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You are in a central Virginia ED seeing a 16-year-old boy with itchy hives, stomach cramps, vomiting, and mild angioedema of his lips. He is not wheezing, his vital signs are normal, and his airway is patent. His diet history is as follows: glass of orange juice and leftover cold pizza at 9am, half-pounder burger with bacon at noon, and a PB&J (which he eats daily) at 3pm. Symptoms developed at 3:30pm. Review of his medical records reveals that he was seen in urgent care for an embedded tick 1 month ago, and again for strep throat 8 days ago – he is on day 8 of 10 of amoxicillin to treat his strep throat. He received no antibiotic prophylaxis after the tick bite.
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August 14, 2024 at 1:14 pm
B) Burger and bacon
Alpha-gal syndrome is an allergy to the alpha-gal sugar found on the surface of some mammalian RBCs, and is associated with lone star tick bites. The pathophysiology is unclear, but the tick bite transfers alpha-gal into the person’s body, which in some people triggers IgE antibody formation. Alpha-gal syndrome commonly develops 4-6 weeks after a tick bite but may develop up to a year after. Symptoms upon eating foods with alpha-gal (“red meat allergy” = beef, lamb, pork products) develop 2-8 hours after the meal, and may produce anaphylaxis. Common symptoms are hives, angioedema, and GI (nausea, vomiting, diarrhea, cramps). Treatment is as for any allergic / anaphylactic reaction. Only a small minority of those bitten develop alpha-gal syndrome. Cases are highest in the Southeast and Midwest U.S. states, although sporadic cases have been identified even in places where ticks are uncommon. The timing of symptoms is right for an allergic reaction to peanut butter, but the fact that he eats this daily makes it an unlikely culprit. Amoxicillin can cause a non-allergic rash around day 7-8, but the rash is not hives nor associated with angioedema. The rash of Lyme disease, erythema migrans, is a targetoid rash that usually develops 3-30 days after the tick bite. Lyme disease is typically transmitted from the bite of an Ixodes tick, not a Lone Star tick – the geographic distribution overlaps but is higher in the Northeast for Ixodes.