HOUSTON– In central Virginia, where IgE-mediated delayed allergic reactions to red meat have become the most common cause of anaphylaxis in adults, physicians have taken to looking for what they call the ‘Mossy Oak sign.’
“If a patient shows up in a blaze-orange cap and hunter’s camouflage fatigues, an allergy fellow will tell me, ‘There’s a positive Mossy Oak sign in room 2,’ and I know that probably means the patient has delayed anaphylaxis to alpha-gal,” Dr. Scott P. Commins said at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.
Courtesy CDC
Alpha-gal is short for galactose-alpha-1,3,-galactose, an oligosaccharide present on thyroglobulin and other tissues in nonprimate mammals. It’s not normally present in humans, but when a lone star tick (Amblyomma americanum) that has fed on a nonprimate mammal bites a human, the alpha-gal is transferred, eliciting serum IgE antibodies.
Mossy Oak is a popular brand of hunter’s camouflage clothing. A positive Mossy Oak sign is useful in clinical practice because a patient who presents to a medical clinic dressed in hunting regalia is someone who spends a lot of time outdoors in the woods and fields where ticks lurk. He’s also typically someone who enjoys eating red meat. And whether it’s venison, beef, pork, lamb, goat, or bison, it contains alpha-gal. The result, in a patient who’s been primed via tick bite, can be a life-threatening anaphylactic or urticarial reaction arising 3-6 hours later, explained Dr. Commins, an allergist at the University of Virginia, Charlottesville.
He and his coinvestigators have played a central role in the still-unfolding story of this novel disease involving late-onset anaphylaxis to mammalian meat. Dr. Commins was the lead author of the paper that first described the syndrome (J. Allergy Clin. Immunol. 2009;123:426-33), as well as a subsequent paper that established the lone star tick as the culprit, making this syndrome the first known example of a response to an ectoparasite giving rise to a serious form of food allergy (J. Allergy Clin. Immunol. 2011;127:1286-93). More recently, the investigators have shown that alpha-gal-specific IgE does not cause or worsen asthma (Am. J. Respir. Crit. Care Med. 2012;185:723-30).
In a wide-ranging talk, Dr. Commins addressed the diagnosis and management of delayed anaphylaxis to red meat. He also touched upon some provocative emerging issues, including the possible risks posed by placing a porcine heart valve or bioprosthetic ligament in a patient with serum IgE antibodies to alpha-gal.
Bruce Jancin/Frontline Medical News
Dr. Scott P. Commins
The investigators stumbled upon the phenomenon of tick-transmitted delayed anaphylaxis to red meat while they were trying to unravel the explanation for the markedly regional occurrence of IgE-mediated hypersensitivity reactions to the chimeric monoclonal antibody cetuximab (Erbitux) previously reported in the oncology literature (J. Clin. Oncol. 2007;25:3644-8). Dr. Commins and his colleagues realized that the same southeastern and south-central states where reactions to the initial infusion of cetuximab were concentrated were the states where the lone star tick abounds.
Incidentally, scientists at the Centers for Disease Control and Prevention follow the lone star tick closely because it is the primary vector for ehrlichiosis. CDC researchers say the tick’s range is steadily expanding and now includes 28 states, with New York’s Long Island a hot spot.
There is no public health requirement to report serum IgE-mediated delayed reactions to red meat, so the exact number of affected patients is unknown. But it’s clear that many thousands of individuals are affected, and estimates are being revised upward as the novel syndrome becomes more widely known. The disorder is common in Europe and Australia as well.
Classically, IgE-mediated anaphylactic reactions occur within 5-30 minutes after exposure to the offending agent. Thus, the 3- to 6-hour delay in symptom onset in patients with a reaction to the alpha-gal in red meat is remarkable; the explanation for the time lag remains unclear.
Dr. Commins and others have shown that individuals with serum IgE antibodies to alpha-gal also typically have serum IgE antibodies to cat, dog, beef, and pork, but not to egg, peanut, chicken, fish, or house dust mite.
Diagnosis of IgE-mediated urticarial or anaphylactic reactions to mammalian meat is made on the basis of the presence of serum IgE antibodies to alpha-gal. Dr. Commins recommended considering the diagnosis and ordering the blood test in the setting of new-onset anaphylaxis in a patient who enjoys hunting or other outdoor activities in a state where the lone star tick is found, particularly if the symptoms occur at night, hours after a big meat-heavy meal. A history of recent or persistent tick bites is an obvious clue.