Remotely sensed vegetation moisture and Lyme borreliosis

Ixodes ricinus is in Europe the main vector of the bacterium Borrelia burgdorferi (Bb), the pathogenic agent of Lyme borreliosis (LB). Several studies report on the importance of humidity as one of the various environmental variables determining tick abundance, questing behavior and preference for humid woodlands with abundant undergrowth and a thick litter layer. On the basis of several studies addressing the connection between humidity and ticks, this study dwells into the question of whether the observed LB epidemiological pattern could be related to energy reflected by vegetative systems and measured by spaceborne sensors in segments of the electromagnetic spectrum that are sensitive to humidity. Time series of vegetation indices that are sensitive to vegetation greenness and moisture were tested as explanatory variables of LB incidence and we found that these indices carry information that relate to disease incidence records. This has revealed the potential of spaceborne data sources to be incorporated in disease monitoring schemes. This connection was revealed after performing a wavelet-based multiresolution analysis that allowed the examination of the remote sensing signal at different temporal scales. The study sites were located in Belgium, one of the Western European countries reporting remarkable increases in LB incidence in recent years.