Using the front-door causal formula to control for confounding, this ecological county-level analysis found that higher white-tailed deer sightings in 2020 predicted greater Amblyomma americanum tick presence in 2024, which in turn predicted more self-reported alpha-gal syndrome (AGS) cases in 2025. Modeled scenarios suggest a 50%, 75%, or 100% increase in deer abundance would generate approximately 89, 126, or 159 additional AGS cases nationwide, respectively, with wide confidence intervals spanning as few as 6 additional cases at the lower bound.
AGS — an immune reaction to the carbohydrate galactose-alpha-1,3-galactose, triggered by lone star tick bites — causes red meat allergy and can produce severe anaphylaxis. It has gone from a curiosity to a genuine emerging public health concern, with CDC estimates suggesting hundreds of thousands of Americans may be affected, most undiagnosed. This study's causal pathway modeling is methodologically notable, but serious limitations temper conclusions: data relied entirely on citizen science observations rather than validated surveillance, the ecological design cannot establish individual-level causation, and the confidence intervals are strikingly wide. The absolute case counts also appear modest relative to estimated true prevalence, suggesting substantial underreporting. As a preprint not yet peer-reviewed, these findings require independent validation before informing wildlife or public health policy. Still, the work incrementally strengthens the biological plausibility of deer management as a lever for tick-borne disease control.