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A consistent “shortage” of cases of the alpha-gal syndrome (AS) on the Gulf coast: possible relevance of fire ants as a predator of lone star ticks

      Rationale

      Allergic reactions to red meat in patients with IgE to alpha-gal are common in the southeastern U.S., but appear less common on the Gulf coast and into much of Texas. This contrasts with the reported distribution of A americanum (lone star tick). In addition, it has been known for many years that fire ants can kill ticks.

      Methods

      We carried out a survey of the prevalence of AS in allergy practices in areas where the fire ant has been present since 1974 (n=10), compared to areas of the Southeast without fire ants in 2000 (n=23). In a subset of clinics we additionally assessed reports of fire ant anaphylaxis (FAA).

      Results

      In keeping with the reported area of fire ants, few cases of FAA were reported in VA, KY, MO, OK, or northern AR. By contrast, there was a progressive increase in FAA cases through TN to the Gulf coast. A clinic in Montgomery, AL reported 100 cases of FAA and no cases of AS. A similar trend in reported FAA was identified in a north-south gradient from MO to TX. Cases of AS were much more common in clinics outside of the reported fire ant zone (χ2 10.5, P=0.001).

      Conclusions

      The geographic distribution of cases of FAA coincided with the known distribution of fire ants and the unexpectedly low incidence of AS. The likely explanation is that the fire ants have decreased the population of lone star ticks so that tick bites and sensitization to alpha-gal are no longer common in these areas.