Mysterious link between beef and mutton allergies and tick bites

If you have been eating beef and mutton for 20 to 30 years without any problems, and suddenly one day you experience itching, redness, swelling, vomiting or even difficulty breathing after eating kebabs and stewed beef brisket, it is most likely not because of "recent immunity decline" or because the meat is not fresh - more than 90% of the time, it is because you have been bitten by a tick before and are suffering from "alpha-galactose syndrome", which is commonly known as "red meat allergy".

When I was rotating in the allergy department, I met a 42-year-old outdoor enthusiast named Lao Zhang. He goes hiking on Bashang three or four times a year. When he came back last summer, he had a red pimple on his waist. Although it was not painful or itchy, he didn't take it seriously. As a result, I went to eat roast leg of lamb with my friends half a month later. After chewing two small pieces of meat, I felt my throat tighten and a wheal suddenly appeared on my arm. When I was sent to the emergency room, my blood pressure dropped. At first, the doctor who treated me thought it was food poisoning. Then we sent him to our department to check common allergens, all of which were negative. Finally, we did an α-galactose IgE test. The indicator was more than 20 times higher than the normal value, and the cause of the disease was anchored to the tick half a month ago.

What many people don’t know is that α-galactose is found in almost all mammals except humans and great apes. When we usually eat beef and mutton, this molecule is almost completely broken down in the digestive tract, and the immune system cannot touch it at all, so most people will not be allergic to it for a lifetime. But ticks are different. This little thing lives by sucking the blood of mammals, and has a pile of α-galactose from cattle, sheep, and rabbits in its body. When it bites, it injects saliva mixed with α-galactose directly into your dermis or even your blood vessels. This is equivalent to passing the "foreign invader" directly under the nose of the immune system. It remembers the characteristics of this molecule on the spot and generates IgE antibodies specifically against it. Next time you eat beef and mutton, even if it is stewed to a pulp, as long as α-galactose that has not been completely destroyed by high temperature enters the blood, the antibodies will directly sound the alarm throughout the body, and an allergic reaction will come.

What’s interesting is that there’s a lot of debate in the academic community about the onset threshold of this disease. Epidemiologists believe that as long as you are bitten by an α-galactose-carrying tick, you will 100% produce corresponding antibodies. However, many people have low antibody levels, and their allergic reactions are as mild as just a little itchy skin, and they will not think about it at all. ； We who work in clinical practice do not agree with this conclusion. The department has counted 72 confirmed cases in the past three years, 61 of which have a history of allergic rhinitis or chronic urticaria. Their own immunity is prone to "over-excitation". On the contrary, people with completely normal immune function, even if they are bitten by the same type of tick, the amount of antibodies produced does not exceed the disease threshold, and obvious allergic reactions rarely occur. There are also studies saying that the longer the tick attaches to the human body and the more saliva is injected, the more severe the subsequent allergic reaction will be. We have indeed encountered patients who were bitten for three days before being discovered. In the end, they even developed a rash after eating pork, which just fits this rule.

Many people feel that they will never have a chance to eat red meat once they are diagnosed. In fact, it is not that exaggerated. I have a patient who strictly abstained from red meat for two years after the diagnosis. His antibodies were retested and have dropped below the normal level. Now he can eat medium-rare steak without any problem. There are also many people who are only allergic to half-cooked red meat. The α-galactose in fully cooked beef and mutton has been almost destroyed by high temperatures. It is completely fine to eat, and it is not necessary to cut it into pieces. Oh, yes, there are many people who have heard the rumors and dare not touch milk or eggs. In fact, it is completely unnecessary. The α-galactose content in milk is very low. More than 95% of patients can drink it normally. There is no need to add extra dietary restrictions to yourself.

To be honest, the misdiagnosis rate of this disease is really high now. Many people feel uncomfortable after eating red meat. Their first reaction is "the meat is not clean" and "the stomach has not been good recently". Some people even check whether it is gout or chronic urticaria. After a long detour, they think of checking for tick-related allergens. Especially now that more and more people like to hike and camp. After going to the grass or woods, you must carefully check whether there are any small dark brown bugs the size of rice grains on your body, especially in places with thin skin such as hair seams, armpits, and groin. Ticks secrete anesthetic substances when they bite, and they do not hurt at all. Many people do not even know they have been bitten. If you really find it bitten, don't squeeze it hard with your hands, don't use fire, grab its mouthparts with pointed tweezers and pull it out vertically. Just pull it out and disinfect it. If you feel uncomfortable after eating red meat within 1-2 months, go to the hospital to check for alpha-galactose antibodies. It costs a few dozen yuan and can save you a lot of detours.

Someone asked me before if there is any way to prevent it in advance? At present, there is really no targeted vaccine. All we can say is to take precautions when going outdoors, wear long clothes and long pants, and spray some mosquito repellent containing DEET. After all, being bitten by a tick is not only a red meat allergy, but also brucellosis and forest encephalitis. It never hurts to be more careful.