In this book we explore how different kinds of parasites affected the key civilizations that flourished across the world over the last 10,000 years. Ancient parasites can be recovered from mummies, skeletons, latrines, coprolites, and chamber pots. Analysis may involve microscopy, ELISA, proteomics, and recovery of DNA. A huge range of parasites can infect humans, ranging from helminths (worms), single-celled protozoa such as malaria and dysentery, and ectoparasites such as lice and fleas. Different parasites will have varying impact upon health depending upon the proportion of a society affected and the physiological consequences of infection upon the body. Here the concept of Disabilit-Adjusted Life Years (DALYs) is employed to estimate the health impact of parasites in past societies, and compare them. This should allow us for the first time to propose which past civilizations may have experienced the greatest health burden from the parasites affecting their populations.

In ancient China, Japan, and Korea it is clear that roundworm and whipworm were the most common parasites present. Where data are available to estimate how common these parasites were, they suggest that more than half of the population were infected. Flukes spread by eating raw fish and crustaceans were a significant health risk, but less than half of individuals appear to have been affected. These include Chinese liver fluke, Fasciolopsis, Gymnophalloides, Metagonimus, and Paragonimus. The range of species of flukes present seem to have been higher in Korea and Japan than China, which may reflect the range of species endemic there, or the range of foods traditionally eaten raw in each culture. Oriental schistosomiasis is contracted by wading in still freshwater, so farmers growing rice in paddy fields were at particular risk. Major trade routes such as the Silk Road have been shown to act as conduits for the spread of intestinal parasites across East Asia.

The most widespread evidence for parasite infection in medieval Europe is for species spread by poor sanitation, such as whipworm, roundworm, and the protozoa Entamoeba histolytica and Giardia duodenalis, likely related to the common use of human faeces as a crop fertilizer. The prevalence of infection by intestinal helminths has been shown to be at least a quarter to a third of the medieval population, with a broad north–south divide in the dominant types of parasite. While species spread by poor sanitation were present throughout the continent, in northern Europe where eating raw, smoked, dried, or pickled fish was common, fish tapeworm resulted. The use of dogs by farmers put them at risk of infection by Echinococcus granulosus as shown by calcified hydatid cysts. Human fleas and body lice helped spread the Black Death pandemic from the fourteenth century onwards. Medical practitioners thought intestinal worms were formed due to an excess of phlegm (one of the four bodily humours), while ectoparasites were formed due to putrefying humours, sweat, and grime. Delousing combs were widely used to remove head lice, while the wealthy in Italy applied mercury ointments to their hair.

A broad range of parasites were present in ancient Egypt and Nubia, with 15 different species, including ectoparasites, helminths, and protozoa. Some are spread directly from one person to another (such as pinworm and head lice), some pass through animals as part of their life cycle (such as Taenia tapeworms, fish tapeworm, and trichinella), while others require biting insect vectors to spread them (such as malaria, leishmaniasis, and filariasis). Around 40% of ancient Nubians had head lice, 10% of Nubians were infected by visceral leishmaniasis, 22% of Egyptian mummies were positive for malaria, and 17% were positive for schistosomiasis. As malaria and schistosomiasis cause chronic anaemia and fatigue during physical work, they must have been responsible for a considerable drain upon the capabilities of the workforce in these civilizations along the Nile.

When we consider intestinal parasites, early societies to the east of the Andes were mainly infected by hookworm, whipworm, and to a lesser degree roundworm, thorny-headed worm, and Echinostoma. In contrast, to the west of the Andes fish tapeworm and pinworm were the dominant intestinal parasites, with lower levels of hookworm, dwarf tapeworm, and roundworm. This variation between cultures on either side of the Andes may indicate different approaches to sanitation, as well as the contrasting climate with high rainfall in the east and arid climate to the west. Head lice were found in 60–80% of mummies from Pacific coast societies such as the Chinchorro. Chagas’ disease, spread by the bite of bed bugs, affected 40–50% of Pacific coast civilizations including the Chiribaya and Inca. This causes a slow death from heart failure and intestinal failure. Mucocutaneous leishmaniasis spread by sandfly bites was also endemic in civilizations along the Pacific coast, causing ulcerating destruction of the face.

The earliest evidence of parasite infection in the prehistoric peoples of Europe show roundworm and whipworm infection in Palaeolithic and Mesolithic France, Sweden, and Britain. In the Neolithic period and Bronze Age those farming crops and herding animals on dry land were mainly infected by roundworm and whipworm. The protozoan Entamoeba histolytica, which causes dysentery, was also found at a number of Neolithic sites. In contrast, those living in lakeside villages built on stilts were commonly infected by fish tapeworm, Echinostoma fluke, and giant kidney worm, which are all contracted by eating raw freshwater foods. This shows how the lifestyle led by ancient peoples affected the types of parasite to which they were at risk. Environments that preserved clothes well, such as the Iron Age salt mines in Austria, resulted in the recovery of large numbers of body lice, which suggests that ectoparasites were also common.

