α-Gal IgE in the developing world: not just tick bites
Published: February 1, 2021
A form of mammalian meat allergy, commonly called the “α-Gal syndrome”, has been widely reported in parts of the United States, Australia, Europe and Asia. In these areas it is thought that individuals develop the allergy as a consequence of tick bites, with the lone star tick (Amblyomma americanum) being the major culprit in North America. The α-Gal syndrome is caused by IgE antibodies that recognize a sugar present in muscle and other tissues of non-primate mammals - galactose-α-1,3-galactose (α-Gal). Measurement of α-Gal IgE antibodies in blood samples plays an important role in diagnosis. Interestingly, a few reports have suggested that α-Gal IgE antibodies are very common among individuals who live in rural areas of the developing world. The explanation and significance of α-Gal IgE in such settings, where mammalian meat allergy is not a widely recognized problem, has been little studied.
As recently reported by Wilson et al in The Journal of Allergy and Clinical Immunology (JACI), here the research team built on earlier work that described a high frequency of α-Gal IgE among grade-school age children that lived in largely rural parts Ecuador and Kenya. Although the children were originally recruited as part of asthma studies, information about diet, geohelminth parasite burden and environmental exposures were available for the children from Ecuador to help the investigators look for risk factors that could explain the cause of α-Gal IgE. Using the standard blood test, α-Gal IgE was measured in serum from 599 children who lived in a tropical area of Ecuador and 254 children who lived in a subtropical area of Kenya. The results were compared with children from Virginia who had α-Gal syndrome and also a group of children from Virginia without known food allergies.
Detectable levels of α-Gal IgE were measured in blood samples from 32% of the children from Ecuador and 54% of the children from Kenya, but the mean levels were lower than in the children from Virginia who had mammalian meat allergy. In both Ecuador and Kenya, the presence of α-Gal IgE was associated with rural living and markers of prior parasitic infection. Despite the high frequency of α-Gal IgE, in Ecuador 87.5% of the children ate beef at least once a week, including over 75% of the children who had α-Gal IgE levels that were comparable to the levels observed in Virginian children who had meat allergy. Information about tick bites was not available, but the investigation revealed that antibody markers of prior exposure to Ascaris roundworms, but not other endemic parasites, were associated with the presence of α-Gal IgE. A connection between α-Gal IgE and chronic geohelminth parasitism was also hinted at by higher levels of a different antibody subclass to α-Gal – IgG4.
Overall, the study suggests possible explanations for the surprising observation that α-Gal IgE is very common in parts of the developing world that do not have a recognized epidemic of mammalian meat allergy. First, the levels of α-Gal IgE are relatively low as compared to individuals from the USA who have the α-Gal syndrome. This is consistent with other forms of food allergy where relatively low IgE levels do not necessarily equate with clinical allergy. Secondly, in areas where geohelminth parasites are endemic α-Gal IgE may be primarily caused by Ascaris roundworm infections rather than tick bites.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.
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