Alpha-gal allergy

Alpha-gal allergy

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

Bites from certain ticks, such as the lone star tick in the US, which can 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.[2] 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. [3]

The allergy most often occurs in the central and southern United States, which corresponds to the distribution of the lone star tick.[4] In the Southern United States, where the tick is most prevalent, allergy rates are 32% higher than elsewhere.[5] 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.[6]

Signs and 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.[7] In 70% of cases the reaction is accompanied by respiratory distress and as such is particularly harmful to those with asthma.[8]

Alpha-gal allergies are the first food allergies to come with the possibility of delayed anaphylaxis.[8][9] It is also the first food-related allergy to be associated with a carbohydrate, rather than a protein.[9][10]

Cause

Amblyomma americanum, a vector for the allergy

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.[11][12] 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.[3] 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 IgE antibodies to fight off the foreign carbohydrate.[3][11] Researchers still do not know which specific component of tick saliva causes the reaction.[13]

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.[5] Examples of alpha-gal allergies were even present in Hawaii, where none of the ticks identified with the allergies live.[13] Human factors were suggested but no specific examples were provided.[5]

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.[11]

There has been at least one instance of a man with an alpha-gal allergy going into anaphylaxis after receiving a heart valve transplant.[11] Some researchers have suggested that the alpha-gal which is prevalent in pig's tissue and used for xenografts may contribute to organ rejection.[14]

Mechanism

Symptoms are caused by too many IgE antibodies attacking the allergen, in this case the alpha-gal.[11]

Diagnosis

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.[6]

Prognosis

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.[11][15][13] This recovery potential is not confirmed, and some people 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.

History

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 people were reacting negatively to the carbohydrate in the cancer drug cetuximab.[11][12] They had previously hypothesized that a fungal infection or parasite could lead to the allergy.[11][15] 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.[15] They found that the IgE antibody response to the mammalian oligosaccharide epitope, alpha-gal, was associated with both the immediate-onset anaphylaxis during first exposure to intravenous cetuximab and the delayed-onset anaphylaxis 3 to 6 hours after ingestion of mammalian food products, such as beef or pork.[16]

Alpha-gal allergies are very similar to Pork-Cat syndrome and hence misidentification can occur. Pork-cat syndrome usually elicits an immediate allergic response, while a true alpha-gal allergy typically features a delayed allergic reaction of 3 to 8 hours after ingestion of the allergen. [17]

References

  1. ↑ Commins, SP; Platts-Mills, TA (2013). "Delayed anaphylaxis to red meat in patients with IgE specific for galactose alpha-1,3-galactose (alpha-gal)". Curr Allergy Asthma Rep. 13 (1): 72–7. doi:10.1007/s11882-012-0315-y. PMC 3545071Freely accessible. PMID 23054628.
  2. ↑ "Alpha-Gal IgE Test - Galactose-alpha-1,3-galactose : Viracor-IBT Laboratories". Retrieved 9 January 2013.
  3. 1 2 3 Williams, Louise (December 27, 2013). "Just one bite". Sydney Morning Herald. Australia. p. 20.
  4. ↑ "Meat Allergy: Alpha-Gal Reaction From Lone-Star Ticks More Common In Central, Southern U.S. Regions". Retrieved 9 January 2013.
  5. 1 2 3 Chan, Amanda L. (November 9, 2012). "Where Meat Allergy From Ticks Is Most Common". Healthy Living.
  6. 1 2 Frazier, Andrea (March 20, 2014). "Tick bite makes Lusby woman allergic to meat". The Washington Post. pp. METRO; T20.
  7. ↑ "Viracor-IBT Laboratories Launches the First Assay to Identify a New Type of Delayed, IgE-based Allergic Reaction to Certain Meats" (Press release). Viracor-IBT Laboratories. September 13, 2010. Retrieved October 17, 2016.
  8. 1 2 Wolver, Susan E.; Sun, Diane R.; Commins, Scott P.; Schwartz, Lawrence B. (2013). "A peculiar cause of anaphylaxis: no more steak? The journey to discovery of a newly recognized allergy to galactose-alpha-1,3-galactose found in mammalian meat". Journal of General Internal Medicine. 28 (2): 322–5. doi:10.1007/s11606-012-2144-z. PMC 3614139Freely accessible. PMID 22815061. Lay summary – ScienceDaily (July 24, 2012).
  9. 1 2 Alvarez, Amanda (July 25, 2012). "Tick bite leads to curious meat allergy". Milwaukee Journal Sentinel. Retrieved March 24, 2014.
  10. ↑ Smith, Olivia (June 20, 2012). "Ticks causing mysterious meat allergy". CNN.
  11. 1 2 3 4 5 6 7 8 Zaraska, Marta (December 3, 2013). "Want hives with that burger?". The Washington Post. pp. HEALTH; E01.
  12. 1 2 Carta, Darla (September 5, 2013). "'Lone star' tick bites are tied to red meat, pork allergies". Retrieved March 24, 2014.
  13. 1 2 3 Kroen, Gretchen Cuda (November 16, 2012), Ticked Off About a Growing Allergy to Meat, ScienceNOW, retrieved March 24, 2014
  14. ↑ Travis, John (1995). "The xeno-solution: perils and promise of transplanting animal organs into people". Science News. 148 (19): 298–301. doi:10.2307/4018063. JSTOR 4018063. PMID 11653203.
  15. 1 2 3 Goetz, Gretchen (June 26, 2012). "Red Meat Allergy Likely Cause by Tick Bites". Food Safety News.
  16. ↑ Berg, Emily A.; Platts-Mills, Thomas A.E.; Commins, Scott P. (2014). "Drug allergens and food—the cetuximab and galactose-α-1,3-galactose story". Annals of Allergy, Asthma & Immunology. 112 (2): 97–101. doi:10.1016/j.anai.2013.11.014. PMC 3964477Freely accessible. PMID 24468247.
  17. ↑ Zaraska, Marta (December 3, 2013). "Cat owners can also develop meat allergy". The Washington Post. pp. HEALTH; E05.
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