A case study of water-associated disease in Ecuador illustrates the need for and application of the proposed approach. With the goal of providing transportation faster and cheaper than river boats, the Ecuadorian government built a 100-km road between the southern Colombian border and the Ecuadorian coast from 1996 to 2001. After completion of the main road, secondary roads continued to be built that linked multiple villages to the main road. This roadway network led to major changes in both the social structure and ecology of the region (Sierra 1999
). Although there is evidence that road construction affects the incidence of vector-borne and sexually transmitted diseases (Birley 1995
), impacts on diarrheal disease remain poorly understood. Further, although transmission of enteric pathogens has been linked to proximal factors of water quality, sanitation and hygiene practices, the relationship between distal social and ecologic factors (e.g., increased population density and regional scale water patterns) and diarrheal disease remains poorly understood (Curriero et al. 2001
To help understand road construction related diarrheal disease, Eisenberg et al. (2007)
mapped a suite of distal environmental changes that can affect proximal environmental characteristics, which in turn can affect the transmission of enteric pathogens. Their framework incorporates processes at multiple spatial and temporal scales using regional, villagewide, individual, and molecular-level data. These data can be integrated using systems approach. To demonstrate the system’s complexity, multiple outcomes, and the potential for unanticipated consequences, consider how road construction can affect diarrheal disease prevalence: Roads can lead to deforestation, which subsequently affects watershed hydrology, local climate, and pathogen transmission () (Curriero et al. 2001
). Roads also increase flows of consumer products, material goods, and medicine and potentially improve access to health care facilities and health information. At the same time, short-term travel patterns are intensified, introducing pathogen strains into the communities. The population density in both existing and new communities created along the new roads can rapidly increase, but water supply and sanitation infrastructure frequently lags, thus increasing the likelihood of transmission of enteric pathogens. Similar changes can also be produced by dams, urbanization, agricultural practices, deforestation, and climate change.
Example of distal, medium-term, and proximal components in the water-related infectious disease cycle in the Ecuadorian case study.
Interventions at multiple points in the cycle and at different temporal and spatial scales can break the pathogen transmission cycle. For example, shows that although road construction and the resulting deforestation are linked to disease transmission, these medium-scale drivers are ultimately linked to distal drivers, such as country-level economic conditions and the agendas of development aid/loan programs. Deforestation can then lead to proximal drivers—such as soil runoff that increases pathogen transmission into water sources, and decreased forest resources—potentially leading to more intensive livestock husbandry to compensate for lost forest resources, which then may increase the risk of pathogen transmission via inadequate control of waste. An interdisciplinary systems approach can account for the varying temporal and spatial scales depicted in the figure and will foster collaboration in the collection and evaluation of data. outlines several measurable indicators relevant to health and sustainability within the water-related infectious disease cycle appropriate for the Ecuadorian example and identifies key contributing disciplines. The table highlights the need for interdisciplinary collaboration starting with conceptualization of the approach and continuing throughout.
Examples of indicators for water-related disease and control and the primary disciplines needed to contribute in the formulation and evaluation of each indicator.
This case study demonstrates the significant and intersecting roles played by multiple disciplines in understanding the causal linkages between road construction and disease. As examples, the political/economic disciplines shed light on why the road was built and its impact on the local economy of the region, whereas anthropology/ethnoecology studies describe the relationships between these larger-scale political/economic factors and the community’s social structures and how these affect behaviors, services, and infrastructures needed for disease prevention. In an analogous fashion, ecologic sciences and engineering describe impacts of the larger-scale processes on the environment in general and ultimately on water quality, and they also offer input into the assessment and design of actions to mitigate adverse environmental (and health) impacts. Public health has the role of both measuring the occurrence of disease through surveillance activities and evaluating the effectiveness of possible interventions. The challenge in such studies is to make these activities truly integrated and interdisciplinary. Barriers include differences in terminology and theoretical frameworks, which require working together to create protocols for collecting and analyzing data, and the need for sustained financial and institutional support, which can develop local capacity, understand the complex relationships, and ideally move beyond observational studies into intervention research. Ecuador could become a test case that both demonstrates the value of the proposed research approach and leads to improved health. Although many of the linkages between road construction and disease may be case-specific, such studies would show the utility of an interdisciplinary systems approach framework that incorporates the dynamics of infectious disease transmission within the social, ecologic, engineering, economic/political, and public health spheres discussed in this review.