Geographic trends in acarological risk reporting for <i>Ixodes scapularis</i> (Acari: Ixodidae)-borne infections across the eastern United States based on data submissions to the ArboNET Tick Module, 2004 to 2023

The United States Centers for Disease Control and Prevention introduced the National Tick Surveillance Program in 2018 to better define areas of acarologic risk in response to the increasing burden of blacklegged tick (Ixodes scapularis, Acari: Ixodidae)-associated infections. The program coordinates surveillance efforts conducted by state and local public health programs and collates acarological data in the ArboNET Tick Module national database. Among the metrics collected, the density of infected host-seeking nymphs (DIN) is believed to be most closely correlated with the reported occurrence of tick-borne diseases. Here, we assess the completeness and geographic representativeness of pathogen-specific DIN data collected from 2004 to 2023 and reported to the ArboNET Tick Module. We summarize county, state, and regional variation in the density of host-seeking I. scapularis nymphs infected with 6 human pathogens: Borrelia burgdorfieri sensu stricto (Spirochaetales: Spirochaetaceae), Borrelia mayonii (Spirochaetales: Spirochaetaceae), Borrelia miyamotoi (Spirochaetales: Spirochaetaceae), Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), Ehrlichia muris eauclairensis (Rickettsiales: Ehrlichiaceae), and Babesia microti (Piroplasmida:Babesiidae). Although DIN data submissions have increased from the first to the second decade of surveillance in some regions (Northeast, Ohio Valley, Northern Rockies and Plains), they have decreased in other regions (South, Southeast). For a majority of counties across all regions, county DIN estimates were largely based on only a single annual DIN estimate per pathogen over the nearly 20 yr of surveillance. Despite the sparseness of DIN records in ArboNET, we show that acarological risk for Lyme disease has expanded geographically over the past 2 decades, and we present acarological risk maps for other I. scapularis-borne infections across the eastern United States.