Highlight on Tennessee: Red Meat Allergies Linked to Tick Bites on the Rise

Clinics associated with Vanderbilt University’s Asthma, Sinus, and Allergy Program (ASAP) are diagnosing at least one alpha-gal allergy per week in the Nashville area, according to Robert Valet, MD. The allergy is triggered by consuming galactose-alpha-1,3-galactose (alpha-gal), a type of sugar that is present in red meat. Researchers believe that the primary cause of the allergy is a bite from the lone star tick, a common Tennessee pest.

Cetuximab Allergic Reaction

In 2002, researchers at the University of Virginia (UVA) began investigating allergic reactions to cetuximab, a cancer drug used to treat metastasized colorectal cancer and squamous cell carcinoma of the head and neck. The allergic reactions, which included anaphylaxis, were much more common in patients who live in Southeastern states, particularly Tennessee and North Carolina.  Dr. Thomas Platts-Mills, chief medical professor of Asthma, Allergy and Immunology at UVA, led the research team investigating the cause of the geographic discrepancy: 22 percent of patients in Tennessee experienced allergic reactions to cetuximab, while less than 1 percent of Massachusetts reacted similarly. In 2008, the team published its findings. Patients with hypersensitivity to cetuximab had certain IgE antibodies in their blood prior to treatment; the antibodies attacked alpha-gal, which is found in cetuximab. These antibodies were present in far more patients in the Southeast than elsewhere. The research team next turned to determining which geographical factors were causing the prevalence of the antibodies, with grants from the National Institutes of Health.

Linked to Tick Bites

The team found that a large majority of individuals who had the specific antibodies which caused allergic reactions to alpha-gal reported tick bites within weeks or months of the onset of allergic symptoms. Upon investigation, the researchers found that more than 90 percent of the patients in their alpha-gal allergy database had tick bites. Although that was not conclusive, the strong correlation between tick bites and the alpha-gal allergy-causing antibodies merited further study.

Alpha-Gal Allergy to Meat

The team also found that the same antibodies were linked to a novel allergic reaction that they called “delayed anaphylactic shock.” Three to six hours after eating certain types of meat, including beef, pork, and lamb, individuals with alpha-gal allergy experienced severe reactions. The delay in the reaction after consuming meat makes the allergy particularly difficult to diagnose. Valet states that it is possible that only 10 percent of alpha-gal allergies have been diagnosed due to the recent discovery of the allergy and its unique characteristics.

Oddities of Alpha-Gal Allergy

Most current research on anaphylaxis states that the reaction begins within minutes, or even seconds, of exposure to an allergen. Most allergens are food proteins, pollen, dander, or venom. Further, the onset of allergies is usually during childhood. Alpha-gal allergies, which do not begin promptly after exposure, are not usually present during childhood, and are not caused by food proteins, are particularly novel to allergists. The idea of alpha-gal, a sugar, being an allergen alters the field of study. Similarly, the delayed onset of reactions to alpha-gal, taking several hours before onset, is called a “paradigm altering discovery” by Platts-Mills.

Lone Star Tick

Eventually, researchers determined that bites from the lone star tick are a cause, and possibly the only cause, of the specific IgE antibodies that create alpha-gal allergy. They believe that something in the lone star ticks’ saliva causes humans to begin production of the IgE antibodies, which eventually will cause allergic reactions to alpha-gal in meat. These ticks, found mostly in the Southeastern United States but in an increasing geographic range, are most active in warmer months and tend to live in wooded areas. All of the research so far indicates that alpha-gal allergy is permanent and has no cure. Once exposed, an individual will be allergic to alpha-gal, and therefore, to beef, pork, venison, lamb, and other meats, for the remainder of his or her life. Additionally, researchers have found that repeated exposure to lone star tick bites can increase the severity of the reaction.

Avoiding lone star tick bites is the only way to protect against alpha-gal allergy. The Centers for Disease Control suggest the following:

  • Avoid wooded and bushy areas with high grass and leaf litter.
  • Walk in the center of trails.
  • Use repellents that contain 20 to 30% DEET (N, N-diethyl-m-toluamide) on exposed skin and clothing for protection that lasts up to several hours. Always follow product instructions. Parents should apply this product to their children, avoiding hands, eyes, and mouth.
  • Use products that contain permethrin on clothing. Treat clothing and gear, such as boots, pants, socks and tents. It remains protective through several washings. Pre-treated clothing is available and remains protective for up to 70 washings.
  • Other repellents registered by the Environmental Protection Agency (EPA) may be found at http://cfpub.epa.gov/oppref/insect/.