Pestology Blog

Over the last few years, the odd tick-borne illness known as alpha-gal syndrome (AGS) has become more common. This is the allergy that turns a bite from the lone star tick (Amblyomma americanum) into a lifelong, potentially life-threatening, allergy to red meat. For carnivores, this sounds like something out of a bad horror movie. Luckily there was comfort in the fact that the likelihood of contracting this illness was seemingly low. In 2022, the CDC estimated up to 450,000 people in the US (only 0.14% of the U.S. population) had the condition. But a new CDC surveillance report suggests the number of people carrying the antibodies behind this terrifying meat-allergy may be a lot bigger than we previously thought. 

For anyone not already aware, here’s a quick refresher on how this tick-borne illness works. Alpha-gal is a sugar molecule found in mammalian meat, dairy, and other animal byproducts like gelatin. It's also present in tick saliva, and when a lone star tick (or possibly other tick species, but that’s a whole separate BugBytes episode) feeds on a person, it can trigger their immune system to start producing immunoglobulin E (IgE) antibodies against that Alpha-gal sugar. From that point on, eating pork, beef, or lamb can set off an allergic reaction, sometimes hours after the meal, which makes AGS notoriously tricky to diagnose. To make things even more complicated, plenty of people carry the antibodies without ever developing symptoms. So, nobody really knew how common alpha-gal IgE actually is at the population level, suggesting that the CDC’s 2022 report may have underestimated the condition across the US.  

To get a better handle on that number, the CDC worked with a team of university and blood-bank researchers to test 3,000 residual blood donor samples collected between November 2024 and April 2025 from 10 states: Arkansas, Kentucky, Maine, Minnesota, Missouri, New Mexico, South Carolina, Tennessee, Virginia, and Washington. Half of those states were chosen because they'd historically reported high numbers of suspected AGS cases, while the rest served as points of comparison, including a couple of states well outside the lone star tick's known range. Every sample was run through a lab test that detects alpha-gal-specific IgE, and the results were weighted to consider each state's actual age and sex demographics. 

Unsurprisingly, the findings tracked almost exactly with the lone star tick’s known distribution. Arkansas topped the list at an estimated 31.2% seroprevalence, followed by Missouri at 26.0%, with Virginia, Kentucky, and Tennessee all landing in the low-to-mid 20s. Combined, those five states came in at 24.0%, meaning roughly one in four adults there could test positive for alpha-gal antibodies. On the flip side, Washington and New Mexico, both outside the lone star tick's established range, barely registered above 1-2%. Older adults, men, and non-Hispanic individuals all showed higher odds of seropositivity, and people living in less densely populated counties were more likely to test positive than those in big cities, though positive donors still turned up in urban counties in several high-prevalence states. 

The part of this report that really matters for how we talk about AGS, though, is the distinction between being seropositive and actually having the syndrome. Carrying alpha-gal antibodies isn't the same as having a food allergy, and the researchers are careful to point out that only a small fraction of seropositive people ever develop clinical AGS. That means a positive IgE test on its own isn't enough to diagnose someone, and testing without matching clinical symptoms risks a wave of unnecessary diets and overdiagnosis. The authors are essentially asking clinicians and health departments to keep the two things separate: antibody data can point you toward where the risk is highest, but a real AGS diagnosis still requires the symptoms to match. 

For our PMPs out there, geography is a key takeaway from this report. The states with the highest estimated seroprevalence line up almost perfectly with established lone star tick populations, and the authors flag Maine as a state to watch since a documented case there was tied to a blacklegged tick (Ixodes scapularis) bite instead, hinting that the tick side of this story may not be limited to just the lone start tick going forward. As AGS becomes a reportable condition in more states, this kind of blood donor surveillance gives public health officials, and by extension the pest management industry, a clearer map of where tick bite prevention and client education are likely to matter most.