Alpha-gal allergy

Alpha-gal allergy (or colloquially meat allergy) is a reaction to Galactose-alpha-1,3-galactose, whereby the body is overloaded with immunoglobulin E antibodies on contact with the carbohydrate. The alpha-gal molecule is found in all mammals apart from Old World monkeys and the apes (including humans).

Bites from the lone star tick or the chigger, which transfer this carbohydrate to the victim, have been implicated in the development of this delayed allergic response which is triggered by the consumption of mammalian meat products. Despite myths to the contrary, an alpha-gal allergy does not require the afflicted to become a vegetarian, as poultry and fish do not trigger a reaction.

The allergy most often occurs in the central and southern United States, which corresponds to the distribution of the lone star tick. In the Southern United States, where the tick is most prevalent, allergy rates are 32% higher than elsewhere. However, as doctors are not required to report the number of patients suffering the alpha-gal allergies, the true number of affected individuals is unknown.

Allergy

The allergy was first formally identified as originating from tick bites in a 2009 paper by Sheryl van Nunen. Prior to the paper's publication, Thomas Platts-Mills and Scott Commins, were attempting to discover why some patients were reacting negatively to the carbohydrate in the cancer drug Cetuximab. They had previously hypothesized that a fungal infection or parasite could lead to the allergy. It wasn't until Platts-Mills was bitten by a tick and developed alpha-gal allergies that his team also came to the conclusion that there was a link between tick bites and the allergy.

Alpha-gal allergies are very similar to Pork-Cat Syndrome and hence misidentification can occur.

Cause

Alpha-gal allergies develop after a person has been bitten by the Lone Star Tick in the United States, the European Castor Bean Tick, and the Paralysis Tick in Australia. Alpha-gal is not naturally present in apes and humans, but is in all other mammals. If a tick feeds on another mammal, the alpha-gal will remain in its alimentary tract. The tick will then inject the alpha-gal into a person's skin, which in turn will cause the immune system to release a flood of immunoglobulin E antibodies (a.k.a. IgE) to fight off the foreign carbohydrate. Researchers still do not know which specific component of tick saliva causes the reaction.

A 2012 preliminary study found unexpectedly high rates of alpha-gal allergies in the Western and North Central parts of the United States, which suggests that the allergy may be spread by unknown tick species. Examples of alpha-gal allergies were even present in Hawaii, where none of the ticks identified with the allergies live. Human factors were suggested but no specific examples were provided.

Symptoms

A typical allergic reaction to alpha gal has a delayed onset, occurring 3–8 hours after the consumption of mammalian meat products, instead of the typical rapid onset with most food allergies. After the delayed onset, the allergic response is typical of most food allergies, and especially an IgE mediated allergy, including severe whole-body itching, hives, angioedema, gastrointestinal upset, and possible anaphylaxis. These symptoms are caused by too many IgE antibodies attacking the allergen, in this case the alpha-gal. In 70% of cases the reaction is accompanied by respiratory distress and as such is particularly harmful to those with asthma.

Alpha-gal allergies are the first food allergies to come with the possibility of delayed anaphylaxis. It is also the first food-related allergy to be associated with a carbohydrate, rather than a protein.

Treatment and medical issues

Blood tests for IgE response indicating alpha gal allergy have not been approved by the U.S. Food and Drug Administration (FDA), and must usually be purchased by private individuals, but are available and are in use.

Alpha-gal is present in the anti-cancer drug Cetuximab, as well as the IV fluid replacements Gelofusine and Haemaccel. Blood thinners derived from porcine intestine and replacement heart valves derived from porcine tissue may also contain alpha-gal.

There has been at least one instance of a man with an alpha-gal allergy going into anaphylaxis after receiving a heart-valve. Some researchers have suggested that the alpha-gal which is prevalent in pig's tissue, and used for xenografts, may contribute to organ rejection.

Unlike most food allergies, the alpha-gal allergy can recede with time, as long as the person is not bitten by another tick. The recovery period can take anywhere from eight months to five years. This recovery potential is not confirmed, and some patients have had this allergy for several years. More research needs to be conducted to determine why some patients seem to recover and some do not.