Abstract

The complex microcosm of bacteria, viruses, fungi, and parasites that live on and within the human body is known as our microbiome. As part of that microbiome, we will discuss the evidence for parasites in crusaders who travelled to the eastern Mediterranean during the twelfth and thirteenth centuries. Crusader period manuscripts recorded outbreaks of dysentery during military expeditions, and explain how those with dysentery might be managed in a military order infirmary. Clergy on crusade could interpret such epidemics as God enacting his will upon the army, either as a reward or punishment. Medieval medical texts also describe the physical shape of different intestinal worms, beliefs about how intestinal worms were formed, and their medical treatment. Moreover, laboratory analysis of excavated latrines at crusader sites in the kingdoms of Jerusalem and Cyprus has identified roundworm, whipworm, fish tapeworm, beef/pork tapeworm, and the protozoa Entamoeba histolytica and Giardia duodenalis that cause diarrhoea and dysentery. The life cycle of these parasites helps us to understand the effects of sanitation and the consumption of meat and fish that can spread parasites to humans. We will also consider the ways in which a heavy burden of these parasites can lead to disease or death, especially on a military expedition.