Publications

Increasing Risk for Tick-Borne Disease: What Should Clinicians Know? Many of the diverse tick-borne diseases (TBD) in the US appear to be increasing in incidence, leading to concern that factors such as climate change may create challenging scenarios. The 18 TBD and 1 syndrome that cause illnesses in US residents present varying public health burdens. For US clinicians, the most common TBD of concern is Lyme disease (estimated at about 476 000 cases each year1), with babesiosis, human granulocytic anaplasmosis (HGA), Rocky Mountain spotted fever, monocytic ehrlichiosis (HME), and alpha gal allergy (ie, red meat allergy) annually accounting for hundreds to thousands of cases. The remaining TBD are either rare (≤50 cases/y) or diagnosed sporadically every few years, although some of these carry severe morbidity or mortality. TBD cases have increased within the last decade, but the cause for this trend is multifactorial. Changes in case reporting and case definitions have contributed to the increase, as have improved diagnostic capacity, demographic shifts, urbanization, and an expansion in the range and local abundance of tick vectors.

Powassan virus persistence after acute infection Survivors of Powassan encephalitis often have persistent neurological disease. A new mouse model replicates some elements of the human disease and demonstrates the presence of viral RNA in the brain as well as myelitis more than 2 mo after the acute infection. The related tick-borne encephalitis and West Nile Neuroinvasive Disease (WNND) also have common neurological sequelae, and models for these better-studied diseases provide evidence for prolonged virus, RNA, and inflammation in some cases, in addition to damage from the acute encephalitic disease. A better understanding of the biological basis for persistent signs and symptoms after Powassan encephalitis, currently a rare disease, could benefit from further studies of the more prevalent flaviviral encephalitides.

Comparative reservoir competence of Peromyscus leucopus, C57BL/6J, and C3H/HeN for Borrelia burgdorferi B31 Although laboratory strains of Mus musculus mice have successfully been leveraged to model acute human Lyme disease, the ability of these rodents to model B. burgdorferi-P. leucopus interactions remains understudied. Here, we compared infection of P. leucopus with B. burgdorferi B31 with infection of the traditional B. burgdorferi murine models-C57BL/6J and C3H/HeN Mus musculus, which develop signs of inflammation akin to human disease. We find that B. burgdorferi was able to reach much higher burdens (10- to 30-times higher) in multiple M. musculus skin sites and that the overall dynamics of infection differed between the two rodent species. We also found that P. leucopus remained transmissive to larval Ixodes scapularis for a far shorter period than either M. musculus strain. In line with these observations, we found that P. leucopus does launch a modest but sustained inflammatory response against B. burgdorferi in the skin.

Borrelia burgdorferi initiates early transcriptional re-programming in macrophages that supports long-term suppression of inflammation Borrelia burgdorferi (Bb), the causative agent of Lyme disease, establishes a long-term infection and leads to disease manifestations that are the result of host immune responses to the pathogen. Inflammatory manifestations resolve spontaneously despite continued bacterial presence, suggesting inflammatory cells become less responsive over time. This is mimicked by in vitro repeated stimulations, resulting in tolerance, a phenotypic subset of innate immune memory. We performed comparative transcriptional analysis of macrophages in acute and memory states and identified sets of Tolerized, Hyper-Induced, Secondary-Induced and Hyper-Suppressed genes resulting from memory induction, revealing previously unexplored networks of genes affected by cellular re-programming.

Single-cell RNA sequencing of murine ankle joints over time reveals distinct transcriptional changes following Borrelia burgdorferi infection Lyme disease is caused by the bacterial pathogen Borrelia burgdorferi, which can be readily modeled in laboratory mice. In order to understand the cellular and transcriptional changes that occur during B. burgdorferi infection, we conducted single-cell RNA sequencing (scRNA-seq) of ankle joints of infected C57BL/6 mice over time. We found that macrophages/monocytes, T cells, synoviocytes and fibroblasts all showed significant differences in gene expression of both inflammatory and non-inflammatory genes that peaked early and returned to baseline before the typical resolution of arthritis. Predictions of cellular interactions showed that macrophages appear to communicate extensively between different clusters of macrophages as well as with fibroblasts and synoviocytes. Our data give unique insights into the interactions between B. burgdorferi and the murine immune system over time and allow for a better understanding of mechanisms by which the dysregulation of the immune response may lead to prolonged symptoms in some patients.

