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Invasive fire ants limiting spread of meat allergy

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Imagine never again being able to cut into a juicy steak or fry up some crispy bacon … at least not without breaking out in hives or having an anaphylactic reaction. That’s the nature of the the mammalian meat allergy, or what’s colloquially known as the alpha-gal allergy, which is spread through the bite of the lone star tick. But while this allergy is pervasive in the Southeast and the Mid-Atlantic, and is becoming more common in the Midwest and Northeast, some regions of the U.S. are seemingly immune to the otherwise aggressive spread of these ticks.

Credit for that can go to fire ants.

Invasive fire ants, which were accidentally imported from South America in the 1930s, are common in the Gulf Coast and Texas and are likely limiting a tick-acquired meat allergy in these areas, scientists report. Even moreso, the ants are moving northward and could reduce the prevalence of the red meat allergy in some Southern states. However, fire ant bites are also a cause of severe allergic reactions, so their spread isn’t without their own dangers.

The new research from the University of Virginia maps the extent of the red meat allergy in the United States, and it was reported in the Journal of Allergy & Clinical Immunology.

Researchers at UVa’s School of Medicine and their collaborators made the discovery while seeking to understand the scope of the “alpha-gal” meat allergy in the United States. 

“We did not set out to study fire ants, but when the number of alpha-gal cases in the Gulf Coast was consistently lower than we expected, the fire ant emerged as an interesting explanation,” said UVA researcher Behnam Keshavarz, PhD, a co-first author of a new scientific paper outlining the discovery.

Mapping the Meat Allergy

The meat allergy was first identified more than a decade ago by UVA’s Dr. Thomas Platts-Mills, MD, PhD, an internationally renowned allergist. Since then, he and his colleagues have shed light on how and why the tick’s bite causes people to develop allergic reactions to a particular sugar, alpha-gal, present in meat and other mammalian products. The symptoms can include itchy rashes, nausea and difficulty breathing. Severe reactions can progress to anaphylaxis if untreated.

platts-mills
The meat allergy was first identified by Dr. Thomas Platts-Mills, MD, PhD, an internationally renowned allergist. (Image by Dan Addison, UVA Communications)

Until now, there has been little examination of the geographic scope of the allergy in the United States. The UVA researchers set out to change that. They surveyed allergists across the country to map out cases of the meat allergy. They also tested blood samples from two different geographic areas where it was particularly prevalent. The latter was important to show that the allergy is “immunologically similar” across the country.

The researchers found the meat allergy was common in significant portions of at least 14 states. Eleven states had at least one allergist report more than 100 case in their practice: Alabama, Arkansas, Georgia, Kentucky, Maryland, Missouri, New York, North Carolina, Oklahoma, Tennessee, and Virginia.

In contrast, six of 10 allergy practices in Eastern Texas — the domain of the invasive fire ant — reported no cases of the meat allergy at all.

Weirdness in Minnesota

Oddly, there were an unexpectedly high number of cases in an area of Minnesota where the lone star tick is not thought common. Three separate providers in the northern portion of the state reported at least five cases of the meat allergy, with one reporting more than 40.

That, the UVA researchers note, may suggest there are more lone star ticks in the area than thought — or perhaps that another tick or even other parasite is spreading the meat allergy. Other species of ticks are known to cause the allergy outside North America.

“The best evidence is that lone stars are the dominant cause of the alpha-gal meat allergy in North America,” said co-first author Jeffrey Wilson, MD, PhD. “That said, we wouldn’t be surprised if other ticks, chiggers or even other kinds of parasitic organisms can occasionally contribute to allergic sensitization to alpha-gal.”

Fire Ants Marching

After collecting reports of the meat allergy from 44 states the researchers were surprised to see few cases in the Gulf Coast or Texas. This was unexpected because the lone star tick is usually reported on CDC maps in the area. After considering potential explanations, the researchers again surveyed many of the same allergists about allergic reactions caused by the fire ant. They overlaid their results, and the results showed a striking, inverse relationship: Areas with the most fire ant cases had the lowest presence of the meat allergy.

That suggests that the fire ants are either preying on or somehow competing with the ticks, limiting the spread of the meat allergy, the researchers say. They also identified an increasing number of allergy cases caused by the fire ants. This likely will continue as the fire ants spread north, they report.

The spread should help control the number of meat allergy cases in the Southeast and Mid-Atlantic, they predict. But it also likely will lead to an increase in allergic reactions caused by the fire ant.

“These are two arthropod-related allergic diseases that are connected with each other,” Platts-Mills concludes. “The situation is unique because we think we can predict how both will change over time.”

 

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