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Tick Bite and Meat Allergy: Blood Meal May Not be Required

SAN FRANCISCO — Allergic reactions to red meat are on the rise, and the spread of the antigen that causes meat allergies may be easier than previously thought, researchers reported here.

Alpha gal syndrome (AGS) describes an allergic immune response to the alpha gal sugar found in the blood of nearly all mammals except humans, which manifests as a sudden allergic reaction to red meat.

Caused by tick bites — specifically the bite of the Lone Star tick species — it has been widely believed that in order to trigger the allergic response in humans, the bite would have to come from a tick that had recently fed on the alpha-gal-rich blood of a deer, dog, or other lower mammal.

But that may not be the case: Scott Commins, MD, PhD, of the University of North Carolina at Chapel Hill, and colleagues, found that ticks can induce the immune response in the absence of an alpha-gal blood meal. Commins presented the data at a poster session at the American Academy of Allergy, Asthma & Immunology (AAAAI) annual meeting,

The findings suggested that any bite from the Lone Star tick may result in the allergy, he told MedPage Today.

“We’ve been trying to figure out what it is that the tick does to create or shift that immune response. The idea has been that a tick bites a deer or dog and picks up alpha-gal from blood meal,” he said. “Our data suggest that this may not be true. It may be that tick saliva itself has immunomodulating properties that can shift our endogenous response.”

Commins was among the first clinicians to identify meat allergy in patients, and to link the allergy to the bite of the Lone Star tick roughly a decade ago. At the time, the tick was largely confined to the Southeast. Since then, more than 5,000 cases of AGS have been reported, as the range of the tick has expanded further north and into the central states of the U.S., Commins said.

Commins and colleagues exposed Lone Star ticks and other tick species, such as deer ticks and dog ticks, to blood meals from mammals whose blood contained alpha-gal and non-mammals without alpha-gal in their blood.

They showed that sensitization was independent of the blood meal source, but that it only occurred from tick salivary gland extract (TSGE) from the Lone Star tick.

To reach these findings, researchers stripped white blood cells of their Immunoglobulin E (IgE) antibodies produced by the immune system during an allergic reaction. The stripped white blood cells were then primed with plasma from individuals with AGS and without AGS and the researchers added tick salivary gland extract from four species of ticks – Lone Star, Deer, Gulf Coast, and American Dog — to the cells. Some of the ticks had recently fed on blood containing alpha-gal, and some had not.

They reported that frequency of CD63+ basophils was 40-fold higher when alpha-gal IgE-sensitized basophils were stimulated with TSGE from Lone Star ticks compared with baseline.

Also, extract from Ixodes scapularis (deer tick), but not the Gulf Coast tick (Amblyomma maculatum) also increased basophil activation.

IgE reactivity was found in tick saliva (mean 23.4 IU/mL61.9) among those with AGS but not larval tick or partially fed TSGE.

“The upshot of these findings is that we now have a much larger pool of tick bites to be concerned about because it doesn’t appear that the prior blood meal is important,” Commins said.

He added that while the Lone Star tick appears to be primarily responsible for cases of meat allergies identified in the U.S., other species are likely to blame for cases outside of the U.S. — Europe, Australia, South Africa, and Indonesia — where the tick is not found.

“This is an emerging allergy,” Commins stated.