Immunologist Dr Andrew Baker reports on the discovery of a new allergy and the surprising way it is triggered, as well as its unusual features.
The story began in the United States. It was noticed that people in certain areas were having episodes of unexplained sudden rashes/itching/hives (also known as urticaria) and swelling (also known as angioedema).
Some patients had anaphylaxis or sudden abdominal pains and diarrhoea, and all these symptoms occurred between two to seven hours after eating red meat. So the attacks were not occurring in the first hour as normally happens with food allergy, but instead were quite delayed.
The next piece of the puzzle was that the attacks only occurred in certain areas of the United States. Some of the affected people reported being bitten by ticks, and it was noted that only the areas of the US that had the lone star tick were affected by this meat allergy. This led to the discovery of alpha-gal allergy.
What is alpha-gal allergy?
Alpha-gal allergy involves people experiencing delayed onset episodes of urticaria, angioedema, abdominal upset and even anaphylaxis following the consumption of red meat.
The strange thing is that a bite from a tick can set the process off. To start off alpha-gal allergy, first a tick bites a person. This can happen if the person has spent time outdoors, e.g., in long grass or with a pet that has been or is exposed to livestock. It is more likely to happen in summer but can be any time of the year.
The tick bites the person and injects its salivary protein into them. Unfortunately, bound together with that salivary protein can be a small amount of alpha-gal. Alpha-gal is a carbohydrate that ticks pick up from feeding on red meat animals, such as a cow, sheep or deer. As a result, the person is also injected with some alpha-gal.
The person’s immune system reacts to this alpha-gal and becomes allergic to it. Therefore, the next time the person eats red meat (which contains alpha-gal) they can have an allergic reaction – but with delayed symptoms as described above.
This only happens in relation to red meat, that is, meat from a mammal and not meat from chicken or fish.
The allergy is unusual because the symptoms are so delayed. As a result, attacks occur a long time after meat is eaten, often in the middle of the night. Further, reactivity can be intermittent and variable, so not occurring every time red meat is eaten. These factors make it hard to pin down a diagnosis.
It is also not only meat itself that has alpha-gal. Very high levels are in kidney and offal. Some people react to these only, but not meat. Very low levels can be in bovine gelatine; occasionally people react to this but most don’t.
Alpha-gal (meat) allergy in New Zealand and across the world
After being initially discovered in the US, alpha-gal allergy has now been found in other countries around the world, including Europe, Australia and Japan. There is a world map of alpha-gal allergy, with patients reported from many more countries.
New Zealand has alpha-gal allergy as well. The tick that causes it is predominantly in the upper half of the North Island but can be found elsewhere. It can be on livestock and deer, and living in the grass nearby, and can also get onto dogs. People are at more risk if they live in rural areas and/or get out into the outdoors more or have exposure to animals, including dogs.
It is unclear how rare it is, and only a handful of cases have been identified in New Zealand so far. The strange thing about alpha-gal allergy is it can be temporary and resolve spontaneously, although this is unpredictable.
Also reactions can be intermittent and occur at times very separate to when red meat is eaten, so for these reasons it might often not be identified. Sudden occasional anaphylaxis or rash events overnight could be consistent with alpha-gal allergy.
However, there are many other causes of rashes occurring overnight to consider, including some non-allergic ones. Nevertheless, it is something to consider in patients with random sudden allergy attacks and no other clear cause.
A referral to an immunologist/allergy specialist may be required as it is very much a niche diagnosis, which it would not be reasonable to expect a GP to necessarily know about.
The story of alpha-gal allergy has been unfolding around the world, so it will be interesting to see how this evolves in New Zealand.
Dr Andrew Baker (MBChB, FRACP) is an allergy/clinical immunology specialist at Waitemata Allergy Clinic.