Newer Surveillance Data Extends our Understanding of the Niche ofRickettsia montanensis(Rickettsiales: Rickettsiaceae) Infection of the American Dog Tick (Acari: Ixodidae) in the United States

Abstract

AbstractBackgroundUnderstanding the geographic distribution ofRickettsia montanensisinfections inDermacentor variabilisis important for tick-borne disease management in the United States, as both a tick-borne agent of interest and a potential confounder in surveillance of other rickettsial diseases. Two previous studies modeled niche suitability forD. variabiliswith and withoutR. montanensis, from 2002-2012, indicating that theD. variabilisniche overestimates the infected niche. This study updates these, adding data since 2012.MethodsNewer surveillance and testing data were used to update Species Distribution Models (SDMs) ofD. variabilis, andR. montanensisinfectedD. variabilis, in the United States. Using random forest (RF) models, found to perform best in previous work, we updated the SDMs and compared them with prior results. Warren’s I niche overlap metric was used to compare between predicted suitability for all ticks and ‘pathogen positive niche’ models across datasets.ResultsWarren’s I indicated <2% change in predicted niche, and there was no change in order of importance of environmental predictors, forD. variabilisorR. montanensispositive niche. The updatedD. variabilisniche model overpredicted suitability compared to the updatedR. montanensispositive niche in key peripheral parts of the range, but slightly underpredicted through the northern and midwestern parts of the range. This reinforces previous findings of a more constrained pathogen-positive niche than predicted byD. variabilisrecords alone.ConclusionsThe consistency of predicted niche suitability forD. variabilisin the United States, with the addition of nearly a decade of new data, corroborates this is a species with generalist habitat requirements. Yet a slight shift in updated niche distribution, even of low suitability, included more southern areas, pointing to a need for continued and extended monitoring and surveillance. This further underscores the importance of revisiting vector and vector-borne disease distribution maps.