Epidemiology is the study of health patterns in society, and for bioarchaeologists this is an important aspect of study. For paleoepidemiology to be effective it requires not only a wide sample of the skeletal population but also an understanding of the archaeological and environmental context. Without the context we cannot begin to explain the causes for the patterns of disease and health. Due to this, paleoepidemiological studies require an interdisciplinary viewpoint that combines modern knowledge of disease with past contextual knowledge. Hibbs and colleagues (2011) recently published a paleoepidemiological study of Schistosomiasis in Ancient Egypt that takes this type of approach.
Hibbs et al. (2011) argue that the examination of Schistosomiasis prevalence among two different early Christian (350-750 CE) cemeteries from Egypt has revealed a correlation between the infection and the use of saqia irrigation. Schistosomiasis is a parasitic infection that is most commonly water-borne. While the mortality rate for the infection is fairly low, it is a chronic infection that can cause damage to internal organs, impair growth and impair cognitive development. It is extremely prevalent even today in Africa, Asia and South America. The parasite is transmitted through excrement in water, so it is often associated with the problems of developing nations and areas lacking clean water. It can also be carried by host snails, which require a constant aquatic environment. This means that the disease is more prevalent in areas where there is a constant source or water.
It is this connection with the snail hosts that led researchers to look into the connection with irrigation practices. For thousands of years, irrigation along the Nile was provided by the yearly flooding cycles. This practice is called seluka cultivation. However, there was a shift to saqia irrigation, which used an ox powered waterwheel to raise the waters of the Nile to irrigation canals and fields. Hibbs et al. (2011) argue that it was this agricultural transition which caused the rise of Schistosomiasis in ancient populations. Natural flooding does not support a favorable habitat for the host snails, and prevent the transmission of disease. However, the use of irrigation canals does support snails. These canals allowed for Schistosomiasis to become more prevalent by bringing humans into more constant contact with the disease argues Hibbs et al. (2011).
In order to test this, mummified remains were taken from two early Christian cemeteries in Egypt: Wadi Halfa and Kulubnarti (550-950 CE). Both samples contain individuals from all age groups and are representative of both sexes. A chemical process using assays was employed to test for the presence of circulating cathodic antigens (CCA) in the mummified tissue. The amount of CCA in the tissue is reflective of the infection of Schistosomiasis in the individual. They calculated the presence of Schistosomiasis by separate cemeteries and by the population subgroups for age and sex. They found that overall prevalence of Schistosomiasis was 25% in the Wadi Halfa population and only 10% in the Kulubnarti population. There was no difference by sex in prevalence. In the Wadi population adults were more likely to have infection, whereas in the Kulubnarti population older children were more susceptible.
In order to understand these differences, Hibbs et al. (2011) take a sociocultural and contextual approach. The main difference between the Wadi Halfa and Kulubnarti population is that the former has more irrigation than the later. In modern populations, the parasite is more often found in developing nations where the problems of living in close proximity to standing water have not yet been resolved. The authors hypothesize that this is what was occurring to the Wadi population. Archaeological evidence supports that the Wadi population had implemented the saqia method of irrigation, whereas there is no archaeological evidence of irrigation at Kulubnarti. This helps with more general comparisons of the two populations, because infection can cause a multitude of problems which affect the daily lifestyle of the individuals. Future studies, argue Hibbs et al. (2011) will include a full report on the health of these two populations to complete the picture.
Studies like this are fascinating, not only because they are able to connect archaeology and bioarchaeology to understand prevalence of disease, but because they also integrate modern medical anthropology into their research. Understanding how the disease affected individuals in the past can also be beneficial for medical anthropologists because they can have a better idea of how the disease historically affected people: its prevalence, the demographic group affected and how it was transmitted. The connection of disease to culture is extremely important for understanding causality, and also extremely fascinating!
Hibbs, Secor, Van Gerven, and Armelagos 2011. Irrigation and Infection: The Immunoepidemiology of Schistosomiasis in Ancient Nubia. In American Journal of Physical Anthropology 145