An alpha-gal allergy is often discovered after eating red meat.
The term alpha-gal is short for galactose-alpha-1, 3-galactose, a carbohydrate molecule that can cause an allergic reaction in people with an alpha-gal allergy.
The molecule is found in the meat of mammals, including cows, sheep, venison, bison, and pigs.
Alpha-gal allergy is chiefly spread by the bite of the Lone Star tick, so named for the marking on its back.
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Causes of an alpha-gal allergy
Alpha-gal may enter the body via a Lone Star tick bite.
In the United States, the Lone Star tick is most common in Southeast Texas, Iowa, and New England. However, cases of the allergy have been noted in other parts of the country, including Hawaii, where the tick does not typically live.
The alpha-gal allergy was only identified in 2006 and doctors are still learning about the condition. Cases of alpha-gal allergy are becoming increasingly common but are still considered rare.
When alpha-gal enters the body, via a tick bite or otherwise, the immune system produces antibodies to fight the molecule.
Cetuximab contains the same alpha-gal sugar as meat, although the association was not made with tick bites until Platts-Mills himself was later bitten by ticks and developed the allergy.
It remains unclear exactly what substance in the tick's saliva causes the development of alpha-gal antibodies.
Most people discover they have an alpha-gal allergy after eating red meat. However, they can also have a reaction after eating foods that contain gelatin or taking medications that use gelatin as a stabilizer.
Common symptoms of an alpha-gal allergy include:
- stuffy or running nose
- feeling nauseated
- developing hives or a rash on the skin
- shortness of breath
An anaphylactic reaction restricts breathing and can be fatal, so it needs immediate medical treatment. Although rare, it has been known for people with an alpha-gal allergy to be admitted to the intensive care unit (ICU).
In some instances, it can take up to 4 to 6 hours after eating red meat before a reaction occurs. So, people with an alpha-gal allergy do not always associate the reaction with what they have eaten. Symptoms do not necessarily occur every time the person eats red meat.
The immune system of people with an alpha-gal allergy treats the alpha-gal molecule in meat as a physical threat to the body. Histamine and other chemicals are released to try to "protect" the person, and these cause an allergic reaction.
To determine if alpha-gal antibodies are present in the body, a blood test may be recommended by a doctor.
Many people who acquire an alpha-gal allergy have no history of other allergies or allergic symptoms.
However, discovering whether the person has had a tick bite in the preceding weeks or months will help a doctor make a diagnosis.
Often a doctor or allergist will ask:
- what and how much the person ate before the reaction
- how long it took for symptoms to develop
- what symptoms occurred and how long they lasted
Characteristics of red meat allergies differ from other allergies, as people do not usually experience symptoms until at least 2 hours after eating red meat. This delay can help doctors diagnose an alpha-gal allergy.
However, as the connection between the symptoms and the consumption of red meat is not always clear, often it takes an allergist with expert knowledge of the condition to diagnose it.
A blood test will identify whether alpha-gal antibodies are present in an individual's bloodstream. Results usually take 1 to 2 weeks.
A skin test can also be done, which involves a small amount of the food allergen pricked onto the skin.
If a wheal (a bump similar to a mosquito bite) develops, then it is a positive result. The test takes about 20 minutes and can be uncomfortable, but not usually painful.
Treatment and management
Once an allergy is diagnosed, the best treatment is for the person to avoid the trigger. In this case, all mammal meats should be avoided.
A person diagnosed with an alpha-gal allergy will probably have to change their diet and be careful when they eat out. Seafood, poultry, and eggs are acceptable protein choices for those with alpha-gal allergies. Many people can also tolerate dairy products.
How cautious a person needs to be will depend on how severe their symptoms are. For example, some people experience a reaction if their food was prepared in the same kitchen as red meat.
The first-line treatment for the serious reactions of anaphylaxis is epinephrine, which is available on prescription as an auto-injector. Epinephrine auto-injectors are sometimes called by the name of one brand of the device, EpiPen.
People diagnosed with an alpha-gal allergy will probably be prescribed an epinephrine auto-injector and be shown how to use it.
Anyone with the allergy should carry two doses of epinephrine with them at all times. They should use the auto-injector immediately if they have symptoms of an allergic reaction, including:
- shortness of breath
- repetitive coughing
- weak pulse
- tightness in the throat
- difficulty breathing or swallowing
Side effects of epinephrine can include:
Rare and more serious side effects of epinephrine include:
The best way to avoid contracting an alpha-gal allergy is to avoid getting bitten by ticks.
If people live in an area where Lone Star ticks are prevalent, there are ways to avoid getting bitten. These include:
- avoiding wooded, overgrown areas, or high grass where ticks live
- wearing light-colored clothing that fully covers the limbs when hiking or camping
- checking pets and livestock for ticks regularly
- using insect repellent
- washing clothing in hot water after returning from a wooded area
There is some evidence that a person may recover from alpha-gal allergy if they are not re-infected by another tick bite.