Alpha-Gal Syndrome

Prologue: A Tale of Two Discoveries

Alpha-gal syndrome did not emerge from a single experiment or a single clinic. It took shape from two initially separate observations on opposite sides of the world — one involving severe reactions to a cancer drug, the other involving tick bites and delayed allergy to red meat. Only later were they recognised as different faces of the same syndrome.

I. The American Story: Cetuximab and an Unexpected Allergen

The clinical mystery

In the early 2000s, cetuximab (Erbitux), a chimeric mouse-human IgG1 monoclonal antibody against epidermal growth factor receptor, was adopted for colorectal cancer and squamous cell carcinoma of the head and neck. However clinicians in parts of the southeastern United States, particularly Tennessee, Arkansas, and North Carolina, reported seeing unusually high rates of immediate hypersensitivity reactions. The regional pattern was striking. Something had sensitised these patients before they ever received the drug. But what?

The 2008 NEJM breakthrough

Platts-Mills’ team at the University of Virginia showed that many patients who reacted to cetuximab already had pre-existing IgE antibodies before treatment. Among 76 cetuximab-treated patients, hypersensitivity reactions occurred in 25; IgE antibodies to cetuximab were detected in 17 of those 25, compared with only 1 of 51 non-reactors. The geographic signal was equally striking. IgE to cetuximab was found in 20.8% of control subjects in Tennessee, compared with 6.1% in northern California and just 0.6% in Boston. [Chung et al, 2008]

The implication was clear. This was not a random drug reaction. Something in the environment, and something more common in the southeastern United States, had already primed susceptible patients.

The unexpected culprit

The surprise was that the relevant IgE was not directed against a protein epitope, but against a carbohydrate… galactose-α-1,3-galactose, or alpha-gal. On cetuximab, this oligosaccharide was present on the Fab portion of the heavy chain as a result of production in a murine (mouse) cell line.

That finding mattered because humans, apes, and Old World monkeys lack the enzyme α-1,3-galactosyltransferase, and do not synthesise alpha-gal. Although naturally occurring IgM and IgG antibodies to alpha-gal were already recognised, the presence of specific IgE suggested a different kind of immune response. That implied prior sensitisation through some environmental exposure not yet understood.

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II. The Australian Story: Tick Bites and Red Meat Allergy

The observation: Sydney’s northern beaches, 2007

Simultaneously, and independently of the cetuximab work in the United States, Professor Sheryl van Nunen and colleagues at Royal North Shore Hospital in Sydney noted an unusual pattern in their allergy clinic. Patients from Sydney’s northern beaches were presenting with allergic reactions, often severe, after eating red meat. Many also reported prior tick bites in an area endemic for Ixodes holocyclus, the Australian paralysis tick.

The 2007 ASCIA abstract

This abstract is the first formal report linking tick bite reactions with mammalian meat allergy in humans. It described 25 adults from Sydney’s northern beaches, of whom 23 had experienced allergic reactions to red meat, 14 had suffered severe anaphylaxis, and 24 reported tick bites before the onset of their meat allergy.

The importance of the report was clinical rather than mechanistic. Van Nunen and colleagues had identified a reproducible syndrome: tick bites first, red meat reactions later.

The 2009 MJA paper

The subsequent Medical Journal of Australia paper expanded the case series. Of the 25 patients with red meat allergy, 24 reported significant local tick bite reactions, painful, pruritic lesions greater than 50 mm that persisted for at least a week, before the onset of their meat allergy. Seventeen had experienced severe reactions to tick bites themselves, including tongue swelling, throat tightness, or shortness of breath. All 25 patients lived in a region endemic for Ixodes holocyclus.

A retrospective control group of 29 patients from the same area with non-meat food allergy had also been exposed to ticks, but none had developed mammalian meat allergy. The comparison suggested that tick exposure alone was not sufficient, and that the nature of the tick bite response might matter.

At the time, the mechanism remained uncertain. The authors discussed possible cross-reactivity between tick-derived and meat-derived antigens, but the alpha-gal explanation had not yet been established. What the Australian work had provided was the first clear clinical description of the syndrome that the American studies would soon help explain.

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III. Connecting the Dots

The Commins–Platts-Mills synthesis

The crucial synthesis came in 2009, when Scott Commins, then a doctoral researcher with Platts-Mills at the University of Virginia, showed that patients with delayed allergic reactions after eating red meat had IgE antibodies specific for alpha-gal.

