Climate Change and Nipah virus: exploring the links between climate variability, extremes, and zoonotic spillover in Bangladesh

Zoonotic infectious diseases, transmitted from wild or domestic animals into humans, represent a major threat for public health as they can cause serious disease outbreaks and potentially escalate into pandemics, as recently observed for SARS-2-Covid-19. Climate change and anthropogenic ecosystem alterations are amplifying this risk by reshaping interactions between wildlife, pathogens, and human populations. Consequently, “jump-zones”-regions where zoonotic spillovers are increasingly likely-are fast expanding, particularly at tropics. Among bat-borne zoonoses, Nipah virus (NiV) is recognized by the World Health Organization as one of the top 10 priority diseases, causing near-annual outbreaks in Bangladesh, a region highly vulnerable to climate change impacts. Despite the critical role bats play in pathogen transmission, their responses to climatic factors remains largely underexplored, highlighting the urgent need for focused research, also in view of the current climate change. This thesis investigates the relationship between relevant climatic factors, including extreme weather events, and Nipah virus spillover occurrences in Bangladesh, where fruit bats (Pteropus species) serve as natural reservoirs of the virus. Through detailed spatio-temporal analysis, coupled with a regression analysis using Generalized Linear Models (GLMs), this study aims to identify key climate variables influencing the frequency and spatial distribution of spillover events occurred over a 18-year period (2001-2018). Furthermore, addressing gaps identified in the literature, this study extends the temporal focus beyond the typical winter months to examine year-round climate dynamics, using ERA5 reanalysis data, which provides higher spatial resolution and more reliable climate information for tropical regions than traditional sources. Key findings reveal that specific climate conditions—colder winters, warmer and drier monsoons, and reduced post-monsoon rainfall—are strongly associated with a surge in NiV spillover events. These climatic stressors likely disrupt bat foraging and increase thermoregulatory stress, which are known to drive recrudescence and shedding of virus. Notably, the observed correlation between monsoon conditions and the frequency of spillover events is a novel finding for the Nipah virus in Bangladesh, although similar pattern have been observed with Hendra virus, another paramyxovirus, in Australia. Additionally, the spatial analysis identified two distinct geographic clusters within the Nipah Belt, each defined by specific climatic and environmental stressors. This underscores the spatial heterogeneity of spillover risk drivers and emphasizes the importance of targeted, region-specific interventions to mitigate spillover risks. Given the accelerated pace of climate change impacts, and its complex interaction with bat behaviour and viral dynamics, a deeper understanding of the climatic triggers associated with spillover events is crucial. Such knowledge could enhance predictive models, supporting the design of targeted interventions to prevent or mitigate NiV outbreaks, particularly in high-risk regions.