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.

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.

The process of decision making is not linear and is affected by multiple factors, other than availability of evidence, such as political context, personal over public interests, decision makers’ accountability, relationships with stakeholders, and familiar experiences in the past. Evidence-informed decisions positively influence access, quality, efficiency, equity, and sustainability of health services, and improve transparency and accountability thereby reducing wastage, abuse, and corruption in the health system. This chapter presents six decision making tools that help policy makers and managers take evidence-informed decisions: burden of disease analysis; health technology assessment; cost-effectiveness analysis; health equity analysis; national health accounts analysis; and stakeholder analysis. The list of tools is not exhaustive, and additional tools can be explored to respond to the context and nature of the public health concern. Policymakers are not expected to know all their methodological aspects, rather they should know what tools are available, their purpose and application, strengths and limitations, and how to interpret the results in the local context.