When you say “fire ants,” people likely think about the bad news — painful stings, itching, and damage to crops. But some University of Virginia researchers now say the presence of this invasive insect species might also have an upside: reducing prevalence of red meat allergy caused by tick bites.
Jeffrey Wilson, MD, PhD, and Behnam Keshavarz, PhD, of the university’s division of allergy and immunology, didn’t start out trying to study the fire ant. “Our interest is in α-gal,” or IgE antibodies specific for the oligosaccharide galactose-α-1,3- galactose, Wilson said in a phone interview.
Discovered about 10 years ago by another paper co-author and University of Virginia colleague, Thomas Platts-Mills, MD, PhD, α-gal syndrome describes patients who have developed delayed urticarial or anaphylactic reactions to red meat. It helped explain many cases of otherwise mysterious cases of anaphylaxis, in individuals with no exposure or sensitivity to common allergens. Subsequent research linked the allergy’s development to tick bites — in particular, from Amblyomma americanum, the so-called lone star tick.
The group’s intent was to complete “a cursory epidemiology of α-gal syndrome in the U.S., to see where it’s distributed,” Wilson told MedPage Today. As explained in the Journal of Allergy and Clinical Immunology, that led them to the fire ants.
To examine the allergy’s prevalence, during 2016-2017 the authors contacted 152 allergy clinics in 44 states and one Canadian province to find out their experience with α-gal. “We were just asking them, were they aware of the α-gal allergy, and then asking them were they seeing cases, and if so, how were they diagnosing them and how many cases were they seeing,” Wilson explained. “We did all these interviews, kept spreading the tree out — we kind of started locally and kept branching out so we had pretty good coverage across the whole country.”
The authors found that at least one provider in each of 11 states had seen 100 cases of the allergy. “These states included Arkansas, Virginia, North Carolina, Tennessee and Missouri, as previously reported, but also Alabama, Kentucky, Georgia, Maryland, Oklahoma and New York,” the authors wrote. “Of the 29 providers who reported greater than 40 cases, 28 were in the area where A. americanum was reported to be present in 2007, and none were west of the 100th meridian.”
Oddly, though, “many of the clinics close to the Gulf Coast had seen few or no cases despite being within the reported range of A. americanum. For example, of 10 practices surveyed in the eastern half of Texas, none reported more than five cases and six reported no α-gal cases at all,” the group’s paper reported. Given that Texas is the Lone Star State, that drew the researchers’ attention — especially when they learned that entomologists had previously found an inverse relationship between populations of lone star ticks and invasive fire ants.
The latter are common in a band stretching across the southern U.S., from Virginia to California. Researchers with the U.S. Department of Agriculture posted a map in 2017 indicating their range could be substantially wider, encompassing much of the middle U.S. and extending up through Washington state.
Why would more fire ants mean fewer lone star ticks? As allergists and not entomologists, “we’re only hand waving in this part; our paper doesn’t explain why,” Wilson said.
Entomologists have proposed some mechanisms, he added. For example, data from the 1970s suggest that fire ants could be predators of ticks, while more recent papers suggest a more indirect effect. One idea was that fire ants may be toxic to small mammals, and because of that, “mammalian reservoirs can be depleted or lessened,” meaning less food for the ticks, said Wilson.
Another theory was that fire ants may modify tick behavior, so that the ticks aren’t as active. Or “it could be some combination of these things,” he said.
One surprising finding of the paper was a cluster of meat allergy cases in the northern part of Minnesota, near Duluth. “The lone star tick is thought not to be established that far north…. That raises the question, is the lone star tick present a little more than people think, or it possible a different kind of tick is causing problems up there?” he said.
The group’s paper noted that “different species of ticks cause α-gal sensitization outside of North America, e.g., Ixodes ricinus in Europe and Ixodes holocyclus in Australia, and it has been recently reported that Ixodes scapularis (the black-legged tick) can express α-gal epitopes.”
“Because I. scapularis and Dermacentor variabilis are present in northern Minnesota, it is possible that these ticks could be relevant to α-gal sensitization,” it continued. “On the other hand, the scarcity of α-gal cases in other areas where these ticks are common, including the northeastern U.S. in the case of I. scapularis, suggests that these species of tick are not a major cause of sensitization.”
The authors noted several limitations to their study, including the difficulty in surveying for the allergy when there isn’t an ICD-10 diagnostic code for it, and that case numbers could be subject to recall bias. In addition, some cases were diagnosed and/or acquired when patients were in a different part of the country.