The publication clarified several features that are now recognised as characteristic of alpha-gal syndrome: a delay of approximately 3–6 hours between ingestion and symptoms, weak or negative standard skin prick testing to meat extracts, and a history of prior tick bites in most patients. It also cited van Nunen’s Australian observations, helping connect the emerging American and Australian stories into a single syndrome.

Rather than discovering a new food allergy in isolation, this paper linked the two previously puzzling observations of unexplained cetuximab reactions and delayed allergy to mammalian meat.

Strengthening the tick link

The 2011 follow-up paper provided strong evidence that tick bites were central to sensitisation in the United States, particularly bites from the lone star tick (Amblyomma americanum). The study documented rises in alpha-gal–specific IgE after tick bites and found that the magnitude of the response correlated with the reported number of bites. This moved the field beyond association alone and made tick exposure the leading explanation for alpha-gal sensitisation in the United States.

A scientist becomes his own patient

In August 2007, Platts-Mills himself developed alpha-gal syndrome after exposure to lone star tick larvae whilst hiking in Virginia. In November of that year he first experienced delayed urticaria after eating lamb while travelling in London.

I eat lamb and five hours later, I’m covered in hives. What has taken five hours to get there? The only logical explanation is fat particles…that’s where our research is going.

Platts-Mills 2019

Platts-Mills own experience of a delayed reaction helped reinforce an idea that would become central to understanding the condition. As he later put it, “Ticks, red meat, allergy and a delay.”

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IV. The Evolutionary and Immunological Context

Why alpha-gal exists, and why we react to it

Alpha-gal (galactose-α-1,3-galactose) is an oligosaccharide found on glycolipids and glycoproteins in most non-primate mammals, including cows, pigs, sheep, and goats. During primate evolution, humans, apes, and Old World monkeys lost the enzyme α-1,3-galactosyltransferase and therefore do not synthesise alpha-gal themselves.

As a result, humans commonly carry naturally occurring antibodies to alpha-gal, particularly IgM and IgG, thought to arise in part from exposure to gut microbes bearing structurally similar epitopes. What is unusual in alpha-gal syndrome is not recognition of the molecule itself, but the development of an IgE response.

How the tick may do it

Tick bites appear to provide the missing sensitising event. As a tick feeds, it breaches the skin and introduces saliva containing a complex mixture of bioactive molecules, including anticoagulants, immunomodulators, and other salivary proteins. In some tick species, alpha-gal or alpha-gal–bearing material has also been identified in salivary tissues, supporting the idea that the bite can expose the host to the relevant epitope in a highly immunologically active setting.

The leading hypothesis is that this combination of skin injury, salivary immune modulation, and alpha-gal exposure promotes a Th2-skewed response and IgE class switching in susceptible individuals. Alarmins such as IL-33, TSLP, and IL-25 are plausible participants in this process, although the precise pathway remains incompletely defined.

Evidence from the United States suggests that the lone star tick, Amblyomma americanum, plays a central role in sensitisation there. Experimental work supports the view that alpha-gal in salivary tissue is not simply passively acquired from a previous host, and may in part be generated by the tick itself. Even so, not every tick bite leads to clinically relevant sensitisation, and the determinants of individual susceptibility remain uncertain.

An important distinction is that sensitisation is not the same as disease. Detectable alpha-gal–specific IgE indicates sensitisation, but clinical reactivity depends on subsequent exposure to alpha-gal–containing foods, drugs, or medical products. This helps explain why some patients remain asymptomatic, while others develop delayed urticaria, angioedema, anaphylaxis, or predominantly gastrointestinal symptoms.

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V. The Peculiar Phenotype

The delay, and what may cause it

Alpha-gal syndrome behaves differently from most IgE-mediated food allergy. Whereas standard food allergic reactions usually occur within minutes, alpha-gal reactions typically begin 3–6 hours after ingestion and may be delayed up to 8 hours. Clinically, that delay matters. It contributes both to the delayed diagnosis and to patients failing to connect an evening meal with nocturnal urticaria, abdominal pain, or anaphylaxis.

