David Simmons: Land use gradients drive spatial variation in Lassa fever host communities in the Eastern Province of Sierra Leone

Land use change, particularly the conversion of natural habitats into agricultural or urban landscapes, is a key driver of biodiversity loss, reducing mammalian species diversity across several dimensions (Newbold et al., 2015). These include taxonomic diversity (the number and relative abundance of taxa), functional diversity (the range of roles organisms play within an ecosystem) and interaction diversity (the biotic interactions among species) (Glidden et al., 2021; Naeem et al., 2012). These declines in biodiversity, particularly in rodent-associated disease systems, may exacerbate zoonotic disease risks by promoting the proliferation of generalist, synanthropic rodents that thrive in human-modified landscapes, where they host zoonotic pathogens (Ecke et al., 2022; Gibb et al., 2020; Young et al., 2014). This shift may therefore not only increase the prevalence of zoonotic pathogens but also human exposure in complex socio-ecological systems (Gibb et al., 2025).

The role of host community diversity in mediating zoonotic outbreaks is nuanced, with changes in species composition and pathogen prevalence often interacting with anthropogenic stressors to create context-specific outcomes (Carlson et al., 2025; Gibb et al., 2020; Keesing & Ostfeld, 2021). A deeper mechanistic understanding of these processes, including community structure, biotic interactions and responses to anthropogenic land use change, is critical for leveraging biodiversity knowledge to predict and mitigate zoonotic risks (Carlson et al., 2025; Glidden et al., 2021; Salkeld et al., 2013). These approaches have only been taken for a few rodent-associated zoonoses (Keesing & Ostfeld, 2024).

Rodents are an important mammalian host taxa for zoonotic diseases (Han et al., 2015; Mendoza et al., 2019). Rodent-associated zoonoses, such as Lyme disease caused by Borrelia burgdorferi sensu lato, have been shown to involve a complex interplay of community structure, biotic interactions, and the effect of land use change (Ostfeld & Holt, 2004). For instance, land use change can increase reservoir abundance and subsequently zoonotic risk, though responses vary across systems and settings, highlighting the idosyncratic or system specific nature of these dynamics (Mendoza et al., 2019; Pei et al., 2024; Young et al., 2017).

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