Oak acorn crop and Google search volume predict Lyme disease risk in temperate Europe

Abstract

Lyme disease is a major zoonosis in the northern hemisphere. It is caused by the spirochete Borrelia burgdorferi, transmitted by ticks (genus Ixodes), and the abundance of infected tick nymphs determines the risk of the disease in humans. In eastern USA, fluctuations in oak (Quercus spp.) acorn production (including mast seeding) determine rodent abundance, which has been linked with Lyme borreliosis risk in humans. However, the predictive power of masting on Lyme disease risk in other systems has never been tested. We used a combination of field and Internet data to trace the ecological chain reaction that links acorn production by oaks and Lyme borreliosis risk in European forests. We found a positive relationship between oak acorn production (Q. robur and Q. petraea) in year T and the number of Lyme borreliosis incidences in year T+2. Acorn production was also positively correlated with Google search volume for the terms “tick” and “Lyme disease” two years later. Our results suggest that acorn production influences tick population, leading to fluctuations in the intensity of interactions between humans and ticks that can be seen in Google search dynamics. Thus, mast seeding together with the volume of specific Internet web searches appears to be a promising tool that could be used to alert public.