Environmental Drivers of Infectious Diseases in a Changing Climate

Similar to other ecological systems, the dynamics of infectious diseases are driven by both intrinsic factors, such as system nonlinearity, and extrinsic factors, including vaccination, non-pharmaceutical interventions, and environmental drivers. Climate factors are key drivers of the seasonality of many infectious disease transmissions and influence interannual variability and long-term dynamics across different climate change scenarios. Pathogens sensitive to climate include those causing enteric diseases, vector-borne infections, and respiratory illnesses, among others. Nevertheless, understanding these impacts at a mechanistic level remains an active area of research. Here, I present recent findings on two climate-sensitive pathogens—malaria and influenza. We analyzed long-term malaria transmission by fitting nonlinear mechanistic models to partially observed data using an iterated maximum-likelihood filtering approach. We found that a temporary slowdown in global warming and changes in climate variability are likely driving the decline in malaria incidence in the East African highlands. We also examined how current and projected climates influence influenza spatiotemporal dynamics by integrating a multivariate regression model with a mechanistic transmission model. We identified a bimodal association between specific humidity and influenza transmission, with cases peaking at both low and high levels in Bangladesh. Climate projections indicate that highly populated areas are more likely to experience sharp increases during the monsoon. These findings highlight the importance of climate drivers as external factors in nonlinear epidemiological systems, with implications for both pathogen ecology and public health under current and future climate scenarios.