Another Crazy Thing Ticks Can Do


~ By a Family Medicine doctor in the US who hosts a Rare Diseases Page on SERMO

Last week the ticks in Central New York launched an all out assault. As I was nursing a particularly nasty bite than caused adjacent regional lymph nodes to balloon up, I couldn’t help but muse about tick-borne illnesses. And one of the weirdest isn’t an infectious disease at all. It’s an allergy to red meat that develops after the bite of the Lone Star tick. Sufferers develop gastrointestinal symptoms, itching, urticaria and sometimes anaphylaxis hours after eating a meal containing red meat. It turns out that affected individuals have IgE that reacts to the oligosaccharide galactose-alpha-1,3-galactose —alpha-gal for short.

Because the reaction occurs hours after eating non-primate mammalian meat, it’s not easy to make the connection for an individual patient. Truly fascinating is the tale of how the connection was made.

In 2004, during clinical trials of the monoclonal antibody cetuximab to treat metastatic colorectal cancer, some patients developed anaphylactic reactions to their initial infusion of cetuximab. This occurred mostly in patients living in certain southern U.S. states. Scientists determined that these individuals had IgE antibodies reacting to alpha-gal on the cetuximab molecule.

During this same time period, a group of patients was studied who spent a lot of time outdoors and had episodes of angioedema, generalized urticaria, or anaphylaxis. Some patients suspected their symptoms happened 3-5 hours after they ate meat. Most of the patients had been eating red meat for years without prior reaction. Most lacked past histories of allergies that would suggest an atopic tendency. Because the geographic distribution was the same as for cetuximab reactors, researchers looked for IgE to alpha-gal. Yes, the patients did have alpha-gal IgE.

By 2008, reports of delayed allergy to red meat were increasing. Researchers from Australia had previously suspected a relationship between mammalian meat allergy and tick bites. Many of the U.S. patients with acquired red meat allergy recalled tick bites, weeks or months prior to the start of their symptoms. A few patients had serum collected both before and after their tick bites. The post-bite sera demonstrated a 4-10-fold rise in IGE specific to alpha-gal. The geographic distribution of meat allergic patients and cetuximab reactors matched the distribution of the Lone Star tick Amblyomma americanum.

The exact mechanism for the connection isn’t known. There are three theories. Perhaps the ticks produce a substance in their saliva that is similar to alpha-gal. Or maybe they are injecting their hosts with mammalian derived glycoproteins or glycolipids that they picked up from a previous meal. A third possibility is that the reaction derives from some as yet unknown commensal species (a Rickettsia perhaps?) living in the ticks.

If someone does develop an allergy to red meat, the treatment is the same as for other similar reactions. Avoid the trigger, and use an epinephrine auto-injector if anaphylaxis happens.

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