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Doctoral thesis, 2017

Puumala virus dynamics in bank voles along habitat and community gradients

Khalil, Hussein


The majority of recent infectious disease outbreaks are zoonotic, i.e. caused by pathogens shared between humans and other vertebrates, and many of those originate in wildlife. The life cycle of zoonotic diseases is complex, and involves at least one non-human host. To adequately assess human risk, we need to understand relevant ecological interactions driving host and pathogen populations. Puumala hantavirus (PUUV) is a directly transmitted pathogen, carried by the bank vole (Myodes glareolus), and causes a mild form of haemorrhagic fever in humans. Using long-term data from a 100 × 100 km study area, my project aimed to improve spatial and temporal predictions of PUUV risk in northern Sweden. I was interested in how community interactions influence bank vole abundance and infection rates, in an ecosystem where several species recently declined. We found that either overall density or density of infected voles can be used to predict incidence in humans, and the predictor of choice depends on the seasonal relationship between bank vole density and PUUV prevalence. Also, bank vole density and distribution in the landscape at the beginning of a vole population cycle can predict peak human risk during that cycle, approximately 18 months later. To identify plots with infected bank voles, we developed and successfully validated a model based on microhabitat variables. Amongst others, important variables were related to cover, e.g. large holes, and resource availability, e.g. bilberry shrubs. Community interactions contributed to both host and pathogen dynamics, and we found evidence for the dilution effect, by which non-host species may reduce PUUV prevalence or host density. The decline in Tengmalm’s owl (Aegolius funereus), an important predator of voles, coincided with a long-term increase in the density of infected bank voles, and owls were more likely to prey on infected bank voles in less isolated forest patches. PUUV prevalence declined with common shrew (Sorex araneus) density, while bank vole density decreased as field vole (Microtus agrestis) density increased in clear-cuts. The present work enables public health professionals to forecast PUUV outbreaks and predict the spatial distribution of infected voles. Further, authorities and other stakeholders ought to conserve and promote functional diversity in the ecosystem, given the potential of competitors and predators to reduce human risk.


bank vole; dilution effect; disease ecology; nephropathia epidemica; puumala virus; zoonosis

Published in

Acta Universitatis Agriculturae Sueciae
2017, number: 2017:32
ISBN: 978-91-576-8837-8, eISBN: 978-91-576-8838-5
Publisher: Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies

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