Broad-scale ecological niches of pathogens vectored by the ticks <i>Ixodes scapularis</i> and <i>Amblyomma americanum</i> in North America

Environmental dimensions, such as temperature, precipitation, humidity, and vegetation type, influence the activity, survival, and geographic distribution of tick species. Ticks are vectors of various pathogens that cause disease in humans, and <i>Ixodes scapularis</i> and <i>Amblyomma americanum</i> are among the tick species that transmit pathogens to humans across the central and eastern United States. Although their potential geographic distributions have been assessed broadly <i>via</i> ecological niche modeling, no comprehensive study has compared ecological niche signals between ticks and tick-borne pathogens. We took advantage of National Ecological Observatory Network (NEON) data for these two tick species and associated bacteria pathogens across North America. We used two novel statistical tests that consider sampling and absence data explicitly to perform these explorations: a univariate analysis based on randomization and resampling, and a permutational multivariate analysis of variance. Based on univariate analyses, in <i>Amblyomma americanum</i>, three pathogens <i>(Borrelia lonestari</i>, <i>Ehrlichia chaffeensis</i>, and <i>E. ewingii</i>) were tested; pathogens showed nonrandom distribution in at least one environmental dimension. Based on the PERMANOVA test, the null hypothesis that the environmental position and variation of pathogen-positive samples are equivalent to those of <i>A. americanum</i> could not be rejected for any of the pathogens, except for the pathogen <i>E. ewingii</i> in maximum and minimum vapor pressure and minimum temperature. For <i>Ixodes scapularis,</i> six pathogens (<i>A. phagocytophilum</i>, <i>Babesia microti</i>, <i>Borrelia burgdorferi</i> sensu lato, <i>B. mayonii</i>, <i>B. miyamotoi</i>, and <i>Ehrlichia muris</i>-like) were tested; only <i>B. miyamotoi</i> was not distinct from null expectations in all environmental dimensions, based on univariate tests. In the PERMANOVA analyses, the pathogens departed from null expectations for <i>B. microti</i> and <i>B. burgdorferi</i> sensu lato, with smaller niches in <i>B. microti</i>, and larger niches in <i>B. burgdorferi</i> sensu lato, than the vector. More generally, this study shows the value of large-scale data resources with consistent sampling methods, and known absences of key pathogens in particular samples, for answering public health questions, such as the relationship of presence and absence of pathogens in their hosts respect to environmental conditions.