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Fell, Henry Gillies (2022) Testing the climatic controls on plague (Yersinia pestis) using palaeobiogeographical modelling and experimental microbiology. PhD thesis, University of Nottingham.

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Abstract

Yersinia pestis is the bacterial agent of plague, a disease which has caused three trans-continental pandemics through the Common Era. Y. pestis is currently present in reservoir populations in Asia, Africa, North and South America and has recently been identified as a re-emergent disease primarily due to increasing recorded cases across Africa. Plague is a zoonotic disease, the bacterial agent of which (Y. pestis) is transmitted and maintained primarily through rodent reservoir species and the ectoparasites which feed on them. The Y. pestis zoonotic disease system is therefore highly complex as the dynamics of the bacterium, vector and reservoir species can all impact transmission and dissemination.

In this thesis I focus on the niche of Y. pestis at two opposing spatial scales, macroecological and microbiological, and address three gaps in the literature across these scales. Firstly the degree to which reservoir (mammalian host) species locations dictate the distribution of Y. pestis compared to the environmental niche of Y. pestis per se is debated and the transferability of such niches between regions is rarely tested. I assess the niche differences between the Y. pestis at a continental scale across native and invaded ranges, finding that biotic factors, in this case reservoir species distribution, drive such differences.

Secondly Y. pestis has commonly been demonstrated to be a highly climatically dynamic disease and subsequently correlations are regularly observed between climatic variables and plague infection among human populations. The mediating factor between these elements of the plague system is often assumed to be a response of reservoir species to climate however the exact mechanisms driving this correlation are poorly resolved. I therefore assess the role that reservoir species play in mediating changes in human plague cases driven by climate perturbations, as has regularly been hypothesised. I find that the response of reservoir species to climatic conditions is highly variable and that even within a similar climatic regime the response of reservoir species to climatic variation should not be assumed to be homogeneous.

At the opposing end of the spatial scale much of the literature assumes that unlike it’s most recent ancestors Y. pestis is incapable of persisting independently of host and vector species within the environment. Selected recent works have challenged this assumption by suggesting that Y. pestis may be capable of surviving in soils. However, little work has experimentally tested the survival of Y. pestis in “real world” unsterilised soils or attempted to determine the impact of variables within the soil such as moisture and temperature on Y. pestis survival. Through experimental microbiology, I test the niche of Y. pestis within soil environments independent of reservoir and vector species. Survival of Y. pestis within soils is an often suggested mechanism to explain prolonged periods of quiescence but has yet to be fully integrated into models of the complex plague transmission and maintenance system. My work suggests that soil moisture is a key variable in enabling the persistence of Y. pestis in soil environments.

Integrating findings from such disparate scales into a cohesive model of a complex zoonotic disease system is a significant challenge which my work only begins to address. This work is however necessary to avoid the erroneous transfer of assumptions between scales and contexts, which is particularly relevant for plague given the global breadth of distribution in varying environments. My work will hopefully aid in contributing to a more holistic multiscale view of the Y. pestis disease system.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Matthew, Jones Steve, Atkinson Adam, Algar
Keywords:	Yersinia pestis, plague disease system, disease transmission, microbiology, paleobiogeography
Subjects:	Q Science > QH Natural history. Biology > QH540 Ecology Q Science > QR Microbiology
Faculties/Schools:	UK Campuses > Faculty of Social Sciences, Law and Education > School of Geography
Item ID:	69910
Depositing User:	Fell, Henry
Date Deposited:	25 Oct 2023 13:08
Last Modified:	25 Oct 2023 13:08
URI:	https://eprints.nottingham.ac.uk/id/eprint/69910

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