Despite major investment in sanitation infrastructure, intestinal parasites spread by faecal contamination of food and water were a particular problem everywhere in the Roman world. Similarly, ectoparasites such as lice and fleas were common despite the Roman enthusiasm for washing in communal bathhouses and the use of delousing combs. However, some parasites seem to be much more regional in their distribution, likely due to climate variations. Fish and Taenia tapeworms, spread by eating raw or undercooked fish, pork, or beef were more common in northern Europe than southern Europe, possibly due to the fact that the hot climate in the south made raw fish and meat go off faster than in the cooler north. In contrast, malaria seems to have been much more common in the Mediterranean region than in northern Europe, as the warm climate of the south created breeding sites for the Anophales mosquito, which transmitted the parasite. Roman period medical texts by Galen and other physicians showed awareness of a number of parasites and tried to explain them in the context of the humoral theory. Treatment involved trying to rebalance the humours in order to return the individual to health.

Early communities of the Arctic, subarctic, and north-west coast were most at risk of fish tapeworm infection, as these societies relied heavily on fish in their diet. In the north-eastern and south-eastern woodland regions early populations living around the Great Lakes would also have been at risk of fish tapeworm infection. Those communities living further south, especially those engaging in farming, were prone to parasites spread by poor sanitation including pinworm, roundworm, the protozoa Giardia sp. that causes dysentery, and possibly hookworm. Considering the early inhabitants of the great basin and arid south-west, populations were infected by pinworm at least by 7000 BCE, spread by close contact between group members in cave sites. Thorny-headed worm eggs may indicate the consumption of crickets as part of the early hunter-gatherer diet in these communities. With the introduction of agriculture we see an increase in the range of parasite species present, to include whipworm, roundworm, dwarf tapeworm, and taeniids. As population size and density increased, we find a progressive increase in pinworm (30–70% of coprolites in some communities) and head lice (44% of mummies).

In the ancient Near East the most successful intestinal parasites were whipworm, roundworm, Taenia tapeworm, and pinworm. While roundworm and whipworm are commonly found in early agricultural societies, the repeated presence of Taenia tapeworm in Near Eastern populations over time suggests that it was particularly suited to the climate and diet of the region. The presence of schistosomiasis at Tell Zeidan during the Chalcolithic period appears to be the earliest evidence so far identified for the invention of a new technology by humans increasing the risk of spread of an infectious disease. Agricultural irrigation was first developed in the Near East around 7500 BCE, and these irrigation systems allow breeding of the water snails that can spread the schistosomiasis when people wade through areas of standing freshwater. Head lice and body lice were also present in the region, and head lice in particular seem to have been present from the earliest prehistoric populations there. The development of wooden delousing combs, coupled with the arid climate that preserved them, has resulted in a strong body of evidence for head lice and their eggs.

We have seen that different species of parasites have markedly different impacts upon health. Some may kill their host and so reduce the population size, others cause chronic anaemia or malnutrition and so reduce their physical productivity, while the remainder may cause symptoms that reduce psychological well-being or cause no symptoms at all. If we use disability-adjusted life years to compare the impact of parasites upon different ancient civilizations, we can estimate the degree to which each were burdened by parasite infection. Using this approach would suggest that the civilizations with the heaviest health burden from parasites were (1) Egypt and Nubia; (2) Roman Empire; (3) Ancient China, Korea, and Japan; (4) South American Pacific Coast civilizations such as Maya, Moche, and Inca; and (5) the Ancient Near East. As many parasites impair the ability of labourers to complete physically arduous work, it is possible that the need for new, healthier workers to complete national infrastructure projects may have triggered military expeditions to neighbouring states to obtain prisoners to work as slaves in many of these civilizations.

We have explored some of the ways in which parasites can tell us about past human migrations. Sometimes an expansion to the endemic area of a parasite shows that migration had found an environment receptive to that species’ life cycle. Examples date across evolutionary time, from lice in our hominin ancestors to transatlantic slavery in the last few hundred years. In contrast, in many more examples the parasite failed to become endemic in the new region due to the lack of key elements required for its life cycle. The role of human ectoparasites in the spread of epidemic and pandemic disease has been vitally important throughout human history. As humans move they take their ectoparasites with them, their bodies acting as an incubator for bacterial infectious diseases. While bubonic plague is certainly the best recorded and researched of these epidemics, many others such as epidemic typhus and trench fever would have caused disease and death in past societies. Although human fleas and lice in themselves have only limited impact upon health, it seems likely that far more of our ancestors have died from diseases spread by their ectoparasites than ever died from intestinal parasites.