Allergy	Typical Onset	Comment
Peanut allergy	~median 3 minutes
Most IgE-mediated food allergy	90%within 30 minutes	<2 hours (98%)
Alpha-gal syndrome	3–6 hours	Can be to 8 hours

The leading explanation for this delayed onset is lipid absorption kinetics. Alpha-gal appears to be carried predominantly on glycolipids rather than on rapidly absorbed soluble proteins. After ingestion, lipid-bound alpha-gal is packaged into chylomicrons, enters the lymphatics, and reaches the systemic circulation only hours later. This model may help explain several characteristic features of the syndrome: delayed onset, variability from one exposure to the next, and the tendency for higher-fat mammalian foods and dairy products to provoke more severe reactions in some patients. Cofactors such as fatty meals, alcohol, and exercise may further lower the reaction threshold.

An additional clinical wrinkle is that reactions do not always present in the standard way. Some patients develop urticaria or angioedema, others frank anaphylaxis, and some present predominantly with gastrointestinal symptoms. As the 2025 fatal case report makes clear, severe isolated abdominal pain several hours after mammalian meat ingestion may represent anaphylaxis rather than a primary gastrointestinal disorder.

The skin-test paradox

Early investigators were also struck by how poorly standard skin prick testing matched the clinical syndrome. Skin prick testing with mammalian meat extracts was often weakly positive or near-negative, whereas delayed responses after intradermal testing more closely mirrored the clinical pattern. This mismatch helped establish alpha-gal syndrome as an unusual form of IgE-mediated allergy and reinforced the importance of serum alpha-gal–specific IgE testing over routine skin testing in suspected cases.

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VI. Beyond Allergy: a Possible Link to Atherosclerosis

Interest in alpha-gal syndrome has extended beyond allergy after observational studies raised the possibility that sensitisation to alpha-gal may be associated with coronary atherosclerosis.

In 2018, Wilson and colleagues reported that alpha-gal–specific IgE was associated with greater atheroma burden and plaque features considered higher risk. This finding was intriguing, but preliminary.

A later prospective study of patients undergoing coronary angiography also found that alpha-gal sensitisation was associated with increased non-calcified plaque burden, obstructive coronary artery disease, and STEMI, independent of measured traditional cardiovascular risk factors.

The proposed mechanism is biologically plausible. Repeated exposure to mammalian-derived products in sensitised individuals may promote low-grade vascular inflammation through IgE- and mast cell–mediated pathways. However, this remains a hypothesis rather than an established causal model.

For now, these findings are best viewed as a signal deserving further study, not proof that alpha-gal sensitisation directly causes atherosclerosis or that stricter dietary avoidance reduces cardiovascular risk. In current practice, avoidance advice should primarily be directed at preventing allergic reactions; any broader cardiovascular benefit remains unproven.

Platts-Mills and colleagues have speculated that strict avoidance may reduce cardiovascular risk, not just allergic symptoms. However whether alpha-gal is merely a marker of risk or an active participant in vascular disease remains uncertain. For now, the cardiovascular story is provocative — but not yet practice-changing.

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VII. Management

Diagnosis

Diagnosis requires clinical suspicion. The key features are

• a delayed reaction, usually 3–8 hours after ingestion of mammalian meat or related products;
• nocturnal reaction pattern: eating meat for dinner and waking overnight with urticaria, abdominal pain, or anaphylaxis;
• variable reactivity from one exposure to the next. Co-factors (fat load, alcohol, exercise) influence threshold
• a history of tick bites in an endemic area.
• Serum alpha-gal–specific IgE is the key diagnostic test. Elevated level ≥0.1 kU/L is positive, and ≥1% of total IgE is clinically relevant

Standard skin prick testing with meat extracts is often weakly positive or negative and intradermal testing shows delayed peak reactivity at 4–6 hours. So serum specific IgE is usually more useful than routine skin testing.

Avoidance and hidden exposures

Once alpha-gal syndrome is diagnosed, counselling should focus on avoidance of mammalian meat broadly and awareness of less obvious exposures. ASCIA guidance specifically includes kangaroo among mammalian meats relevant to mammalian meat allergy, so it is safer to avoid “safe species” language and instead frame advice around avoidance of mammalian products as a group. Some patients also react to dairy products, gelatin, medications, or medical products containing mammalian-derived material.

