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Lyme disease is the most commonly reported vector-borne disease in the United States, and the number of cases reported each year continues to rise. The complex nature of the relationships between the pathogen (Borrelia burgdorferi sensu stricto), the tick vector (Ixodes scapularis Say), multiple vertebrate hosts, and numerous environmental factors creates challenges for understanding and predicting tick population and pathogen transmission dynamics. LYMESIM is a mechanistic model developed in the late 1990s to simulate the life-history of I. scapularis and transmission dynamics of B. burgdorferi s.s. Here we present LYMESIM 2.0, a modernized version of LYMESIM, that includes several modifications to enhance the biological realism of the model and to generate outcomes that are more readily measured under field conditions. The model is tested for three geographically distinct locations in New York, Minnesota, and Virginia. Model-simulated timing and densities of questing nymphs, infected nymphs, and abundances of nymphs feeding on hosts are consistent with field observations and reports for these locations. Sensitivity analysis highlighted the importance of temperature in host finding for the density of nymphs, the importance of transmission from small mammals to ticks on the density of infected nymphs, and temperature-related tick survival for both density of nymphs and infected nymphs. A key challenge for accurate modeling of these metrics is the need for regionally representative inputs for host populations and their fluctuations. LYMESIM 2.0 is a useful public health tool that downstream can be used to evaluate tick control interventions and can be adapted for other ticks and pathogens.

Introduction: The prevalence of Francisella tularensis in Minnesota ticks is unknown. Ticks collected at seven sites were tested to determine the infection prevalence of F. tularensis in D...

Tick-borne diseases, due to a diversity of bacterial pathogens, represent a significant and increasing public health threat throughout the Northern Hemisphere. A high-throughput 16S V1-V2 rRNA gene-based metagenomics assay was developed and evaluated using13,000 residual samples from patients suspected of having tick-borne illness and1,000 controls. Taxonomic predictions for tick-borne bacteria were exceptionally accurate, as independently validated by secondary testing. Overall, 881 specimens were positive for bacterial tick-borne agents. Twelve tick-borne bacterial species were detected, including two novel pathogens, representing a 100% increase in the number of tick-borne bacteria identified compared to what was possible by initial PCR testing. In three blood specimens, two tick-borne bacteria were simultaneously detected. Seven bacteria, not known to be tick transmitted, were also confirmed to be unique to samples from persons suspected of having tick-borne illness. These results indicate that 16S V1-V2 metagenomics can greatly simplify diagnosis and accelerate the discovery of bacterial tick-borne pathogens.

Ixodes scapularis is the vector of at least seven human pathogens in Minnesota, two of which are known to cause Lyme disease (Borrelia burgdorferi sensu stricto and Borrelia mayonii). In Minnesota, the statewide incidence of Lyme disease and other I. scapularis-borne diseases and the geographic extent over which cases have been reported have both increased substantially over the last two decades. These changes correspond with an expanding distribution of I. scapularis over a similar time frame. Because the risk of exposure to I. scapularis-borne pathogens is likely related to the number of ticks encountered, we developed an acarological risk model predicting the density of host-seeking I. scapularis nymphs (DON) in Minnesota. The model was informed by sampling 81 sites located in 42 counties in Minnesota. Two main foci were predicted by the model to support elevated densities of host-seeking I. scapularis nymphs, which included the seven-county Minneapolis-St. Paul metropolitan area and counties in northern Minnesota, including Lake of the Woods and Koochiching counties. There was substantial heterogeneity observed in predicted DON across the state at the county scale; however, counties classified as high risk for I. scapularis-borne diseases and counties with known established populations of I. scapularis had the highest proportion of the county predicted as suitable for host-seeking nymphs (≥ 0.13 nymphs/100 m2). The model provides insight into areas of potential I. scapularis population expansion and identifies focal areas of predicted suitable habitat within counties where the incidence of I. scapularis-borne diseases has been historically low.

BACKGROUND: Tick-transmitted Borrelia species fall into two heterogeneous bacterial complexes comprised of multiple species, the relapsing fever (RF) group and the Borrelia burgdorferi sensu lato group, which are the causative agents of Lyme borreliosis (LB), the most common tickborne disease in the northern hemisphere. Geographic expansion of human LB in the United States and discovery of emerging Borrelia pathogens underscores the importance of surveillance for disease causing Borrelia. METHODS: De-identified clinical specimens, submitted by providers throughout the United States, for patients suspected of LB, anaplasmosis, ehrlichiosis, or babesiosis, were screened using a Borrelia genus level TaqMan PCR. Borrelia species and sequence types (STs) were characterized by multi-locus sequence typing (MLST) utilizing next generation sequencing. RESULTS: Among the 7,292 tested specimens tested, five different Borrelia species were identified: two causing LB, B. burgdorferi (n=25) and B. mayonii (n=9), and three RF borreliae, B. hermsii (n=1), B. miyamotoi (n=8), and Candidatus B. johnsonii (n=1), a species previously detected only in the bat tick, Carios kelleyi. ST diversity was greatest for B. burgdorferi positive specimens, with new STs identified primarily among synovial fluids. CONCLUSION: These results demonstrate broad PCR screening followed by MLST is a powerful surveillance tool for uncovering the spectrum of Borrelia species causing human disease, improving understanding of their geographic distribution, and investigating the correlation between B. burgdorferi STs and joint involvement. Detection of Candidatus B. johnsonii in a patient with suspected tickborne disease suggests this species may be a previously undetected cause of illness in humans with exposure to bat ticks.

