Human Helminths and Allergic Disease: The Hygiene Hypothesis and Beyond

Abstract

Abstract. There is much debate about the interaction between helminths and allergic disease. The "Hygiene Hypothesis," a very popular concept among scientists and the lay public, states that infections, especially during childhood, can protect against allergic diseases. Indeed, helminth infections are known to induce regulatory responses in the host that can help the control of inflammation (including allergic inflammation). However, these infections also induce type-2-associated immune responses including helminth-specific IgE that can cross-react against environmental allergens and mediate IgE-driven effector responses. Thus, it is the delicate balance between the parasites' anti-and pro-allergenic effects that define the helminth/allergy interface.The immune system has evolved, in large part, through its interaction with microbes and parasites, an interaction that drives specific or specialized immune responses to deal with the widely varying groups of microorganisms. For example, parasite-derived induction of interleukin (IL)-4, IL-5, and IL-13 coordinate the prototypical responses to metazoan helminth pathogens, 1 whereas viral-and bacterial-specific induction of Type 1 and Type 2 interferons are required for control of these types of infections.

Soil‐transmitted helminth parasites and allergy: Observations from Ecuador

“…The presence of anti‐ Ascaris IgE was associated with IgE sensitization to aeroallergens, an effect that might be mediated by a higher degree of atopy among wheezy/asthmatic children exposed to ascariasis or by a direct effect on airways reactivity caused by inflammation consequent to the host response to the presence of Ascaris larvae migrating through the lungs . Alternatively, the association between anti‐ Ascaris IgE and wheeze could be explained by cross‐reactivity between IgE epitopes of parasites and aeroallergens . Mite atopy appeared to explain a greater proportion of wheeze in urban compared to rural schoolchildren and in a population of asthmatics with a low prevalence of STH, the association between anti‐ Ascaris IgE and acute asthma disappeared after controlling for mite IgE .…”

Parasites and allergy: Observations from Africa

“…We identified relevant publications through searches conducted in PubMed using keywords related to “allergy” or “hypersensitivity” in combination with “helminths,” “parasites,” or “worms” and “Africa (South of the Sahara and Northern Africa).” Our search was restricted to human studies reported in the English language that were published between January 2008 and March 2018. The search was limited to the last decade to highlight new and recent findings in the literature given that older observations have been covered extensively elsewhere …”

Worms: Pernicious parasites or allies against allergies?

“…For example, while hookworm infections were associated with a protective effect against asthma, other helminths like Trichuris trichiura , Enterobius vermicularis and Strongyloides stercoralis did not show any effect, and conversely Ascaris lumbricoides infection increased the risk of developing asthma and wheeze . Greater consensus was observed regarding protection to atopic sensitization and allergic skin reactivity, although the outcome varied with the allergen studied …”