Weather and Climate

Individual weather events, short-term climate variability, and long-term climate change all influence human health. An important pathway for these effects is through environmentally sensitive infectious diseases caused by water-borne, vector- borne, and zoonotic pathogens. Geographic patterns of climate limit the distributions of vector and host species. Seasonal and interannual climate variations also influence the timing and abundance of vector and host populations. Climate-driven shifts in the hydrological cycle can cause flooding or drought, both of which have the potential to increase transmission of water-borne pathogens. Because of the complexity of transmission cycles, the effects of climate change on infectious disease risk depend on the biological characteristics of the species involved and the local physical and social environments in which transmission occurs.

We research the effects of climate variation on West Nile virus (WNV) in the United States and malaria in Ethiopia and India. During the 2003 WNV outbreak in the northern Great Plains, the highest incidence occurred in locations with warmer temperatures and intermediate levels of precipitation (Wimberly et al. 2008). Subsequent outbreaks occurred in years with higher than usual temperature during the transmission season and the preceding winter (Wimberly et al. 2014). In Ethiopia, warmer temperatures were associated with malaria outbreaks in wetter districts, whereas rainfall and moisture indices had stronger influences in drier districts (Midekisa et al. 2015). These associations provide the basis for developing early-warning systems that predict future disease risk based on lagged responses to climate variations (Midekisa et al. 2012, Davis et al. 2019).


Land Cover and Land Use

Land cover encompasses the biophysical characteristics of the Earth’s surface, whereas land use describes the human activities occurring on the landscape. Vegetation, hydrology, and built-up areas affect habitat suitability for disease-transmitting vectors and reservoir hosts. Land use associated with urbanization, agriculture, and resource extraction fragment natural habitats and influence human exposure to vectors, hosts, and pathogens. Land cover also modifies microclimate and can create refugia that allow vector and host species to persist in climate that would otherwise be unsuitable. The effects of land cover and land use on vector-borne disease risk depend on the scale of the analysis and the local geographic context. In the northern Great Plains of the United States where Culex tarsalis is the primary vector of WNV, incidence is highest in rural valleys dominated by grasslands and lowest in cities and in mountainous regions covered by forests (Chuang et al., 2012; Hess et al. 2018). In the Amhara region of Ethiopia, malaria incidence from 2007-2009 was highest in districts with extensive wetland cover (Midekisa et al. 2014). A more localized study of malaria patterns within four districts found that incidence was highest in areas with low vegetation cover and were also associated with the density and spatial aggregation of human settlements (McMahon et al. 2021).


Social Environments

The social environment encompasses culture, individual relationships, economic opportunities, and institutions as well as aspects of the built environment. These factors affect access to healthy foods, physical activity, and health care, which are important risk factors for multiple chronic diseases. Social environments also affect exposures to pollutants, toxins, and disease-transmitting vectors and hosts. We mapped obesity and associated risk factors at a county level for the conterminous United States, and we analyzed their relationships with supermarket accessibility (Michimi and Wimberly 2010b). The prevalence of obesity increased with distance to supermarkets in metropolitan counties, but no relationship was found in non-metropolitan counties (Michimi and Wimberly 2010a). An analysis of obesity rates in major U.S. cities similarly found positive associations with the proportions of supermarket and full-service restaurants and negatively associated with fast-food and convenience stores (Michimi and Wimberly 2015). In non-metropolitan counties, obesity was lowest in counties with abundant recreational opportunities, including parks, trails, and other outdoor amenities (Michimi and Wimberly 2012). Rural isolation and accessibility of health care can have substantial impacts on health outcomes following a cancer diagnosis. In South Dakota, one of the most sparsely populated U.S. states, isolated rural communities, which also had high levels of economic deprivation, had increased risk of late-stage colorectal cancer diagnosis (Lin and Wimberly 2017). Patients with better geographic access to radiation therapy facilities were found to have a higher probability of receiving radiation therapy versus mastectomy as treatment for breast cancer (Lin and Wimberly 2018).