Is wild-habitat disruption to blame for the increasing U.S. prevalence of Alpha-gal syndrome (AGS), a tick-borne allergy to animal meat? A University of North Carolina (UNC) at Chapel Hill modeling study is helping close in on this mysterious meat allergy that is on the rise.
An assistant professor in the infectious diseases division at the UNC School of Medicine and assistant professor of epidemiology in the Gillings School of Global Public Health, Ross Boyce, is collecting information from a network of sources to strategically determine where and how to battle ticks and other insects that can change a person’s life for the worse with one bite, UNC reports.
Using a dataset of 462 AGS patients with confirmed AGS from UNC Health and models based on environmental factors, such as landcover and topography, the team assessed whether the risk of AGS is linked to habitat fragmentation often seen in open spaces and areas of low-density development in North Carolina, South Carolina and Virginia.
What is AGS?
Bites from the lone star tick (Amblyomma americanum) or the blacklegged tick (Ixodes scapularis, also called deer ticks) can trigger AGS. Alpha-gal is a sugar molecule found in most mammals. After eating mammalian meat, people who become allergic to alpha-gal may experience an hours-long delay in symptoms, which include hives, swelling of lips, face, tongue or throat, stomach pain and nausea, UNC reports. It can also cause restricted breathing and death.
AGS has a particularly high incidence in the mid-Atlantic region. The number of suspected cases rose from 24 in 2009 to more than 34,000 in 2019. The only way to positively know a patient has the allergy is to test for antibodies that their bodies developed to fight the infection. Most people with AGS need to refrain from eating meat such as beef, pork, lamb, venison and rabbit.
“Reports of AGS have grown rapidly since its first report in 2009 and are likely to continue to increase as awareness of AGS and incidence of tick-borne disease more broadly increases,” the authors explain. “These increases are likely to be exacerbated by shifts in land use, resulting in more human-tick interactions throughout the southeastern U.S.”
Although clinical and laboratory diagnostics for AGS are becoming more readily available, the epidemiology of AGS, and tick-borne disease in general, apart from Lyme disease, is not well described.
AGS Risk Factors
The models identified low population density and open-space development as risk factors for AGS. Two models predicted a strong east-to-west risk gradient across the mid-Atlantic region, which largely reflects the environmental transition from mountains to coastal plains, while a third model predicted a much more uneven distribution.
“Understanding environmental risk factors associated with AGS diagnosis is a critical first step for determining at-risk populations, and here we show evidence supporting the hypothesis that AGS is associated with landcovers often correlated with the presence of Am. americanum,” the authors say.
Although the distribution of alpha-gal cases throughout the U.S. do not align exactly with the known distribution of lone star ticks, researchers say this suggests potential environmental confounders and/or ascertainment bias. However, estimating incidence and geographic case distribution is complicated by limited reporting as AGS is not generally reportable at the federal level and low healthcare provider awareness of the condition.
“AGS incidence, like all TBD (tick-borne disease), is largely driven by human behaviors that increase human-tick interactions, e.g., land use change, as opposed to tick population dynamics,” the authors wrote. “Anthropogenic land use change, such as forest fragmentation and urbanization in particular, have been linked to increased TBD risk.”
This study suggests the need for personal protection measures for individuals residing in, or entering, these at-risk areas.
These findings were published on April 23 in PLOS Climate.
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