Researchers at the University of Tennessee Health Science Center in Memphis have found that the majority of known anaphylaxis cases reported to the allergy clinic are due to an allergy to alpha-gal (galactose-α-1,3-galactose). Alpha-gal is a complex sugar found in red meat such as beef, pork and lamb. A person may develop the allergy after they are bitten by a Lone Star tick. It is believed that increased awareness of the allergy plus availability of a blood test have led to the diagnosis of more alpha-gal allergies.
The researchers published their findings recently in the Annals of Allergy, Asthma and Immunology. They had previously reviewed cases at the clinic in 1993 and 2006 and did not find a reason for many unexplained cases of anaphylaxis. A blood test has recently become available that detects IgE antibodies to alpha-gal, which are produced as part of the allergic response. This meant that the researchers could now identify patients with antibodies to alpha-gal and explain the source of many of the anaphylaxis cases they reviewed for the most recent study.
"Of the 218 cases of anaphylaxis we reviewed [for the current study], 33 percent were from alpha-gal," says Debendra Pattanaik, MD, lead author of the study. "When we did the same review in 1993, and again in 2006, we had a great many cases where the cause of the anaphylaxis couldn't be identified. That number of unidentified cases dropped from 59 percent in 2006 to 35 percent in this report -- probably from the number of identified alpha gal cases."
Previous research has linked bites from the Lone Star tick to the sensitivity to alpha-gal and the resulting meat allergy, but researchers are not yet sure how the Lone Star tick bites lead to alpha-gal allergies. "We often think of ticks as carriers of infectious diseases, such as Lyme disease, but the research strongly suggests that bites from this particular species of tick can lead to this unusual allergy," said Melody C. Carter, M.D., staff clinician at National Institute of Allergy and Infectious Diseases (NIAID). "The association is increasingly clear, but we still need to discover exactly how these two events are linked and why some people with similar exposure to tick bites seem to be more prone to developing alpha-gal allergy than others."
Most cases of alpha-gal allergies have occurred in the Southeast region of the U.S. where the Lone Star tick is common, but the condition seems to be spreading north and west. The prevalence of the allergy is not yet known.
Another reason that researchers have found it difficult to link anaphylaxis cases to alpha-gal allergy is that reactions to foods typically occur rapidly, usually within minutes of eating the food, but symptoms of meat allergy can take 3 to 6 hours to occur. Signs and symptoms can include hives, itching, swelling of the lips, tongue, face and throat, shortness of breath, abdominal pain, diarrhea, nausea and vomiting. The significant delay between eating red meat and an allergic reaction can make it challenging to connect the culprit foods to symptoms.
"This unusually long-time gap between a meal and an allergic reaction is probably a big reason that alpha-gal allergies are often initially misdiagnosed," said Dean Metcalfe, M.D., chief of the Mast Cell Biology Section at NIAID, who has studied alpha-gal. "If you start to have trouble breathing in the middle of the night, you probably are not going to blame the hamburger you had for dinner."
There is no current treatment for alpha-gal allergy other than avoiding the foods that cause the reaction. Individuals who have severe reactions should carry a kit that contains an emergency injection of epinephrine.
Preventing the allergy means reducing the risk of tick bites by avoiding wooded and grassy areas, especially in spring and early summer, using a tick repellant that contains 20-30% DEET or permethrin and checking for ticks after spending time outside. "Alpha-gal allergy appears to be yet another reason to protect oneself from tick bites," said NIAID Director Anthony S. Fauci, M.D.