Brinkworth, A. | Search bioRxiv

bioRxiv2026

Colonization of 3D-organotypic human skin by the Lyme Disease pathogen, Borrelia burgdorferi

Borrelia burgdorferi is a bacterial pathogen transmitted by ticks that is the causative agent of Lyme Disease. When studying interactions between B. burgdorferi and skin following a tick-bite, existing models consist primarily of murine skin which has different cellularity and thickness than human skin or ex vivo human biopsies that can be difficult to obtain and can have high variability. This presents a need for a reproducible human skin model. Herein, we adapt an existing human organotypic skin model that is simply composed of dermal fibroblasts and stratified epidermal keratinocytes and develop an infection assay mimicking skin reinfection to characterize B. burgdorferi colonization. Normal spirochete morphology and a stressed B. burgdorferi morphology known as a "round body" were observed. Peak B. burgdorferi invasion was observed at 24 hours (h) with peak round body formation at 48 h. By breaking the skin down into its individual components, we observed an increase in the number of round bodies in the presence of dermal fibroblasts. The presence of keratinocytes or extracellular matrix alone had no effect on round body formation, indicating a dermal fibroblast-mediated mechanism. We also demonstrate tissue-to-tissue dissemination and colonization, setting the groundwork for future studies with other tissues. Collectively, these results prove that this is a valid human skin model to study B. burgdorferi colonization during secondary dissemination.

microbiology↗

bioRxiv2026

When clades collide: Genomic admixture in blacklegged ticks (Ixodes scapularis) from the Great Plains

Ixodes scapularis ticks transmit a number of pathogens important to human health, including Borrelia burgdorferi, the causative agent of Lyme disease. While I. scapularis is found across the Eastern United States, Lyme disease transmission is largely limited to the Northeast and Upper Midwest and is nearly absent in the South. This indicates that differences in northern versus southern clades of I. scapularis are associated with differences in Lyme disease transmission risk. I. scapularis is undergoing range expansion, including into the Great Plains region of the United States. Determining where I. scapularis populations in the Great Plains originated can inform future risk of Lyme disease transmission in this region. In this study, we use a population genomics framework to characterize diversity, structure, and B. burgdorferi infection rates of I. scapularis populations in the Great Plains region. We generated whole genome sequence data and single nucleotide polymorphism (SNP) datasets from I. scapularis ticks collected in Iowa, Kansas, Nebraska, and South Dakota to compare to publicly available data from across the species range. Our analysis of 200 I. scapularis SNP datasets indicated geographically well-defined populations that correspond to historical northern and southern ancestral clades of I. scapularis. Ticks from South Dakota, Iowa, and northeastern Nebraska are genetically similar populations from the Upper Midwest, while ticks from Kansas are more genetically similar to ticks from the Southeast. Ticks collected in the central eastern region of Nebraska, however, represent an evenly admixed population of both northern and southern genomic backgrounds. Analysis of B. burgdorferi reads from genomic datasets shows [~]50% infection rate in ticks from Iowa and northeastern Nebraska, whereas ticks from Kansas show no evidence of B. burgdorferi infection. Of note, evenly admixed ticks from the central eastern region of Nebraska also show no evidence of B. burgdorferi infection. These results provide further evidence that tick genomics may influence traits associated with B. burgdorferi infection status, and thus the potential for Lyme disease transmission. As the range of I. scapularis continues to expand, bringing historically isolated populations into contact, there is a clear need to understand the consequence of genomic admixture for B. burgdorferi transmission potential to inform future risk of Lyme disease in the United States.

genomics↗