In a previous post about ticks I described all the known diseases that ticks cause and what regions of the US are at risk. Now there is a new illness related to ticks, in particular the lone star tick, which lives mostly in the southeastern United States. It is called Alpha Gal syndrome (abbreviated AGS). It causes a severe allergy to red meat (meat from mammals). We are just beginning to learn about this, but in this post I will bring you up to date with what we know so far.
What is AGS
All mammals except for primates (which includes humans) have in their bodies a sugar molecule called galactose-⍺-1,3-galactose (abbreviated alpha gal). Because humans have no alpha gal, it is a foreign substance to humans but eating alpha gal in red meat usually does not cause an allergic response.
Some people develop IGE antibodies to alpha gal. When they eat meat that contains alpha gal (basically meat from any mammal) they can have a severe allergic reaction. This could involve rash, itching, trouble breathing, abdominal pain, diarrhea, vomiting or low blood pressure. A very severe allergic reaction (called anaphylaxis) can even be fatal. The allergic reaction can be immediate, or it can be delayed by several hours after eating red meat
What causes AGS
Evidence has begun to accumulate that the most common cause of AGS is tick bites. Certain tick species (in the US it is the lone star tick) have alpha gal in their saliva. No one really understands how it gets into the tick saliva. This is a very active area of research.
When a lone star tick bites a human, it injects some alpha gal into the blood stream. In some people, the immune system makes IGE antibodies to alpha gal. When that person eats red meat (which contains alpha gal) he/she develops AGS.
It takes a while for the IGE antibodies to form, so the reaction to red meat can develop hours to days to weeks after the tick bite or bites. At this point we don’t know if one tick bite can cause AGS or if it takes multiple tick bites. We also don’t know how long the tick needs to be attached to inject the alpha gal. For now, we have to assume that one tick bite could cause it until we accumulate more information.
How Common is AGS
Between 2010 and 2022 110,000 cases of AGS were reported to the CDC. Because many people, including physicians are unaware of AGS, the CDC estimates there may be as many as 450,000 people affected but who have not been tested. Here is a link to the CDC news release: Emerging Tick Bite-Associated Meat Allergy Potentially Affects Thousands.
How do you diagnose AGS
Your doctor sends your blood to one of the big commercial labs that can do a test for antibodies to alpha gal. If it is positive then you have AGS.
How do you treat AGS
The only treatment is to avoid red meat. Dairy products may contain alpha gal, so they should be avoided too. It is okay to eat chicken and fish, which do not contain alpha gal. It appears that in many people the allergy to alpha gal may diminish over about 3-5 years. At that point they may be able to eat red meat again.
AGS Prevention
The best prevention is to avoid getting a tick bite from a lone star tick.
Here is a picture of the female lone star tick (the female is the only one that bites).
Here is a map showing the distribution of lone star ticks.
Ticks tend to get on your clothes when you walk in high grass or brush. They do not fall out of trees on to you. They climb to the tip of a blade of grass or the twig of a bush and wait for some animal to brush by. When you plan to walk in an area where ticks might be it is a good idea to use a DEET insect repellent on your lower legs, feet arms and neck. Do a thorough body tick check after you have been in an area that might have ticks. You may need to enlist a spouse or partner in the tick check. If you find a tick attached, remove it immediately. You can use tweezers or a tissue and pull it straight out. The sooner you remove an attached tick the less likely it is that you will get AGS or any other tick borne infection. It is better, of course, to find ticks and remove them before they attach.
Ticks tend to move from your clothes to your body. Another way to prevent tick attachment is to put your clothes in a hot clothes dryer for 20 minutes after you have been in an area where you might have gotten ticks on your clothing. 20 minutes on high heat will kill any ticks on your clothing.
Bottom Line
AGS is an allergy to a sugar called alpha gal that is present in all mammals except primates. The lone star tick has alpha gal in its saliva and when it injects alpha gal into your blood stream it can cause your immune system to recognize alpha gal as a foreign substance. This causes an allergic reaction when you eat red meat. The allergic reaction can be mild or severe enough to cause anaphylaxis and even death. There is no treatment for AGS except to avoid red meat and dairy products. Tick bite prevention strategies are the best ways to avoid getting AGS.