Category	Examples	Practical note
Mammalian meat	Beef, pork, lamb, goat, venison, rabbit, kangaroo and other mammalian meats	Counsel avoidance broadly rather than relying on species-specific exceptions
Dairy products	Milk, cream, butter, cheese, yoghurt, ice cream	Higher-fat dairy may be more problematic in some patients
Gelatin	Gummies, marshmallows, jelly, confectionery	Important hidden source
Medications	Gelatin capsules, heparin, pancreatic enzymes	Check formulation with pharmacist when relevant
Medical products	Bioprosthetic valves, gelatin colloids such as Gelofusine or Haemaccel	Important peri-operative and emergency consideration

Emergency preparedness

Patients with confirmed alpha-gal syndrome and clinical reactivity should have an adrenaline device, a written ASCIA Action Plan for Anaphylaxis, and training for patients and household contacts in recognising and treating anaphylaxis. Medical identification is also sensible, particularly for patients at risk of exposure to hidden mammalian-derived products in emergency or peri-operative settings. ASCIA recommends adrenaline as first-line treatment for anaphylaxis and emphasises training in the prescribed device.

Tick bite prevention

Preventing further tick bites is central, because re-sensitisation can occur after new exposures. In tick-endemic areas, practical measures include insect repellents, permethrin-treated clothing, avoiding long grass and leaf litter, and careful skin inspection after outdoor activity.

Tick removal: Australia “Freeze it, don’t squeeze it”

Australian guidance emphasises freezing the tick rather than squeezing or forcibly removing it. ASCIA advises using a product that rapidly freezes and kills the tick, allowing it to drop off naturally. Do not forcibly remove the tick, and do not disturb it with inappropriate chemicals. If the tick does not drop off, or cannot be frozen, medical help should be sought. In patients with prior tick allergy or tick-triggered anaphylaxis, tick removal should be treated cautiously and adrenaline should be readily available.

Vaccines and other medical products

Clinicians should be alert to gelatin-containing or mammalian-derived medical products. Rather than hard-coding a short list, it is safer to direct readers to the current Australian Immunisation Handbook components table, because product formulations and availability change. As of the current Handbook, gelatin is present in some vaccine products used in Australia, including certain MMR/varicella formulations and some rabies and oral typhoid products. The practical message is to check current product components and seek specialist review when there is concern.

Other relevant medical exposures include gelatin colloids, porcine-derived heparins, pancreatic enzyme preparations, bioprosthetic valves, some haemostatic agents, and selected bovine collagen products. These do not affect every patient in the same way, but they should be recognised as potentially important exposures. ASCIA’s patient guidance also notes that gelatin colloids such as Haemaccel and Gelofusine are relevant examples, although they are no longer commonly used in Australian resuscitation practice.

Follow-up and natural history

Alpha-gal IgE levels may decline over time if further tick bites are avoided, and some patients lose clinical reactivity after several years. Resolution is not universal, however, and renewed tick exposure may re-sensitise patients. Follow-up is therefore useful both to reassess risk and to reinforce tick-bite prevention. The possible cardiovascular implications of ongoing asymptomatic exposure remain uncertain, so avoidance advice should primarily be framed around prevention of allergic reactions.

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Part VIII: A Fatal Case Report Published in 2025

In 2025, Platts-Mills and colleagues published a well-documented fatal case of delayed anaphylaxis associated with alpha-gal sensitisation.

The patient, a previously healthy 47-year-old man from New Jersey, had an earlier probable warning episode in the summer of 2024. On a camping trip, he ate beef steak at 10:00 PM (unusual as he typically ate chicken), and awoke at 2:00 AM with severe abdominal discomfort, diarrhoea and vomiting. After about two hours the symptoms settled, and by morning he felt well enough to walk five miles. Neither he nor his wife recognised the event as anaphylaxis; as the paper puts it, they did not connect the pain with the beef eaten four hours earlier. Two weeks later, after eating a hamburger at a barbecue, he collapsed approximately four hours later and died despite prolonged resuscitation.

