someone with an allergy to nuts will have an immediate reaction, such as hives or swelling.
Some people experience anaphylaxis, a potentially fatal reaction that can cause the body to go into shock. For this reason, Dr. Commins advises most people with alpha-gal syndrome to carry an epinephrine autoinjector.
Symptoms of Alpha-Gal Syndrome Can Be Different Each Time
Symptoms of alpha-gal syndrome include:
- Itchy rash or hives
- Nausea, vomiting or diarrhea
- Heartburn or indigestion
- Coughing, shortness of breath or difficulty breathing
- Drop in blood pressure
- Swelling of the lips, throat, tongue or eyelids
- Dizziness or feeling faint
- Severe stomach pain
The symptoms vary, not just from person to person but also in the same person, depending on what they have eaten and what they’re doing at the time.
“You can’t base your next reaction on the last one you’ve had,” Dr. Commins says. “Maybe you’re sick, or you’ve been exercising, or you had a couple of cold beers. Your symptoms will be different from the last time.”
Discovering Alpha-Gal Syndrome
Dr. Commins was part of the team that discovered the syndrome in 2008 during his allergy and immunology fellowship training at the University of Virginia. Because the symptoms were different from typical food allergies, many in the medical community were skeptical at first.
“My project at the time was to investigate a handful of people—six to 10—who were all telling us a similar story about a delayed allergic reaction after eating beef or pork or lamb,” he says. “We wanted to either prove or disprove that they had something in common. We had no idea that more than 34,000 people would be diagnosed with this syndrome over the next 10 years.”
Scientists are still trying to understand the role of the tick bite; alpha-gal syndrome is not caused by bacteria or viruses. It is not like Lyme disease or Rocky Mountain spotted fever, in which an infected tick transfers the bacteria directly to a human through a bite. The leading theory is that there is a reaction between animal blood containing the alpha-gal sugar and something in the saliva of some tick species, including Lone Star ticks, that activates the human immune response.
Alpha-Gal Syndrome Diagnosed Most in the South, East and Central U.S.
In the United States, most cases of alpha-gal syndrome have been reported in the southern, eastern and central regions. The most likely cause is a bite from the Lone Star tick, a common parasite that is difficult to distinguish from other ticks, except that females have a white spot on their backs. A bite from the Lone Star tick may cause a rash (called southern tick-associated rash illness, or STARI), but it does not carry Lyme disease.
While the Lone Star tick seems to be the cause of alpha-gal syndrome in the U.S., other ticks may be at fault in other parts of the world. Cases have been identified in Australia, Europe and South Africa, where Lone Star ticks are not found.
There is no known treatment for alpha-gal syndrome, Dr. Commins says, except to avoid red meat.
Alpha-Gal Syndrome Diet: If It Swims or Flies, You Can Eat It
Dr. Commins has a simple memory device for people wondering what meat they can eat if they have alpha-gal syndrome.
“I tell my patients to eat chicken, turkey or seafood,” he says. “If it swims or flies, it’s generally fine.”
Sometimes, the syndrome goes away on its own, he says, as long as the person is not bitten again by a Lone Star tick.
“The best thing to do is to take precautions to avoid tick bites,” he says. “Use DEET (bug spray). Wear clothes that have insecticides impregnated into them. It’s not fashionable, but it helps to tuck your pant legs into your socks. If you’re a runner, try to stick to the trail and not go into the tall grass.”
If you start having food allergy symptoms after eating red meat, talk to your doctor or find one near you. An antibody test will reveal whether you have alpha-gal syndrome.