Lizards and the enzootic cycle of Borrelia burgdorferi sensu lato Emerging and re-emerging pathogens often stem from zoonotic origins, cycling between humans and animals, and are frequently vectored and maintained by hematophagous arthropod vectors. The efficiency by which these disease agents are successfully transmitted between vertebrate hosts is influenced by many factors, including the host on which a vector feeds. The Lyme disease bacterium Borrelia burgdorferi sensu lato has adapted to survive in complex host environments, vectored by Ixodes ticks, and maintained in multiple vertebrate hosts. The versatility of Lyme borreliae in disparate host milieus is a compelling platform to investigate mechanisms dictating pathogen transmission through complex networks of vertebrates and ticks. We summarize the current evidence, spanning from field surveillance to laboratory infection studies, supporting the lizard contributions to Lyme borreliae circulation.

Structural evolution of an immune evasion determinant shapes pathogen host tropism Modern infectious disease outbreaks often involve changes in host tropism, the preferential adaptation of pathogens to specific hosts. The Lyme disease-causing bacterium Borrelia burgdorferi (Bb) is an ideal model to investigate the molecular mechanisms of host tropism, because different variants of these tick-transmitted bacteria are distinctly maintained in rodents or bird reservoir hosts. To survive in hosts and escape complement-mediated immune clearance, Bb produces the outer surface protein CspZ that binds the complement inhibitor factor H (FH) to facilitate bacterial dissemination in vertebrates. Despite high sequence conservation, CspZ variants differ in human FH-binding ability. Together with the FH polymorphisms between vertebrate hosts, these findings suggest that minor sequence variation in this bacterial outer surface protein may confer dramatic differences in host-specific, FH-binding-mediated infectivity.

Whole genome sequencing of human Borrelia burgdorferi isolates reveals linked blocks of accessory genome elements located on plasmids and associated with human dissemination Lyme disease is the most common vector-borne disease in North America and Europe. The clinical manifestations of Lyme disease vary based on the genospecies of the infecting Borrelia burgdorferi spirochete, but the microbial genetic elements underlying these associations are not known. Here, we report the whole genome sequence (WGS) and analysis of 299 B. burgdorferi (Bb) isolates derived from patients in the Eastern and Midwestern US and Central Europe. We develop a WGS-based classification of Bb isolates, confirm and extend the findings of previous single- and multi-locus typing systems, define the plasmid profiles of human-infectious Bb isolates, annotate the core and strain-variable surface lipoproteome, and identify loci associated with disseminated infection.

An AP-3-dependent pathway directs phagosome fusion with Rab8 and Rab11 vesicles involved in TLR2 signaling Intracellular compartmentalization of ligands, receptors and signaling molecules has been recognized as an important regulator of inflammation. The toll-like receptor (TLR) 2 pathway utilizes the trafficking molecule adaptor protein 3 (AP-3) to activate interleukin (IL)-6 signaling from within phagosomal compartments. To better understand the vesicular pathways that may contribute to intracellular signaling and cooperate with AP-3, we performed a vesicular siRNA screen. We identified Rab8 and Rab11 GTPases as important in IL-6 induction upon stimulation with the TLR2 ligand Pam3 CSK4 or the pathogen, Borrelia burgdorferi (Bb), the causative agent of Lyme disease. These Rabs were recruited to late and lysosomal stage phagosomes and co-transported with TLR2 signaling adaptors and effectors, such as MyD88, TRAM and TAK1, in an AP-3-dependent manner. Our data support a model where AP-3 mediates the recruitment of recycling and secretory vesicles and the assembly of signaling complexes at the phagosome.

Outer surface lipoproteins from the Lyme disease spirochete exploit the molecular switch mechanism of the complement protease C1s Proteolytic cascades comprise several important physiological systems, including a primary arm of innate immunity called the complement cascade. To safeguard against complement-mediated attack, the etiologic agent of Lyme disease, Borreliella burgdorferi, produces numerous outer surface-localized lipoproteins that contribute to successful complement evasion. Recently, we discovered a pair of B. burgdorferi surface lipoproteins of the OspEF-related protein family-termed ElpB and ElpQ-that inhibit antibody-mediated complement activation. In this study, we investigate the molecular mechanism of ElpB and ElpQ complement inhibition using an array of biochemical and biophysical approaches.  We propose a model whereby ElpB and ElpQ exploit activation-induced conformational changes that are normally important for C1s-mediated C4 cleavage. Our study expands the known complement evasion mechanisms of microbial pathogens and reveals a novel molecular mechanism for selective C1s inhibition by Lyme disease spirochetes.