There are multiple tick species that are suspected to cause the development of this allergy, including Ixodes ricinus in Sweden and Ixodes holocyclus in Australia. Incidence of alpha-gal allergy has been reported in both of these countries in addition to the United States.4,5 Looking at histological slides, Hamsten, Starkhammar, Tran, Johansson, Bengtsson, Ahlén, Sällberg, Grönlund, and Hage4 saw antibodies against alpha-gal present in the gastrointestinal tract of I ricinus, providing evidence that tick bites might be associated with the development of IgE specific to alpha-gal. In the United States, the Amblyomma americanum is the tick species linked with alpha-gal allergy.2A americanum is also called the Lone Star tick because of the small white dot present on the scutum of females.6 The Lone Star tick inhabits the southeastern and south-central portion of the United States and is known to be present in almost all states where red meat allergies and IgE specific to alpha-gal has been seen. The geographic range of A americanum is increasing due to the rise of the deer population. As the number of deer continues to increase and populations continue to expand into areas that were once rural, the number of people exposed will continue to increase.3
The types of bites that are commonly known to precede development of IgE alpha-gal are bites that are extremely itchy and require a prolonged time to heal, multiple larval bites that can often be mistaken as chigger (larval mite) bites, repeated bites, and bites with a known long attachment.2,3 It is thought that once the affected person has been bitten by the tick, he or she then develops IgE that is specific to alpha-gal.3 When the sensitized person eats red meat such as beef, pork, lamb, or game, the alpha-gal-specific IgE binds to the antigen and causes an allergic cascade that involves the release of histamine from mast cells.2
Alpha-gal allergy is an unusual food allergy in many ways, which can make it trickier to diagnose. Most common food allergies are developed in childhood whereas in alpha-gal allergy, a majority of patients are diagnosed as adults.3,7,8 Typical reactions to most food allergies will occur immediately1,7; however, in alpha-gal allergy, the onset of symptoms is delayed and can begin any time between 3 to 7 hours after ingestion of red meat.9
Reported symptoms vary from mild reactions such as palmar and plantar pruritis9 to more severe reactions such as anaphylaxis with tongue swelling, throat constriction, and respiratory distress.5 Skin-prick testing to commercially prepared meat antigens are usually negative. Patients will usually react to skin-prick testing if fresh meat is used as the antigen.1,2,7,8,10 Before the discovery of alpha-gal allergy, many of these cases were thought to be either idiopathic or even psychological in nature.1 The unusual characteristics of this food allergy can make it difficult to diagnose.
The number of cases of alpha-gal sensitivity worldwide is increasing,10 and this increase in incidence makes it more likely that primary and urgent care providers will start to see this in their practice. There are reports of cases all throughout the Southern United States, with documented cases seen in Texas, Georgia, South Carolina, Mississippi, Kentucky, Oklahoma, West Virginia, Virginia, Tennessee, North Carolina, and Arkansas.2 Providers need to be aware of this new delayed onset allergy to red meat and consider it when patients present with pruritis, urticaria, and anaphylaxis with no other known cause.