Ixodes scapularis Say, the black-legged tick, is the primary vector in the eastern United States of several pathogens causing human diseases including Lyme disease, anaplasmosis, and babesiosis. Over the past two decades, I. scapularis -borne diseases have increased in incidence as well as geographic distribution. Lyme disease exists in two major foci in the United States, one encompassing northeastern states and the other in the Upper Midwest. Minnesota represents a state with an appreciable increase in counties reporting I. scapularis -borne illnesses, suggesting geographic expansion of vector populations in recent years. Recent tick distribution records support this assumption. Here, we used those records to create a fine resolution, subcounty-level distribution model for I. scapularis using variable response curves in addition to tests of variable importance. The model identified 19% of Minnesota as potentially suitable for establishment of the tick and indicated with high accuracy (AUC = 0.863) that the distribution is driven by land cover type, summer precipitation, maximum summer temperatures, and annual temperature variation. We provide updated records of established populations near the northwestern species range limit and present a model that increases our understanding of the potential distribution of I. scapularis in Minnesota.

The distribution of I. scapularis, the tick vector of the bacteria that cause Lyme disease, has been expanding over the last two decades in the north-central United States in parallel with increasing incidence of human cases of Lyme disease in that region. However, assessments of residential risk for exposure to ticks are lacking from this region. Here, we measured the density of host-seeking I. scapularis nymphs in two suburban and two rural public recreational sites located in Washington County, Minnesota as well as in nearby residential properties. We sought to compare tick densities across land use types and to identify environmental factors that might impact nymphal density. We also assessed the prevalence of infection in the collected ticks with Lyme disease spirochetes (Borrelia burgdorferi sensu stricto, B. mayonii), and other I. scapularis-borne pathogens including B. miyamotoi, Babesia microti and Anaplasma phagocytophilum. Similar to studies from the eastern United States, on residential properties, I. scapularis nymphal densities were highest in the ecotonal areas between the forest edge and the lawn. Residences with the highest densities of nymphs were more likely to have a higher percentage of forest cover, log piles, and signs of deer on their property. In recreational areas, we found the highest nymphal densities both in the wooded areas next to trails as well as on mowed trails. Among the 303 host-seeking I. scapularis nymphs tested for pathogens, B. burgdorferi sensu stricto, A. phagocytophilum and B. miyamotoi were detected in 42 (13.8%), 14 (4.6%), and 2 (0.6%) nymphs, respectively.

Summary Background Lyme borreliosis is the most common tick-borne disease in the northern hemisphere. It is a multisystem disease caused by Borrelia burgdorferi sensu lato genospecies and characterised by tissue localisation and low spirochaetaemia. In this study we aimed to describe a novel Borrelia species causing Lyme borreliosis in the USA. Methods At the Mayo clinic, from 2003 to 2014, we tested routine clinical diagnostic specimens from patients in the USA with PCR targeting the oppA1 gene of B burgdorferi sensu lato. We identified positive specimens with an atypical PCR result (melting temperature outside of the expected range) by sequencing, microscopy, or culture. We collected Ixodes scapularis ticks from regions of suspected patient tick exposure and tested them by oppA1 PCR. Findings 100 545 specimens were submitted by physicians for routine PCR from Jan 1, 2003 to Sept 30, 2014. From these samples, six clinical specimens (five blood, one synovial fluid) yielded an atypical oppA1 PCR product, but no atypical results were detected before 2012. Five of the six patients with atypical PCR results had presented with fever, four had diffuse or focal rash, three had symptoms suggestive of neurological inclusion, and two were admitted to hospital. The sixth patient presented with knee pain and swelling. Motile spirochaetes were seen in blood samples from one patient and cultured from blood samples from two patients. Among the five blood specimens, the median oppA1 copy number was 180 times higher than that in 13 specimens that tested positive for B burgdorferi sensu stricto during the same time period. Multigene sequencing identified the spirochaete as a novel B burgdorferi sensu lato genospecies. This same genospecies was detected in ticks collected at a probable patient exposure site. Interpretation We describe a new pathogenic Borrelia burgdorferi sensu lato genospecies (candidatus Borrelia mayonii ) in the upper midwestern USA, which causes Lyme borreliosis with unusually high spirochaetaemia. Clinicians should be aware of this new B burgdorferi sensu lato genospecies, its distinct clinical features, and the usefulness of oppA1 PCR for diagnosis. Funding US Centers for Disease Control and Prevention Epidemiology and Laboratory Capacity for Infectious Diseases (ELC) Cooperative Agreement and Mayo Clinic Small Grant programme.

On June 27, 2016, the Minnesota Department of Health (MDH) Public Health Laboratory (PHL) was notified of a suspected Francisella tularensis isolate cultured at a hospital laboratory. The isolate was confirmed as F. tularensis type B at MDH PHL by reverse transcription-polymerase chain reaction, culture, and direct fluorescent antibody testing. Francisella tularensis subspecies tularensis (type A) and holarctica (type B) bacteria are the causative agents of tularemia.