Interacting effects of land use and climate on rodent-borne pathogens in central Kenya

Abstract

Understanding the effects of anthropogenic disturbance on zoonotic disease risk is both a critical conservation objective and a public health priority. Here, we evaluate the effects of multiple forms of anthropogenic disturbance across a precipitation gradient on the abundance of pathogen-infected small mammal hosts in a multi-host, multi-pathogen system in central Kenya. Our results suggest that conversion to cropland and wildlife loss alone drive systematic increases in rodent-borne pathogen prevalence, but that pastoral conversion has no such systematic effects. The effects are most likely explained both by changes in total small mammal abundance, and by changes in relative abundance of a few high-competence species, although changes in vector assemblages may also be involved. Several pathogens responded to interactions between disturbance type and climatic conditions, suggesting the potential for synergistic effects of anthropogenic disturbance and climate change on the distribution of disease risk. Overall, these results indicate that conservation can be an effective tool for reducing abundance of rodent-borne pathogens in some contexts (e.g. wildlife loss alone); however, given the strong variation in effects across disturbance types, pathogen taxa and environmental conditions, the use of conservation as public health interventions will need to be carefully tailored to specific pathogens and human contexts.This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications’.

Conservation, biodiversity and infectious disease: scientific evidence and policy implications

“…Conservation can benefit public health [28,29], but this is neither a general nor simple outcome. Instead, disturbance and conservation can increase or decrease disease risk, depending on the pathogen involved, the disturbance type and the environmental context [25,27,32]. Despite this lack of a generalizable relationship between biodiversity, conservation and infectious diseases, many infectious diseases are better understood and managed in an ecological context.…”

“…Instead, disease risk reflects changes in small mammal abundance and community composition, with the dominant mechanisms depending on the disturbance considered. Young et al [27] conclude that, although conservation might reduce some disease, careful pathogen and disturbance-specific studies are needed before recommending specific interventions.…”

Climatic variation modulates the indirect effects of large herbivores on small‐mammal habitat use

“…Finally, the responses of small mammals to LMH exclusion observed in our study have potential to increase the frequency of interactions, both direct and indirect, between small mammals and humans. Small mammals serve as zoonotic disease reservoirs in our system and elsewhere (Howe, Brown & Zorn-Arnold 2002;Ostfeld et al 2006;Young et al 2017) and can be major agricultural pests (Leirs et al 1996;Stenseth et al 2003). Negative effects of small mammals on human livelihoods may, therefore, be a non-trivial unanticipated consequence of LMH declines in a changing climate (du Toit & Cumming 1999).…”

“…Understanding the mechanisms by which herbivoreinitiated interaction pathways induce changes in small-mammal behaviour and activity patterns may help us understand how small mammals influence ecosystem processes (Keesing & Crawford 2001;Johnston & Anthony 2008). Release of small-mammal abundance from competition with LMH has been shown to increase ectoparasite abundance and zoonotic disease risk (Ostfeld et al 2006;Young et al 2017), as well as seed-predation pressure ). Yet, changes in the spatial distribution, activity patterns and other behaviours of small mammals-irrespective of any increase in abundance-can also affect seed dispersal (Hirsch et al 2012;Steele et al 2014), disease transmission (Page, Swihart & Kazacos 2001) and agricultural damage (Schauber et al 2009).…”

Rodent-borne health risks in farming systems

“…Each pathogen has its own, specific lifecycle and requirements to its environment (Beard, Garafalo, & Gage, 2015;Hansen et al, 2016;Rood, Goris, Pijnacker, Bakker, & Hartskeerl, 2017;Young et al, 2017). Although the disease transmission involves more than one cause, global climate change could be a significant driver.…”