I PARASSITI NELLA STORIA DELL'UOMO: INFEZIONI DEL PASSATO, MALATTIE NEL PRESENTE

This article will present the concept of evolutionary mismatch, in relation to the reduction in the circulation of pathogenic (or quasi-pathogenic) microorganisms and macro-parasites in human populations, throughout human and pre-human history. In particular, we will refer to the variegated community of parasites and microorganisms, prokaryotes or eukaryotes, pathogenic or only marginally or occasionally pathogenic, which evolved as inhabitants of our bodies together with us human beings and our ancestors. For simplicity, we will generically refer to these organisms as parasites. These organisms, once present endemically in the populations of our species, are believed to have developed a complex network of interactions with our physiological systems, particularly with regard to stimulation of the immune system. In this dynamic, the host organism, in turn, would have evolved countermeasures to the chronic presence of parasites, with a bias towards the modulation of the immune response, somehow specific for the different types of stimulation determined by the parasites. The drastic reduction in the circulation of parasites in industrialized societies would therefore have left an imbalanced immune system behind it. According to this view, which we can refer to as the “hygiene hypothesis”, the increase in the incidence of various immune-mediated diseases in industrialized countries would be attributable, at least in part, to this imbalance of the immune function.