Identifying factors that drive infection dynamics in reservoir host populations is essential in understanding human risk from wildlife-originated zoonoses. We studied zoonotic Puumala orthohantavirus (PUUV) in the host, the bank vole (Myodes glareolus), populations in relation to the host population, rodent and predator community and environment-related factors and whether these processes are translated into human infection incidence. We used 5-year rodent trapping and bank vole PUUV serology data collected from 30 sites located in 24 municipalities in Finland. We found that PUUV seroprevalence was negatively associated with the abundance of red foxes, but this process did not translate into human disease incidence, which showed no association with PUUV seroprevalence. The abundance of weasels, the proportion of juvenile bank voles in the host populations and rodent species diversity were negatively associated with the abundance index of PUUV-positive bank voles, which, in turn, showed a positive association with human disease incidence. Our results suggest certain predators, high proportion of young bank vole individuals and a diverse rodent community, may reduce PUUV risk for humans through their negative impacts on the abundance of infected bank voles.

Bank voles and other rodents (all together eight rodent species) were trapped at 30 study sites located in 24 municipalities across the Southern half of Finland. The study sites were located along a route across the south part of Finland with circa 30 km intervals. At each site, in total 150 snap traps were set with circa 10 meters intervals along 2–4 transects, which were located in forests and on the border between forests and agricultural fields. The trappings were carried out during September – October from 2001 to 2005. In 2001, 2002, 2004 and 2005, trappings were carried out for two continuous days (traps were set on day 1, checked and reset on day 2 and checked and removed on day 3). In 2003, the trappings were only performed at every second trapping site, lasting for only one day. All captured small mammals were frozen in dry ice in the field and later stored at -20 °C until further processing. The captured bank voles were thawed and dissected. Organ and tissue samples were taken, and the heart was placed in a microtube with 200 µl of PBS (phosphate-buffered saline). The elution was used in immunofluorescence assay (IFA) to detect antibodies against PUUV.

Data on human NE cases between 2001 and 2005 were provided by the Finnish National Institute for Health and Welfare from the Finnish National Infectious Diseases Register (https://thl.fi/en/web/infectious-diseases-and-vaccinations/surveillance-and-registers/finnish-national-infectious-diseases-register) for each of the 24 municipalities where the 30 rodent trapping sites were located.

Human population size of each municipality in 2005 was extracted from Statistics Finland (http://www.stat.fi/org/avoindata/paikkatietoaineistot_en.html).

Predator data for 5 km buffer zones around each of the 30 trapping sites between 2001 and 2005 were obtained from snow track index data collected within the Finnish Wildlife Triangle Scheme, by Natural Resources Institute Finland (LUKE) (https://www.riistakolmiot.fi).

Land cover data, including percentage of forests and semi-natural areas, artificial surfaces, agricultural areas, wetlands, and water bodies within each 5 km buffer zone around trapping sites from 2000 to 2005, were obtained from CORINE Land Cover 2006 project (https://www.syke.fi/fi).

Climate data, including seasonal average temperatures and precipitation within each 5 km buffer zone from 2001 to 2005 based on monthly air temperature and precipitation from the Finnish Meteorological Institute (https://en.ilmatieteenlaitos.fi/climate–statistics). Seasons were defined following as "winter" (January, February, March), "spring" (April and May), "summer" (June, July and August) and "autumn" (October, November and December).

Human population size, predator data, land cover data and climate data were extracted using ArcGIS.