Post-mortem testing provided the missing diagnosis. The initial autopsy was reported as “sudden unexplained death,” but subsequent blood analysis showed:

• serum tryptase >2,000 ng/mL: one of the highest levels recorded in fatal anaphylaxis (the highest surviving value Platts-Mills had seen in practice was 100 ng/mL)
• positive alpha-gal-specific IgE (0.57 IU/mL): confirmed sensitisation
• positive IgE (sensitisation) to beef, ragweed and alpha-gal

The history also suggested a likely sensitising event. On further questioning, his wife described 12 or 13 “chigger” bites around his ankles earlier that summer. The authors note that in the eastern United States, bites labelled by patients as “chiggers” are often actually lone star tick larvae, an important cause of sensitisation to alpha-gal.

The case is important for several reasons. First, it demonstrates that the characteristic delay in alpha-gal reactions does not imply benign disease. Second, the early presentation may be misleading: in this report, severe abdominal pain preceded collapse, reminding clinicians that anaphylaxis may present without the immediate rash-and-wheeze pattern seen in other food allergies. Third, the history suggested prior exposure to presumed “chigger bites,” which the authors noted may in some cases represent bites from lone star tick larvae.

The authors proposed several possible contributors to severity, including alcohol, exercise, pollen exposure, and infrequent red-meat intake, but these should be viewed as hypotheses rather than established causal cofactors from a single case.

The main clinical message is simpler. Alpha-gal syndrome can be fatal, delayed reactions can be diagnostically deceptive, and unexplained collapse or severe abdominal symptoms several hours after mammalian meat ingestion should raise suspicion

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Part IX: Unanswered Questions

Despite two decades of research, important questions remain:

• Why do some tick bites induce sensitisation while others do not, and what determines individual susceptibility?
• Which components of tick saliva are most important in promoting Th2 skewing and IgE class switching?
• Why does the syndrome remit in some patients yet persist for years or decades in others?
• Does strict avoidance of mammalian products alter cardiovascular risk, or is alpha-gal sensitisation simply a marker of risk rather than a cause?
• How many cases of delayed anaphylaxis, unexplained gastrointestinal episodes, or sudden unexplained death may in fact represent unrecognised alpha-gal syndrome?
• Why do some patients present predominantly with gastrointestinal symptoms, often leading to prolonged diagnostic delay?
• As implicated tick species expand into new regions, what will the epidemiological impact be?

Alpha-gal syndrome is a reminder that medicine still has room for surprises: a carbohydrate rather than a protein, a food allergy measured in hours rather than minutes, and a syndrome recognised only when clinicians in different settings noticed that the usual explanations no longer fit. A sugar. A tick. A delayed reaction in the night. And a disease still teaching us how much we do not yet understand.

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References

Original Discovery — The Australian Story

• Van Nunen SA, Fernando SL, Clarke LR, Boyle RX. The association between Ixodes holocyclus tick bite reactions and red meat allergy [abstract]. Internal Medicine Journal 2007; 37 (Suppl. 5): A132. Presented at the 18th Annual Scientific Meeting of the Australasian Society of Clinical Immunology and Allergy (ASCIA), Fremantle, Western Australia, November 2007 
• Van Nunen SA, O’Connor KS, Clarke LR, Boyle RX, Fernando SL. An association between tick bite reactions and red meat allergy in humans. Med J Aust. 2009 May 4;190(9):510-1.

Original Discovery — The American Story

• Chung CH, Mirakhur B, Chan E, Le QT, Berlin J, Morse M, Murphy BA, Satinover SM, Hosen J, Mauro D, Slebos RJ, Zhou Q, Gold D, Hatley T, Hicklin DJ, Platts-Mills TA. Cetuximab-induced anaphylaxis and IgE specific for galactose-alpha-1,3-galactose. N Engl J Med. 2008 Mar 13;358(11):1109-17.

Clinical description

• Commins SP, Satinover SM, Hosen J, Mozena J, Borish L, Lewis BD, Woodfolk JA, Platts-Mills TA. Delayed anaphylaxis, angioedema, or urticaria after consumption of red meat in patients with IgE antibodies specific for galactose-alpha-1,3-galactose. J Allergy Clin Immunol. 2009 Feb;123(2):426-33. 

