Effects of treating helminths during pregnancy and early childhood on risk of allergy‐related outcomes: Follow‐up of a randomized controlled trial

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Allergy‐related diseases (ARD) such as asthma, eczema and rhinitis are commoner in high‐income countries (HICs) than in low‐ or middle‐income countries (LMICs), but their prevalence is increasing in the latter, where consequences can be more severe because of limited access to diagnosis, care and necessary treatment.1
Understanding exposures that “protect” against ARD in LMICs is important—for public health, and to provide insights into possible interventions for those at risk of ARD. Helminth infections are highly prevalent in LMICs, and immune responses to helminths and allergens are closely related. IgE and related effector mechanisms are likely to have evolved to protect mammals from helminths and ectoparasites,2 but parasitic helminths must survive for decades in their hosts, and have evolved a myriad of mechanisms to evade or suppress the host immune response.3 Animal models provide strong evidence that these mechanisms can protect the host against allergy‐related outcomes.4
In humans, the picture is more complex. Despite inverse associations between helminths and atopy, several trials have shown no, or little, effect of anthelmintic treatment on allergy‐related outcomes.4 One possible explanation is that early‐helminth exposure has long‐term effects, not mitigated by later treatment. In the Entebbe Mother and Baby Study (EMaBS), a randomized, placebo‐controlled trial of anthelmintic treatment during pregnancy, we showed a striking increase in the incidence of infantile eczema following maternal treatment with albendazole in a population with a high prevalence of maternal hookworm infection. We also observed an increase in eczema among infants of mothers with schistosomiasis who were treated with praziquantel.5 This was hailed as the first demonstration that treatment during pregnancy influenced ARD in the offspring.6
As eczema in early childhood may herald the development of asthma at school age, and as eczema and asthma may have a common link to atopy,7 we followed the EMaBS cohort to find out whether the prenatal intervention influenced risk of asthma and other allergy‐related diseases at age 9 years.
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