Written by: Ray Zhang
Edited by: Alejandro Cacho, Kristi Xing, Christia Victoriano
Illustrated by: Gefen Mor
From crab cakes to grilled salmon, seafood has become a quintessential part of the American diet. Along with Americans’ ever-increasing love for these delicacies, the number of individuals who are allergic to seafood has also been on the rise. From 2002 to 2019, the percentage of American adults with seafood allergies increased from 2.6% to 2.9% [1]. Moreover, a study on other food allergy rates across the globe has revealed that food allergies are not completely based on genetics—when and how the food is introduced to an individual can impact the development of allergic reactions [2]. These discoveries prompted researchers to look deeper into the impacts of environmental and socioeconomic factors on shellfish allergies. Specifically, scientists study shellfish, cockroaches, and dust mites, which all share the same allergen [3]. Sharing the same allergen signifies that if an individual was exposed to just one of these organisms at a young age, they could develop an allergic reaction to all three, drastically increasing their risk of ingesting life-threatening allergens. This article will explore the mechanism behind food allergies and the correlation between socioeconomic status, which includes factors such as income and education, and the development of shellfish allergies.
Behind the allergic reaction to shellfish is an abundant muscle protein called tropomyosin [3]. In arthropods, such as cockroaches and shellfish, tropomyosin is responsible for regulating muscle contractions, forming cytoskeleton structures in cells, and allowing proper bodily functions [4]. Since tropomyosin has a highly conserved evolutionary track, almost every animal, including humans, has this protein in their body [5]. This begs the question: if tropomyosin is so abundant in the human body, why does it induce an allergic reaction? The answer goes back to the genealogy of the protein where the conservative evolutionary track of tropomyosin results in a similarity of only around 50% to 60% between vertebrate and invertebrate species, a very low percentage considering that shrimp, cockroaches, and dust mites share 75 to 80% similarity [3]. During an allergic reaction, the body sees the normally harmless invertebrate tropomyosin as an invasive molecule and produces an antibody called immunoglobulin E (IgE) [6]. As IgE molecules are released, they bind to immune cells which produce a chemical called histamine, triggering common allergic symptoms such as swelling, itching, and hives [7]. Allergic reactions happen incredibly fast; in less than 30 minutes, the aforementioned symptoms can manifest. In severe cases, one might go into anaphylactic shock, a life-threatening allergic reaction that drastically lowers the blood pressure and closes up the throat, causing difficulty in breathing [8]. The fastest and most effective treatment for allergic reactions is an injection of the hormone epinephrine, which decreases the size of blood vessels, opens up the throat, and increases blood pressure [8]. Studying the relationship between cockroach exposure and shellfish allergy can inform individuals about their potentially deadly food allergy and help them prepare for unforeseen reactions.
In order to test the correlation between these three allergens, scientists drew data from large national databases and conducted statistical regressions on the information, which allowed researchers to determine the correlation between different variables. In one study, IgE values of 8,000 children who were confirmed to have different allergies through clinical diagnoses were analyzed [4]. Through regression models, the researchers found that shrimp allergy is significantly correlated with cockroach allergy, and there are no correlations with dust mites. Although the exact reasoning behind the lack of statistical correlation between dust mites and shellfish allergy is not outlined in the study, a possible explanation is that cockroach tropomyosin shares a higher genetic homogeneity with shellfish than dust mites. Moreover, when the researchers conducted another regression model with cockroach allergies removed to measure the impact of the variable, they noticed a decrease in shellfish allergy, implying that the decrease in shellfish sensitivity is influenced by the presence of a cockroach allergen [4]. But how does this exposure to cockroach allergen actually lead to the development of a shellfish allergy? Exposure to tropomyosin from the presence of cockroaches can confuse the immune system into thinking that the molecule is an allergen. This does not mean that every individual exposed to cockroach tropomyosin will develop shellfish allergy, rather, cross-reactivity between the two species may lead to increased likelihood of being allergic to shellfish because of the overlap in genetic expression of cockroach/shellfish tropomyosin. Although there have been previous studies on the correlation between cockroach, dust mite, and shellfish allergies, this is the first study that tracked the changes in response to these allergens in the US, solidifying the fact that shellfish allergy is connected to cockroach sensitivity [4]. These results are further corroborated in other studies of shrimp allergies in patients from rural China: being allergic to shrimp is correlated with cockroach allergies [9].
Studies have shown that children living in densely populated cities, specifically in areas where 20% or more of the households have incomes below the poverty level, have higher exposure rates to cockroaches compared to suburban peers [10]. In another study, researchers looked at the IgE values of 900 children in homes across the country where cockroaches were found and determined that socioeconomic status may mediate the high correlation between cockroach and shellfish allergies [11]. From the statistical analysis, scientists found that exposure to cockroaches at a young age drastically increased both shrimp and cockroach IgE values. Through a series of home visits and settled dust collections, researchers found that these children were likely exposed to cockroaches in bedrooms and television rooms. Though this study is correlational, the study suggested potential future areas of research regarding the intersection of race, age and socioeconomic status with prevalence of developing shellfish allergies from exposure to cockroaches [11].
It’s also important to note that children living in urban areas with asthma have exacerbated symptoms due to exposure to foreign substances such as pest allergens; the study even states that “cockroach allergens are major causes of urban pediatric asthma morbidity in the United States” [12]. Since prolonged exposure to cockroaches can lead to “higher asthma morbidity, including more hospitalizations, more medical visits, and more reported symptoms” and the individuals most likely affected by these pests are those living in lower socioeconomic neighborhoods, more public awareness about the comorbidity of shellfish allergy and asthma is crucial for addressing this socioeconomic disparity [13]. These results highlight an issue that goes beyond food allergies—disparities within the American income levels and geography heavily contribute to the overall well-being of Americans.
By studying the cross-reactivity of cockroach and shellfish allergies, scientists can gain a clearer understanding of how allergies are connected and provide crucial information on preventing the development of new allergies. These studies not only increased our understanding of tropomyosin but also provided a new perspective on the interconnectedness of different species. New treatments for allergy sensitivity will both increase patients' quality of life and decrease healthcare disparities. Above all, studying how socioeconomic conditions are connected to allergies underscores the importance of investigating socio-scientific issues.
References
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