Human allergy and geohelminth infections: a review of the literature and a proposed conceptual model to guide the investigation of possible causal associations.

Geohelminth infections and allergic disease are major public health problems and there is evidence in developing countries that they are associated. Although there is an extensive literature of the relationship between geohelminth infections and allergy, there is little consensus on whether the association is causal and if so, whether geohelminth infections may increase or decrease the risk of allergy. An explanation for the conflicting findings of epidemiological studies is that geohelminths decrease the risk of allergy in areas of high infection prevalence and increase the risk of allergy in areas of low prevalence. Chronic geohelminth infections are inversely associated with allergy and anthelmintic treatment may increase the prevalence of allergy. In this paper, we review studies that have investigated the relationship between geohelminths and allergy; discuss the relevance of prevalence and timing of geohelminth infections and propose a conceptual model to define relevant scientific questions in future human and animal studies.