Citizen science data on rodent indoor movement provide early warning of zoonotic risk

The triggers and timing of synanthropic behaviour of sylvatic reservoir rodents are largely unknown. Here, we used citizen science data on rodents observed indoors and reported in an app for surveillance of rodent-borne diseases. We related the app data to population dynamics of sylvatic small rodents, weather conditions, and human incidence of three notifiable diseases: tick-borne encephalitis (TBE), tularemia, and hemorrhagic fever with renal syndrome (HFRS). Citizen reports on voles and mice indoors were highest in winter, especially the winter following the vole peak. With a one-month time lag, the peak in vole reports was followed by a peak in HFRS incidence, while the time lag was 10 months for tularemia and TBE. Our results suggest that mild and rainy late autumns/winters drive wild rodents indoors, thereby increasing transmission risk of zoonotic pathogens. Citizen science data thus offer a valuable and promising tool for early warning and disease surveillance.