Cum vermibus : worms in death diagnoses in the Liber Mortuorum of Milan from the late 15th to the late 17th century

Ascariasis remains one of the most prevalent parasitic infections worldwide, affecting an estimated 700 million people, particularly in tropical and subtropical regions. Although historically widespread across Europe, little is known about the epidemiological impact of ascariasis in medieval and early modern European cities. The frequent recording of deaths with worms (DWWs) in the Mortuorum Libri (Books of the Dead) of Milan (1452–1802) prompted us to assess the frequency and clinical manifestations of these fatalities. Across 9 annual registers spanning the late 15th to the late 17th century, 400 DWWs were identified. These cases were frequently characterized by a multitudo verminum (multitude of worms), a description that strongly supports a diagnosis of ascariasis. The proportion of DWWs among registered deaths ranged from 0.22% in 1629 to 4.36% in 1512. Notably, the year 1512, marked by military conflict and a plague outbreak, recorded an 8-fold increase in DWWs compared to preceding years, whereas the proportion of worm-related deaths remained stable during the 1630 plague epidemic. Common concurrent clinical manifestations were fever (30% of cases) and epilepsia (57%), which in contemporary medical terminology referred to an intrinsic childhood neurological weakness. Children aged 1–5 years accounted for the majority of DWWs, reflecting the high mortality in this age group throughout the centuries considered and the vulnerability of young children to parasitic infections. This historical analysis provides valuable insights into the disease burden of Ascaris lumbricoides as documented by contemporary physicians, demonstrating the frequent clinical recognition of ascariasis in early modern Europe.