Tick vector confirmation

• Commins SP, James HR, Kelly LA, Pochan SL, Workman LJ, Perzanowski MS, Kocan KM, Fahy JV, Nganga LW, Ronmark E, Cooper PJ, Platts-Mills TA. The relevance of tick bites to the production of IgE antibodies to the mammalian oligosaccharide galactose-α-1,3-galactose. J Allergy Clin Immunol. 2011 May;127(5):1286-93.e6.
• Hester WP. Meet the Doc Who Discovered the Infamous Red Meat Allergy Spread by Ticks. UVA Today 2019

Cardiovascular Links

• Wilson JM, Nguyen AT, Schuyler AJ, Commins SP, Taylor AM, Platts-Mills TAE, McNamara CA. IgE to the Mammalian Oligosaccharide Galactose-α-1,3-Galactose Is Associated With Increased Atheroma Volume and Plaques With Unstable Characteristics-Brief Report. Arterioscler Thromb Vasc Biol. 2018 Jul;38(7):1665-1669
• Vernon ST et al. Immunoglobulin E Sensitization to Mammalian Oligosaccharide Galactose-α-1,3 (α-Gal) Is Associated With Noncalcified Plaque, Obstructive Coronary Artery Disease, and ST-Segment-Elevated Myocardial Infarction. Arterioscler Thromb Vasc Biol. 2022 Mar;42(3):352-361.

Fatal Case Report

• Platts-Mills TAE, Workman LJ, Richards NE, Wilson JM, McFeely EM. Implications of a fatal anaphylactic reaction occurring 4 hours after eating beef in a young man with IgE antibodies to galactose-α-1,3-galactose. J Allergy Clin Immunol Pract. 2025 Dec;13(12):3422-3424. 

Comprehensive Reviews — Australian Focus

• van Nunen S. Tick-induced allergies: mammalian meat allergy, tick anaphylaxis and their significance. Asia Pac Allergy. 2015 Jan;5(1):3-16. 
• van Nunen SA. Tick-induced allergies: mammalian meat allergy and tick anaphylaxis. Med J Aust. 2018 Apr 16;208(7):316-321.

Comprehensive Reviews — International

• Platts-Mills TAE, Li RC, Keshavarz B, Smith AR, Wilson JM. Diagnosis and Management of Patients with the α-Gal Syndrome. J Allergy Clin Immunol Pract. 2020 Jan;8(1):15-23.e1. 
• Commins SP. Diagnosis & management of alpha-gal syndrome: lessons from 2,500 patients. Expert Rev Clin Immunol. 2020 Jul;16(7):667-677. 
• Platts-Mills TAE, Commins SP, Biedermann T, van Hage M, Levin M, Beck LA, Diuk-Wasser M, Jappe U, Apostolovic D, Minnicozzi M, Plaut M, Wilson JM. On the cause and consequences of IgE to galactose-α-1,3-galactose: A report from the National Institute of Allergy and Infectious Diseases Workshop on Understanding IgE-Mediated Mammalian Meat Allergy. J Allergy Clin Immunol. 2020 Apr;145(4):1061-1071
• Peterson CJ, Mohankumar P, Tarbox JA, Nugent K. Alpha-Gal Syndrome: A Review for the General Internist. Am J Med Sci. 2025 Mar;369(3):313-320.
• Propst SBH, Thompson DK. Alpha-gal syndrome and the gastrointestinal reaction: a narrative review. Front Allergy. 2025 Jan 24;6:1535103.

Epidemiology

• Thompson JM, Carpenter A, Kersh GJ, Wachs T, Commins SP, Salzer JS. Geographic Distribution of Suspected Alpha-gal Syndrome Cases – United States, January 2017-December 2022. MMWR Morb Mortal Wkly Rep. 2023 Jul 28;72(30):815-820.
• Carpenter A, Drexler NA, McCormick DW, Thompson JM, Kersh G, Commins SP, Salzer JS. Health Care Provider Knowledge Regarding Alpha-gal Syndrome – United States, March-May 2022. MMWR Morb Mortal Wkly Rep. 2023 Jul 28;72(30):809-814.

Gelatin Allergy and Cross-Reactivity

• Mullins RJ, James H, Platts-Mills TA, Commins S. Relationship between red meat allergy and sensitization to gelatin and galactose-α-1,3-galactose. J Allergy Clin Immunol. 2012 May;129(5):1334-1342.e1.

Alpha-Gal and Novel Australian Tick Species

• Kwak M, Somerville C, van Nunen S. A novel Australian tick Ixodes (Endopalpiger) australiensis inducing mammalian meat allergy after tick bite. Asia Pac Allergy. 2018 Jul 26;8(3):e31.