Infectious disease burdens vary from country to country and year to year due to ecological and economic drivers. Recently, the World Health Organization (WHO) estimated country-level morbidity and mortality associated with a variety of factors, including infectious diseases, for the years 1990 and 2010. Unlike other databases that report disease prevalence or count outbreaks per country, the WHO dataset reports health impacts in per-person disability-adjusted life years (DALYs), allowing comparison across diseases with both lethal and sub-lethal health effects.
We investigated the spatial and temporal relationships between DALYs lost to infectious disease and potential demographic, economic, environmental, and biotic drivers, for the 60 intermediate-sized countries where data were available and comparable. Most drivers had unique associations with each disease. For example, temperature was positively associated with some diseases and negatively associated with others, perhaps due to differences in disease agent thermal optima, transmission modes, and host species identities. Biodiverse countries tended to have high disease burdens, consistent with the expectation that high diversity of potential hosts should support high disease transmission. Contrary to the dilution effect hypothesis, increases in biodiversity over time were not correlated with improvements in human health, and increases in forestation over time were associated with increased disease burden. Urbanization and wealth were associated with lower burdens for many diseases, a pattern that could arise from increased access to sanitation and health care in cities and increased investment in health care. The importance of urbanization and wealth helps to explain why most infectious diseases have become less burdensome over the past three decades, and points to possible levers for further progress in improving global public health.